Bitcoin Wiki - User contributions [en]

How to set up a secure offline savings wallet

2012-11-30T21:40:53Z

Jepo: /* Why set up an offline savings wallet? */ link to "Wallet"

== Why set up an offline savings wallet? ==

Modern operating systems are getting more and more complex. The flip side of all this complexity is that they generally have a large [http://en.wikipedia.org/wiki/Attack_surface attack surface] and constantly leak information without the user’s knowledge or consent. No matter how many precautions you take, your [[wallet]]s will never be 100% safe on a computer that is connected to the internet.

Because bitcoins are stored directly on your computer and because they are real money, the motivation for sophisticated and targeted attacks against your system is higher than in the pre-bitcoin era, when only large organizations normally had to worry about such attacks.

This guide will instruct you on how to create an offline wallet, a wallet that never even touches the internet in its plaintext form. Another term for this is [[cold storage]]. This security measure is also referred to as being an air gap. For all practical purposes, this wallet is safe from all online threats, such as viruses and hackers. It is however still exposed to offline threats, such as [http://en.wikipedia.org/wiki/Hardware_keylogger hardware keyloggers], extortion, or people looking over your shoulder. A best practice is to keep the majority of your bitcoins in the offline wallet and only to use the online wallet for everyday expenses/earnings.

The below procedure may seem tedious, but remember that security almost always comes at the cost of convenience. When you deposit money at a bank, you let them worry about security. Bitcoins, however, are stored on '''your''' computer and that means '''you''' are fully responsible for securing them. The bitcoin ecosystem is still very young and unfortunately no user friendly tools for creating highly secure wallets have been developed yet (though some members of the Bitcoin community are [http://forum.bitcoin.org/?topic=7357.0 working hard at this]).

== How to deposit funds ==

# Set up a [http://www.wuala.com/en/bitcoin Wuala] account, or other cloud backup service of your choice.
# Create a strong and unique password offline (manually). This password should be at least 20 characters long; it should contain numbers, upper and lower case letters, and symbols. It should be as random as possible, ie it should look something like this: Zr%8qL03&cvwS9@05AatdP71. Never use this password elsewhere.
# '''Do not forget this password'''. Recite it several times a day. It is easy to overestimate your ability to remember a password several months in the future. To be on the safe side, write it down and store the piece of paper in a safety deposit box.
# Download [http://www.bitcoin.org/ Bitcoin Linux binary] and save it on a USB drive.
# Shut down your computer, and boot [http://www.ubuntu.com/ Ubuntu] (or Linux distribution of you choice) from a [http://www.ubuntu.com/download/ubuntu/download liveCD]. This will not affect your current operating system.
# '''Disconnect machine from the internet'''. Unplug any network cables and disable wireless. Verify that wireless is disabled in the icon on the upper right corner (Ubuntu). Double check that machine is disconnected by opening the web browser.
# Run bitcoin while disconnected to the internet. The client will show 0 connections and 0 blocks, but it will still generate a wallet.dat file and a bitcoin address.
# Encrypt your wallet using the strong and unique password from step 2 above. (Bitcoin Client > Settings > Encrypt wallet)
# Copy wallet.dat (found in hidden folder .bitcoin in your home directory) to USB drive.
# Save bitcoin address to a text file and copy it to USB drive.
# Shut down system and turn off computer. Before switching your computer on again, remove all power sources for about 1 minute. Physically remove battery from laptop.
# Backup encrypted wallet.dat file in several places:
#*Send it to your 5 best friends by email attachment and ask them to save it for you.
#*Save it on your Wuala account created in step 1.
#*Save it on several USB drives and CDs and store them in different geographic locations.
#Send bitcoins to the address saved on the USB drive. Double check in the [[Bitcoin Block Explorer|block explorer]] that they have been sent.

==How to retrieve funds ==

#Boot from Ubuntu liveCD, as in step 5 above.
#Insert USB drive.
#Run bitcoin client and close it again.
#Replace wallet.dat in ~/.bitcoin directory with wallet.dat from USB drive.
#Connect to the internet.
#Restart bitcoin client.
#Wait for blocks to download (optional).
#Send bitcoins.

==Notes==

*This procedure is only secure if you perform steps 1-13 in this '''exact order'''.

*Perform one or two trial runs of the above procedure with a few bitcents, and make sure that you know how to successfully retrieve them, before making a bulk transfer.

*Every time you retrieve bitcoins from your savings wallet, create a fresh savings wallet by repeating the above procedure, and send all your remaining savings balance there.

*There is more than one way to do it. Similar procedures have been suggested on the forums [http://forum.bitcoin.org/index.php?topic=17240.0 here] and [http://forum.bitcoin.org/?topic=5194.0 here].

*Beware that even savings wallets have limited lifetimes. New, backwards incompatible versions of bitcoin might come out in future, [http://en.wikipedia.org/wiki/Advanced_Encryption_Standard AES] might be broken, [http://en.wikipedia.org/wiki/Bit_rot bit rot] might destroy your wallets, etc. Update to fresh savings wallets every couple of years, or as needed.

* See [[How to import private keys]] for an alternative way of retrieve your coins.

==See Also==

* [[Cold storage]]
* [http://codinginmysleep.com/bitcoin-cold-storage-in-plain-english Bitcoin Cold Storage In Plain English] by David Perry

[[Category:Instructional]]
[[Category:Security]]

Talk:Wallet

2012-11-30T21:40:04Z

Jepo:

== file size ==

How much storage space does a wallet file tend to occupy? Does one need to allocate much disk space? How large a backup is one to consider? --[[User:Jepo|Jepo]] ([[User talk:Jepo|talk]]) 21:38, 30 November 2012 (GMT)

Talk:Wallet

2012-11-30T21:39:34Z

Jepo: /* size */ new section

How much storage space does a wallet file tend to occupy? Does one need to allocate much disk space? How large a backup is one to consider? --[[User:Jepo|Jepo]] ([[User talk:Jepo|talk]]) 21:38, 30 November 2012 (GMT)

== size ==

xx

Talk:Wallet

2012-11-30T21:39:01Z

Jepo: grammar

Talk:Wallet

2012-11-30T21:38:27Z

Jepo: Created page with "How much storage space does a wallet file tends to occupy? Does one need to allocate much disk space? How large a backup is one to consider? --~~~~"

How much storage space does a wallet file tends to occupy? Does one need to allocate much disk space? How large a backup is one to consider? --[[User:Jepo|Jepo]] ([[User talk:Jepo|talk]]) 21:38, 30 November 2012 (GMT)

Talk:Casascius physical bitcoins

2012-11-30T21:30:04Z

Jepo: Created page with "Has anyone tried to develop a technique to see the secret number inside a physical bitcoin, without opening it up? --~~~~"

Has anyone tried to develop a technique to see the secret number inside a physical bitcoin, without opening it up? --[[User:Jepo|Jepo]] ([[User talk:Jepo|talk]]) 21:30, 30 November 2012 (GMT)

Cold storage

2012-11-30T19:58:07Z

Jepo: link "physical bitcoin"

'''Cold storage''' in the context of Bitcoin refers to keeping a reserve of Bitcoins offline.

For example, a Bitcoin exchange typically offers an instant withdrawal feature, and might be a steward over hundreds of thousands of Bitcoins. To minimize the possibility that an intruder could steal the entire reserve in a security breach, the operator of the website follows a best practice by keeping the majority of the reserve in ''cold storage'', or in other words, not present on the web server or any other computer. The only amount kept on the server is the amount needed to cover anticipated withdrawals.

Methods of cold storage include keeping bitcoins:
* On a USB drive or other data storage medium in a safe place (e.g. safety deposit box, safe)
* On a [[paper wallet]]
* On a bearer item such as a [[physical bitcoin]].
* Online, but on encrypted media where the encryption key is offline.

'''Deep cold storage''' refers to keeping a reserve of Bitcoins offline, using a method that makes retrieving coins from storage significantly more difficult than sending them there. This could be done for safety's sake, such as to prevent theft or robbery.

Because Bitcoins can be sent to a wallet by anyone knowing the wallet address, it is trivial to put a wallet in cold storage but to keep a copy of the addresses needed to send funds to it.

A simple example of deep cold storage is opening a safety deposit box and putting a USB stick containing an encrypted wallet file in it. The public (sending) addresses can be used any time to send additional bitcoins to the wallet, but spending the bitcoins would require physical access to the box (in addition to knowledge of the encryption password).

Deep cold storage would typically be used for holding large amounts of bitcoins, or for a trustee holding bitcoins on behalf of others. In such a case, additional precautions should be taken beyond a simple example of a single safety deposit box.
* The box could be accessed by bank or maintenance personnel, so the contents of the box alone should not be sufficient to access the wallet.
* The box could be stolen or destroyed in a disaster, or the media could become unreadable, so the box should not contain the only copy of the wallet.
* The trustee could die or become incapacitated. If access to the wallet or knowledge of its location is lost, or encryption passwords are lost, the bitcoins are gone forever. Provisions should be made so that the box can be accessed by someone else as appropriate, including any encryption passwords.

== See also ==
* [[How to import private keys]]
* [[How to set up a secure offline savings wallet]]
* [http://codinginmysleep.com/bitcoin-cold-storage-in-plain-english Bitcoin Cold Storage In Plain English] by David Perry

[[Category:Introduction]]
[[Category:Security]]

Bitbills

2012-11-30T19:57:07Z

Jepo:

According to the product's announcement Bitbills are the first physical incarnation of bitcoins.

A Bitbill is a plastic card that holds the cryptographic key that will allow the face value amount of the card to be spent. The key is on a QR code embedded within the card such that it cannot be read without the card showing evidence of tampering. Additionally, the card has a hologram affixed to ensure that the card is not a counterfeit.

The intention is that the card will be left unopened and then can be treated as money by being acceptable at face value when making a transaction in-person at a retailer, for example. At any time, the card can be opened and the funds spent through the Bitcoin payment network. Once the card has been opened it will no longer be acceptable as payment anywhere else due to the fact that its [[private key]] has already been revealed.

At the time this article was created, the ability to spend a Bitbill required that a patch to the Bitcoin software be in place.

The cards come in denominations of 1 BTC, 5 BTC, 10 BTC and 20 BTC. Orders for the cards are accepted online and the only form of payment is Bitcoin.

The Bitbill launch was announced on May 9, 2011<ref>[http://www.bitcoin.org/smf/index.php?topic=7724.0 Introducing Bitbills!]</ref>.

As of May 15, 2012, Bitbills are no longer in production<ref>[http://bitbills.com/order Ordering Bitbills]</ref>.
==See Also==

* [[Digital currency]]

==External Links==

* [http://Bitbills.com Bitbills] web site

==References==

<references />

[[Category:Financial]]
[[Category:Digital_currencies]]
[[Category:Physical bitcoins]]

Casascius physical bitcoins

2012-11-30T19:53:45Z

Jepo:

[[Image:Casascius 25btc size compare.jpg|thumb|right|300px|Various views of Casascius coins]]
[[File:Physbitcoinkey.jpg|thumb|right|Redeemed Casascius coin]]
'''Casascius physical bitcoins''', also called '''Casascius coins''', are physical metal coins created by Bitcoin user [[User:Casascius|Casascius]] (Mike Caldwell, Sandy, Utah, USA) that contain an embedded piece of paper with digital Bitcoin value, covered by a tamper-resistant hologram. Casascius coins are available in 1, 10, 25, 100, and 1000 BTC increments. They can be purchased at Casascius's website, https://www.casascius.com (only Bitcoin accepted), or at http://www.MemoryDealers.com (PayPal and credit cards accepted).

The coins are designed such that they could be circulated in face-to-face transactions. The first person to redeem its [[private key]] gets the value on the coin, and afterwards, the coin no longer has any Bitcoin value. It is difficult or impossible to read the private key on the coin without damaging or destroying the hologram, which exposes a honeycomb-like tamper-evidence pattern when peeled.

The piece of paper inside each coin has a private key which forms the backing for the Bitcoin value represented by the coin. Redeeming the private key back into digital Bitcoins is currently available at [[MtGox]] (via the ''Add Funds - Redeem Private Key'' screen), as well as with a patched Bitcoin client.

Casascius coins are similar to [[Bitbills]] in that they are an object that contains a redemption code that serves as a bearer item for digital bitcoins.

There are 2 independent websites that track the status of all Casascius coins in circulation, based on information from the block chain:
* [[Casascius Bitcoin Analyzer]] (http://casascius.uberbills.com/)
* Casascius Physical Bitcoins Database (http://casascius.appspot.com/)

==Releases of Casascius coins==

===Original series 1 BTC coin===
* 1.125 inches in diameter
* Solid brass
* Year printed on coins: 2011
* Approximately 0.24 ounces
* Eight-digit "[[firstbits]]" inkjetted onto surface of hologram sticker
* First appeared in September 2011<ref>[http://bitcointalk.org/index.php?topic=41892.0 CASASCIUS PHYSICAL BITCOIN - In Stock Now!]</ref>.
* Private key: 22 character string inside the coin, the 256-bit private key is SHA256(string)
* Approximate number produced: {{formatnum:3500}} as of November 2011
* A spelling error can be found in the small lettering of the hologram: "CASACIUS" instead of "CASASCIUS"
* Casascius has stated that no more than {{formatnum:11000}} may be produced
* All {{formatnum:11000}} Bitcoin addresses pre-generated for the series have been published as a signed text file

===Second series 1 BTC coin===
[[Image:Casascius-series-2.jpg|thumb|right|200px|Second series 1 BTC Casascius coin]]
The hologram and the private key is different, the metal part of the coin is the same as the first series.
* 1.125 inches in diameter
* Solid brass
* Year printed on coins: 2011
* Approximately 0.24 ounces
* Denomination ("ONE BTC") appears on the hologram
* Eight-digit "firstbits" visible through a small transparent window that allows limited visibility of one side of the private key paper
* Private key: 30 character string inside the coin, the 256-private key is SHA256(string)
* First appeared in November 2011
* No spelling error in hologram

===10 BTC silver round===
* First available on Dec 1, 2011
* 39mm diameter
* 1 troy ounce .999 Fine Silver
* Uses second series holograms marked TEN BTC
* Comes in a clear plastic capsule
* Zeroes and ones on the back encode the message "Bitcoin: an idea too big to fail"

===25 BTC coin===
[[Image:Casascius 25btc.jpg|thumb|right|Casascius 25BTC coin]]
* 1.75 inches in diameter, about 3mm thick
* Gold-plated alloy
* Approximately 1.2 ounces
* Printed year: 2011
* Uses same holograms and private key scheme as original series 1 BTC coin
* First appeared in October 2011
* Zeroes and ones on the back encode the message "You asked for change, we gave you coins"

===100 BTC gold plated bar===
* Weight: 4.2oz
* Dimensions: 8cm x 4cm x 0.6cm
* Printed year: none
* Indented features: "100 BTC", Bitcoin logo, "gold plated bearer bar"
* Hologram: V1 or V2

===1000 BTC gold plated bar===
* Weight: 4.2oz
* Dimensions: 8cm x 4cm x 0.6cm
* Hologram: V1
* Printed year: none
* Lasered overprinting on the hologram to indicate the denomination
* This is a non-denominated bar that has been engraved with a 1000 BTC denomination. It is indented with the Bitcoin logo and the words "gold plated bearer bar" like the 100 BTC bar, but is not indented with a denomination. The denomination is applied via laser engraving.
* This item is presently listed for sale only through MemoryDealers.com

===1000 BTC 1 troy ounce gold coin===
* Available as of Dec 16, 2011
* Printed year: 2012
* Diameter: 30mm
* Special order item, 3 business day lead time
* Hologram: V1 with Bitcoin address lasered at top instead of inkjetted across middle
* Availability: Purchase from MemoryDealers.com, or directly from Casascius with BTC, or USD bank wire

== See also ==
* [[Mini private key format]]

== References ==
<references />

[[Category:Physical bitcoins]]

Physical bitcoin

2012-11-30T19:48:51Z

Jepo: "private key"

A special type of Bitcoin wallet that works as a bearer instrument that can be used to store bitcoins more safely or for trade offline.

A physical bitcoin holds the coin's public address and a hidden [[private key]]. The intention with a physical bitcoin is that the value of the coin has not and cannot be spent as long as the private key remains hidden, which is likely achieved through the use of a tamper-evident seal.

The earliest physical bitcoin, the [[Bitbills|Bitbill]], was shaped liked a credit card but that was then followed by the [[Casascius physical bitcoins|Casascius physical bitcoin]] which was affixed to a round medal. [[PrintCoins]] is creating cheques and denominated bills.

==See Also==

* List of [[:Category:Physical Bitcoins|Physical bitcoin]] sources.

[[Category:Digital currencies]]

Invoice address

2012-11-20T17:30:26Z

Jepo: /* Most addresses have a "private key" */

A '''Bitcoin address''', or simply '''address''', is an identifier of 34 alphanumeric characters (or less), beginning with the number 1 or 3, that represents a possible destination for a Bitcoin payment.
Addresses can be generated at no cost by any user of Bitcoin.
For example, using [[Bitcoin-Qt]], one can click "Get Address" and be assigned an address.
It is also possible to get a Bitcoin address using an account at an exchange or online wallet service.

An example of a Bitcoin address is ''37muSN5ZrukVTvyVh3mT5Zc5ew9L9CBare''.

==A Bitcoin address is like an e-mail address==
Like e-mail, you can send bitcoins to a person by sending bitcoins to one of their addresses. A person can have many different Bitcoin addresses and, for increased privacy, it is recommended that you use a unique address for each transaction. Most Bitcoin software and websites will help with this by generating a brand new address each time you perform a transaction. Some services provide a facility to request a new Bitcoin address for use with their service when desired.

When using a web site that accepts bitcoins or holds Bitcoin balances on your behalf, that website will assign a Bitcoin address to your account, so you can transfer funds into your account at the site. Very much unlike e-mail, this address may change every time funds come in so care should be taken when sending additional funds to a previously-used address. When you send Bitcoins to your account at a web site, they will usually be credited to your account at that web site after the transaction is [[confirmation|confirmed]].

==Addresses can be created offline==
Creating addresses can be done without an Internet connection and do not require any contact or registration with the Bitcoin network. The network only knows about an address when it is first used in a transaction. Because addresses can be created easily and at minimal cost, it is not uncommon to create temporary addresses that can be discarded if unused.

It is also possible to create large batches of addresses offline using other software tools. Generating batches of addresses is useful in several scenarios, such as e-commerce websites where a unique pre-generated address is dispensed to each customer who chooses a "pay with Bitcoin" option.

==Addresses are case sensitive and exact==
Bitcoin addresses are case-sensitive. Bitcoin addresses should be copied and pasted using the computer's clipboard wherever possible. If you hand-key a Bitcoin address, and each character is not transcribed exactly - including capitalization - the incorrect address will most likely be rejected by the Bitcoin software. You will have to check your entry and try again.

The probability that a mistyped address is accepted as being valid is 1 in 232, that is, approximately 1 in 4.29 billion.

==Address validation==
If you would like to validate a Bitcoin address in an application, it is advisable to use a method from [https://bitcointalk.org/index.php?topic=1026.0 this thread] rather than to just check for string length, allowed characters, or that the address starts with a 1.

==Most addresses have a "private key"==
For most addresses, there is a corresponding secret number known as a [[private key]] which is required for access to the funds assigned to that address.

When using a Bitcoin client, private keys are typically stored in the [[Wallet|wallet file]]. The private key has a special purpose - it is mathematically needed to create valid transactions that spend the funds originally sent to the address. If the private key to an address is lost (for example, in a hard drive crash, fire or other natural disaster), any associated Bitcoins are effectively lost forever.

==What's in an address==
Most Bitcoin addresses are 34 characters.
They consist of random digits and uppercase and lowercase letters, with the exception that the uppercase letter "O", uppercase letter "I", lowercase letter "l", and the number "0" are never used to prevent visual ambiguity.

Some Bitcoin addresses can be shorter than 34 characters and still be valid.
A significant percentage of Bitcoin addresses are only 33 characters, and some older addresses may be even shorter.
Every Bitcoin address stands for a number - somewhat like an account number. These shorter addresses are valid simply because they stand for numbers that happen to start with zeroes, and when the zeroes are omitted, the encoded address gets shorter.

Several of the characters inside a Bitcoin address are used as a checksum so that typographical errors can be automatically found and rejected.

==See Also==
* [[Technical background of Bitcoin addresses]]
* [[List of address prefixes]]
* [[Exit Address]]

[[Category:Vocabulary]]

Invoice address

2012-11-20T17:27:21Z

Jepo: /* Most addresses have a "private key" */ re-link "wallet"

A '''Bitcoin address''', or simply '''address''', is an identifier of 34 alphanumeric characters (or less), beginning with the number 1 or 3, that represents a possible destination for a Bitcoin payment.
Addresses can be generated at no cost by any user of Bitcoin.
For example, using [[Bitcoin-Qt]], one can click "Get Address" and be assigned an address.
It is also possible to get a Bitcoin address using an account at an exchange or online wallet service.

An example of a Bitcoin address is ''37muSN5ZrukVTvyVh3mT5Zc5ew9L9CBare''.

==A Bitcoin address is like an e-mail address==
Like e-mail, you can send bitcoins to a person by sending bitcoins to one of their addresses. A person can have many different Bitcoin addresses and, for increased privacy, it is recommended that you use a unique address for each transaction. Most Bitcoin software and websites will help with this by generating a brand new address each time you perform a transaction. Some services provide a facility to request a new Bitcoin address for use with their service when desired.

When using a web site that accepts bitcoins or holds Bitcoin balances on your behalf, that website will assign a Bitcoin address to your account, so you can transfer funds into your account at the site. Very much unlike e-mail, this address may change every time funds come in so care should be taken when sending additional funds to a previously-used address. When you send Bitcoins to your account at a web site, they will usually be credited to your account at that web site after the transaction is [[confirmation|confirmed]].

==Addresses can be created offline==
Creating addresses can be done without an Internet connection and do not require any contact or registration with the Bitcoin network. The network only knows about an address when it is first used in a transaction. Because addresses can be created easily and at minimal cost, it is not uncommon to create temporary addresses that can be discarded if unused.

It is also possible to create large batches of addresses offline using other software tools. Generating batches of addresses is useful in several scenarios, such as e-commerce websites where a unique pre-generated address is dispensed to each customer who chooses a "pay with Bitcoin" option.

==Addresses are case sensitive and exact==
Bitcoin addresses are case-sensitive. Bitcoin addresses should be copied and pasted using the computer's clipboard wherever possible. If you hand-key a Bitcoin address, and each character is not transcribed exactly - including capitalization - the incorrect address will most likely be rejected by the Bitcoin software. You will have to check your entry and try again.

The probability that a mistyped address is accepted as being valid is 1 in 232, that is, approximately 1 in 4.29 billion.

==Address validation==
If you would like to validate a Bitcoin address in an application, it is advisable to use a method from [https://bitcointalk.org/index.php?topic=1026.0 this thread] rather than to just check for string length, allowed characters, or that the address starts with a 1.

==Most addresses have a "private key"==
For most addresses, there is a corresponding secret number known as a [[private key]] that is required to spend funds previously sent to an address.

When using a Bitcoin client, private keys are typically stored in the [[Wallet|wallet file]]. The private key has a special purpose - it is mathematically needed to create valid transactions that spend the funds originally sent to the address. If the private key to an address is lost (for example, in a hard drive crash, fire or other natural disaster), any associated Bitcoins are effectively lost forever.

==What's in an address==
Most Bitcoin addresses are 34 characters.
They consist of random digits and uppercase and lowercase letters, with the exception that the uppercase letter "O", uppercase letter "I", lowercase letter "l", and the number "0" are never used to prevent visual ambiguity.

Some Bitcoin addresses can be shorter than 34 characters and still be valid.
A significant percentage of Bitcoin addresses are only 33 characters, and some older addresses may be even shorter.
Every Bitcoin address stands for a number - somewhat like an account number. These shorter addresses are valid simply because they stand for numbers that happen to start with zeroes, and when the zeroes are omitted, the encoded address gets shorter.

Several of the characters inside a Bitcoin address are used as a checksum so that typographical errors can be automatically found and rejected.

==See Also==
* [[Technical background of Bitcoin addresses]]
* [[List of address prefixes]]
* [[Exit Address]]

[[Category:Vocabulary]]

Invoice address

2012-11-20T17:25:26Z

Jepo: /* Addresses are case sensitive and exact */

A '''Bitcoin address''', or simply '''address''', is an identifier of 34 alphanumeric characters (or less), beginning with the number 1 or 3, that represents a possible destination for a Bitcoin payment.
Addresses can be generated at no cost by any user of Bitcoin.
For example, using [[Bitcoin-Qt]], one can click "Get Address" and be assigned an address.
It is also possible to get a Bitcoin address using an account at an exchange or online wallet service.

An example of a Bitcoin address is ''37muSN5ZrukVTvyVh3mT5Zc5ew9L9CBare''.

==A Bitcoin address is like an e-mail address==
Like e-mail, you can send bitcoins to a person by sending bitcoins to one of their addresses. A person can have many different Bitcoin addresses and, for increased privacy, it is recommended that you use a unique address for each transaction. Most Bitcoin software and websites will help with this by generating a brand new address each time you perform a transaction. Some services provide a facility to request a new Bitcoin address for use with their service when desired.

When using a web site that accepts bitcoins or holds Bitcoin balances on your behalf, that website will assign a Bitcoin address to your account, so you can transfer funds into your account at the site. Very much unlike e-mail, this address may change every time funds come in so care should be taken when sending additional funds to a previously-used address. When you send Bitcoins to your account at a web site, they will usually be credited to your account at that web site after the transaction is [[confirmation|confirmed]].

==Addresses can be created offline==
Creating addresses can be done without an Internet connection and do not require any contact or registration with the Bitcoin network. The network only knows about an address when it is first used in a transaction. Because addresses can be created easily and at minimal cost, it is not uncommon to create temporary addresses that can be discarded if unused.

It is also possible to create large batches of addresses offline using other software tools. Generating batches of addresses is useful in several scenarios, such as e-commerce websites where a unique pre-generated address is dispensed to each customer who chooses a "pay with Bitcoin" option.

==Addresses are case sensitive and exact==
Bitcoin addresses are case-sensitive. Bitcoin addresses should be copied and pasted using the computer's clipboard wherever possible. If you hand-key a Bitcoin address, and each character is not transcribed exactly - including capitalization - the incorrect address will most likely be rejected by the Bitcoin software. You will have to check your entry and try again.

The probability that a mistyped address is accepted as being valid is 1 in 232, that is, approximately 1 in 4.29 billion.

==Address validation==
If you would like to validate a Bitcoin address in an application, it is advisable to use a method from [https://bitcointalk.org/index.php?topic=1026.0 this thread] rather than to just check for string length, allowed characters, or that the address starts with a 1.

==Most addresses have a "private key"==
For most addresses, there is a corresponding secret number known as a [[private key]] that is required to spend funds previously sent to an address.

When using a Bitcoin client, private keys are typically stored in the [[wallet file]]. The private key has a special purpose - it is mathematically needed to create valid transactions that spend the funds originally sent to the address. If the private key to an address is lost (for example, in a hard drive crash, fire or other natural disaster), any associated Bitcoins are effectively lost forever.

==What's in an address==
Most Bitcoin addresses are 34 characters.
They consist of random digits and uppercase and lowercase letters, with the exception that the uppercase letter "O", uppercase letter "I", lowercase letter "l", and the number "0" are never used to prevent visual ambiguity.

Some Bitcoin addresses can be shorter than 34 characters and still be valid.
A significant percentage of Bitcoin addresses are only 33 characters, and some older addresses may be even shorter.
Every Bitcoin address stands for a number - somewhat like an account number. These shorter addresses are valid simply because they stand for numbers that happen to start with zeroes, and when the zeroes are omitted, the encoded address gets shorter.

Several of the characters inside a Bitcoin address are used as a checksum so that typographical errors can be automatically found and rejected.

==See Also==
* [[Technical background of Bitcoin addresses]]
* [[List of address prefixes]]
* [[Exit Address]]

[[Category:Vocabulary]]

Invoice address

2012-11-20T17:24:31Z

Jepo: /* Addresses are case sensitive and exact */

A '''Bitcoin address''', or simply '''address''', is an identifier of 34 alphanumeric characters (or less), beginning with the number 1 or 3, that represents a possible destination for a Bitcoin payment.
Addresses can be generated at no cost by any user of Bitcoin.
For example, using [[Bitcoin-Qt]], one can click "Get Address" and be assigned an address.
It is also possible to get a Bitcoin address using an account at an exchange or online wallet service.

An example of a Bitcoin address is ''37muSN5ZrukVTvyVh3mT5Zc5ew9L9CBare''.

==A Bitcoin address is like an e-mail address==
Like e-mail, you can send bitcoins to a person by sending bitcoins to one of their addresses. A person can have many different Bitcoin addresses and, for increased privacy, it is recommended that you use a unique address for each transaction. Most Bitcoin software and websites will help with this by generating a brand new address each time you perform a transaction. Some services provide a facility to request a new Bitcoin address for use with their service when desired.

When using a web site that accepts bitcoins or holds Bitcoin balances on your behalf, that website will assign a Bitcoin address to your account, so you can transfer funds into your account at the site. Very much unlike e-mail, this address may change every time funds come in so care should be taken when sending additional funds to a previously-used address. When you send Bitcoins to your account at a web site, they will usually be credited to your account at that web site after the transaction is [[confirmation|confirmed]].

==Addresses can be created offline==
Creating addresses can be done without an Internet connection and do not require any contact or registration with the Bitcoin network. The network only knows about an address when it is first used in a transaction. Because addresses can be created easily and at minimal cost, it is not uncommon to create temporary addresses that can be discarded if unused.

It is also possible to create large batches of addresses offline using other software tools. Generating batches of addresses is useful in several scenarios, such as e-commerce websites where a unique pre-generated address is dispensed to each customer who chooses a "pay with Bitcoin" option.

==Addresses are case sensitive and exact==
Bitcoin addresses are case-sensitive. Bitcoin addresses should be copied and pasted using the computer's clipboard wherever possible. If you hand-key a Bitcoin address, and each character is not transcribed exactly - including capitalization - the incorrect address will most likely be rejected by the Bitcoin client. You will have to check your entry and try again.

The probability that a mistyped address is accepted as being valid is 1 in 232, that is, approximately 1 in 4.29 billion.

==Address validation==
If you would like to validate a Bitcoin address in an application, it is advisable to use a method from [https://bitcointalk.org/index.php?topic=1026.0 this thread] rather than to just check for string length, allowed characters, or that the address starts with a 1.

==Most addresses have a "private key"==
For most addresses, there is a corresponding secret number known as a [[private key]] that is required to spend funds previously sent to an address.

When using a Bitcoin client, private keys are typically stored in the [[wallet file]]. The private key has a special purpose - it is mathematically needed to create valid transactions that spend the funds originally sent to the address. If the private key to an address is lost (for example, in a hard drive crash, fire or other natural disaster), any associated Bitcoins are effectively lost forever.

==What's in an address==
Most Bitcoin addresses are 34 characters.
They consist of random digits and uppercase and lowercase letters, with the exception that the uppercase letter "O", uppercase letter "I", lowercase letter "l", and the number "0" are never used to prevent visual ambiguity.

Some Bitcoin addresses can be shorter than 34 characters and still be valid.
A significant percentage of Bitcoin addresses are only 33 characters, and some older addresses may be even shorter.
Every Bitcoin address stands for a number - somewhat like an account number. These shorter addresses are valid simply because they stand for numbers that happen to start with zeroes, and when the zeroes are omitted, the encoded address gets shorter.

Several of the characters inside a Bitcoin address are used as a checksum so that typographical errors can be automatically found and rejected.

==See Also==
* [[Technical background of Bitcoin addresses]]
* [[List of address prefixes]]
* [[Exit Address]]

[[Category:Vocabulary]]

Base58Check encoding

2012-11-20T17:12:22Z

Jepo: link to WP

A modified Base 58 [http://en.wikipedia.org/wiki/Binary-to-text_encoding binary-to-text encoding] known as '''Base58Check''' is used for encoding [[Bitcoin address]]es.

More generically, Base58Check encoding is used for encoding byte arrays in Bitcoin into human-typable strings. A Bitcoin address is simply a Base58Check-encoded string with a 20-byte payload, the payload being the hash of the [[public key]] associated with the address.

The original Bitcoin client source code discusses the reasoning behind base58 encoding:

base58.h:
// Why base-58 instead of standard base-64 encoding?
// - Don't want 0OIl characters that look the same in some fonts and
// could be used to create visually identical looking account numbers.
// - A string with non-alphanumeric characters is not as easily accepted as an account number.
// - E-mail usually won't line-break if there's no punctuation to break at.
// - Doubleclicking selects the whole number as one word if it's all alphanumeric.

==Features of Base58Check==
Base58Check has the following features:
* An arbitrarily sized payload.
* A set of 58 alphanumeric symbols consisting of easily distinguished uppercase and lowercase letters (0OIl are not used)
* One byte of version/application information. Bitcoin addresses use 0x00 for this byte (future ones may use 0x05).
* Four bytes (32 bits) of SHA256-based error checking code. This code can be used to automatically detect and possibly correct typographical errors.
* An extra step for preservation of leading zeroes in the data.

==Creating a Base58Check string==
A Base58Check string is created from a version/application byte and payload as follows.
# Take the version/application byte and payload bytes, and concatenate them together (bytewise).
# Take the first four bytes of SHA256(SHA256(results of step 1))
# Concatenate the results of step 1 and the results of step 2 together (bytewise).
# Treating the results of step 3 - a series of bytes - as a single big-endian bignumber, convert to base-58 using normal mathematical steps (bignumber division) and the base-58 alphabet described below. The result should be normalized to not have any leading base-58 zeroes (character '1').
# The leading character '1', which has a value of zero in base58, is reserved for representing an entire leading zero '''byte''', as when it is in a leading position, has no value as a base-58 symbol. There can be one or more leading '1's when necessary to represent one or more leading zero bytes. Count the number of leading zero bytes that were the result of step 3 (for old Bitcoin addresses, there will always be at least one for the version/application byte; for new addresses, there will never be any). Each leading zero byte shall be represented by its own character '1' in the final result.
# Concatenate the 1's from step 5 with the results of step 4. '''This is the Base58Check result.'''

==Encoding a Bitcoin address==
A Bitcoin address is based on any [[ECDSA]] [[secp256k1]] public/private [[key pair]].

A Bitcoin address is the Base58Check encoding of the hash of the associated [[script]]. Specifically, it is Base58Check(5,[[RIPEMD160]]([[SHA256]]([[script]]))), with the following constraints:
* [[RIPEMD160]] and [[SHA256]] in this case are always exactly 20 and 32 unsigned bytes respectively. These are big-endian (most significant byte first). (Beware of [[bignumber]] implementations that clip leading 0x00 bytes, or prepend extra 0x00 bytes to indicate sign - your code must handle these cases properly or else you may generate valid-looking addresses which can be sent to, but cannot be spent from - which would lead to the permanent loss of coins.)
* 0 refers to the version/application byte.

Because of the 0x05 version/application byte, Bitcoin addresses always start with the digit '3'.

==Encoding a private key==
Base58Check encoding is also used for encoding [[private key]]s in the [[Wallet Import Format]]. This is formed exactly the same as a Bitcoin address, except that 0x80 is used for the version/application byte, and the payload is 32 bytes instead of 20 (a private key in Bitcoin is a single 32-byte unsigned big-endian integer). Such encodings will always yield a 51-character string that starts with '5', or more specifically, either '5H', '5J', or '5K'.

==Base58 symbol chart==
The Base58 symbol chart used in Bitcoin is specific to the Bitcoin project and is not intended to be the same as any other Base58 implementation used outside the context of Bitcoin.
{| class="wikitable"
|-
!Value
!Character
!Value
!Character
!Value
!Character
!Value
!Character
|-
|0
|1
|1
|2
|2
|3
|3
|4
|-
|4
|5
|5
|6
|6
|7
|7
|8
|-
|8
|9
|9
|A
|10
|B
|11
|C
|-
|12
|D
|13
|E
|14
|F
|15
|G
|-
|16
|H
|17
|J
|18
|K
|19
|L
|-
|20
|M
|21
|N
|22
|P
|23
|Q
|-
|24
|R
|25
|S
|26
|T
|27
|U
|-
|28
|V
|29
|W
|30
|X
|31
|Y
|-
|32
|Z
|33
|a
|34
|b
|35
|c
|-
|36
|d
|37
|e
|38
|f
|39
|g
|-
|40
|h
|41
|i
|42
|j
|43
|k
|-
|44
|m
|45
|n
|46
|o
|47
|p
|-
|48
|q
|49
|r
|50
|s
|51
|t
|-
|52
|u
|53
|v
|54
|w
|55
|x
|-
|56
|y
|57
|z
|}

The algorithm for encoding address_byte_string (consisting of 0x01 + hash + 4-byte_check_code) is

code_string = "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz"
x = convert_bytes_to_big_integer(hash_result)

output_string = ""

while(x > 0)
{
(x, remainder) = divide(x, 58)
output_string.append(code_string[remainder])
}

repeat(number_of_leading_zero_bytes_in_hash)
{
output_string.append(code_string[0]);
}

output_string.reverse();

==Version bytes==
Here are some common version bytes:

{| class="wikitable"
|-
!Decimal version
!Leading symbol
!Use
|-
|0
|1
|Bitcoin pubkey hash
|-
|5
|3
|Bitcoin script hash
|-
|21
|4
|Bitcoin (compact) public key (proposed)
|-
|52
|M or N
|Namecoin pubkey hash
|-
|128
|5
|Private key
|-
|111
|m or n
|Bitcoin testnet pubkey hash
|-
|196
|2
|Bitcoin testnet script hash
|}
[[List of address prefixes]] is a more complete list.

== Source ==
https://github.com/bitcoin/bitcoin/blob/master/src/base58.h

== Relevant functions in source code ==
* inline string EncodeBase58Check(const vector<unsigned char>& vchIn)
* inline bool DecodeBase58Check(const char* psz, vector<unsigned char>& vchRet)
* inline bool DecodeBase58Check(const string& str, vector<unsigned char>& vchRet)

[[Category:Technical]]

Wallet

2012-11-20T17:01:00Z

Jepo: /* Bitcoin Qt */

A Bitcoin '''wallet''' is a file that contains a collection of private keys.

=== Bitcoin Qt ===

The original Bitcoin client wallet file is named '''wallet.dat''' and contains<ref>[https://bitcointalk.org/index.php?topic=4448.0 Wallet import/export: bitkeys format]</ref>:

* keypairs for each of your [[address|addresses]]
* transactions done from/to your addresses
* user preferences
* default key
* reserve keys
* [[Accounts_explained|accounts]]
* a version number
* [[Key pool]]
* Since 0.3.21: information about the current best chain, to be able to rescan automatically when restoring from a backup.

The data file for the wallet is wallet.dat and is located in the [[data directory|Bitcoin data directory]].

It is intended that a wallet be used on only one installation of Bitcoin at a time. Attempting to clone a wallet for use on multiple computers will result in "weird behavior"<ref>[http://forum.bitcoin.org/index.php?topic=5324.msg77896#msg77896 Multiple instance of bitcoin with the same wallet]</ref>.

The format of this file is Berkeley DB. Tools that can manipulate wallet files include [[pywallet]].

=== Armory ===

The Armory client uses a custom [http://bitcoinarmory.com/index.php/armory-wallet-files binary wallet format].

=== Blockchain.info ===

Blockchain.info use a plain text JSON wallet format documented [https://blockchain.info/wallet/wallet-format here]. Private keys Keys are stored in base58.

=== Multibit ===

Multibit uses the BitcoinJ [http://code.google.com/p/protobuf/ protobuf] wallet file.

==See Also==

* [[Securing your wallet]]
* [[EWallet]]
* [[Deterministic Wallet]]
==References==
<references />

Mt. Gox

2012-11-16T20:17:23Z

Jepo: /* Redeemable Code */ "coupon"

'''MtGox''', called "Mount Gox" or "MTGOX", has been the most widely used bitcoin [[currency exchange]] market<ref>2011-06-07 on #bitcoin-otc: "MagicalTux: you could use the count of users on mtgox (went over 30k recently)"</ref> since it was started, and remains the largest in terms of popularity and volume.

A registrant on MtGox has at least two sub-accounts: one for bitcoins (BTC), and one for US dollars (USD or MTGUSD) or other national currency. Bitcoins are bought using funds from the trader's national currency account, and the proceeds from the sale of bitcoins are deposited into the same account. Trading must always involve bitcoins as trading between different national currencies is not offered.

Trades on Mt. Gox's execute from balances on deposit with the exchange which in turn makes trading on the market instantaneous, compared to some other Bitcoin markets where a subsequent settlement occurs manually between the trading partners. The disadvantage of this is that a third party must be trusted with keeping the money safe.

MtGox was originally started by Jed McCaleb in July 2010, and was sold to [[Tibanne Co.]] in Japan in March 2011. It is currently operated by Tibanne Co., managed by Mark Karpeles (MagicalTux).

==Trading==
===Buying and selling===

Buying and selling Bitcoins is simple. A buy order is executed partially or in full when the price bid can be matched against a sell order that is at or below the bid amount. A sell order is executed partially or in full when the price asked can be matched against a buy order that is at or above the ask amount. Orders that cannot be matched immediately remain in the orderbook.

Unfunded orders do not appear in the order book, but are automatically readded if a deposit is credited. For example, Mt. Gox allows the entry of a "buy" order even if the account has insufficient funds. If possible, Mt. Gox will execute a portion of the order if it can be partially funded. If a deposit is later credited and the deposit resolves the insufficient funds status of an outstanding order, the order will be immediately activated, and if possible, executed.

===Fees===

Mt. Gox charges a trading fee of up to 0.6% from each party of successful trades made through the market. The fee appears in the account history next to each trade. The trading fee is discounted for larger customers based on volume, which is calculated as a sliding window over the last 720 hours (30 days).

The fees are, by default, subtracted from the proceeds of each trade (e.g., a buy of 1.0 BTC will add to the account balance 0.994 BTC when the exchange fee is 0.6%). An account setting will allow fees to be added to the purchase amount instead (e.g., buying 1.0 BTC at $5 will cost about $5.03 when the exchange fee is 0.6%).

==Adding Funds==

===BTC===
There are no fees incurred when transferring bitcoins to a Mt. Gox account.

Funds are available once [[confirmation|confirmed]] (6 blocks)<ref>[http://www.bitcoin.org/smf/index.php?topic=3851.msg55220#msg55220 How long does it take to Deposit bitcoins to MtGox?]</ref>, a process that can take roughly an hour.

The deposit address is presented along with a QR code that can be scanned with a mobile. This address does not change with each deposit request.

The Add Bitcoins function experiences issues with some browser ad-blocking utilities even though no advertisements are displayed on the website.

====Redeemable Code====

Bitcoins from another Mt. Gox user sent by Mt. Gox [[redeemable code]] (A.K.A. "coupon") may be deposited and will be available for trading immediately.

===Dwolla===

Dwolla is among the fastest and least expensive methods for adding funds from the United States of America to a Mt. Gox account. The transaction fee on [[Dwolla]] is merely $0.25. The process is automated and the funds become available for trading within an hour<ref>[http://forum.bitcoin.org/index.php?topic=15107.msg205622#msg205622 Dwolla to Mt. Gox vs. Dwolla to TradeHill]</ref>.

===OKPay===

OKPay may be used for depositing funds to USD, EUR, GBP, CHF, and RUB<ref>[https://support.mtgox.com/entries/21034626-okpay OKPAY]</ref>.

===Cash Deposit===

====U.S. (USD)====
* BitInstant - Cash (U.S. dollars) may be deposited at any of thousands of banks, 7-11, Walmart, CVS, Moneygram and more that [[BitInstant]] uses to transfer funds to your Mt. Gox account.

====Brazil (BRL)====
* BitInstant - Cash (Brazilian real) may be deposited using Boleto or through Banco Recomendito.

====Brazil (BRL)====
* BitInstant - Cash (Russian rubles) may be deposited using QIWI or Cyberplat

====UK (GBP)====
* Barclays - Cash (British pound sterling) may be deposited at any Barclays location. There is a 1.5% fee on deposits made with this method<ref>[https://mtgox.com/press_release_20120806.html Introducing a new 1.5% fee on Barclays cash deposit]</ref>.

===Bank Wire===

====International USD====
Funds in USD may be wired to the exchange's bank in Japan. Each wire is subject to a per-wire fee plus any intermediate fees.

====International Wire====

An account can be configured with a wallet for each of the currencies that the exchange supports<ref>[https://mtgox.zendesk.com/entries/20413328-mt-gox-opens-15-new-currency-markets Mt.Gox Opens 15 New Currency Markets]</ref>. When a wire is received in one of these currencies, that account will be credited.

* USD - U.S. Dollar
* EUR - Euro (SEPA or Int'l wire)
* CAD - Canadian Dollar
* GBP - British Pound (Domestic or Int'l wire)
* CHF - Swiss Francs
* RUB - Russian Rubles
* AUD - Australian Dollars
* SEK - Swedish Krona
* DKK - Danish Krona
* HKD - Hong Kong Dollars
* PLN - Polish Zloty (Domestic or Int'l wire)
* CNY - Chinese Yuan
* SGD - Singapore Dollars
* TBH - Thai Baht
* NZD - New Zealand Dollars
* JPY - Japanese Yen (Domestic or Int'l wire)

====AurumXChange USD, EUR and CAD====

Funds may be wired to [[AurumXChange Company]] as USD, EUR or CAD (the latter two of which would then be exchanged into USD) for for purchase of a Mt. Gox USD [[redeemable code]] (voucher). Other digital currencies such as [[Liberty Reserve]] can be converted for transfer to Mt. Gox as well. The redeemable code provided is then used to load USD funds into an account with Mt. Gox.

===Direct Deposit===
====EU====

Funds in EUR may be added using SEPA Direct Debit for free, with funds convert to USD at the current ECB rate at the time the funds are received<ref>[http://www.bitcoin.org/smf/index.php?topic=5461.0 MTGox: Euro deposits]</ref>.

====U.S.====

Mt. Gox doesn't directly support an ACH-based (direct deposit) deposit method. Dwolla supports ACH-based fund transfers and those funds can then be deposited with Mt. Gox.

====UK====

Funds may be sent as a GBP direct deposit free of charge.

====Australia====

Funds may be sent using direct deposit (BPay) for a AU$2.00 per-deposit fee. The funds will be converted to USD at the current rate.

==Withdrawing Funds==

MtGox imposes a $1,000 USD limit for withdrawals per 24 hours and a $10,000 USD limit for withdrawals per month with most non-verified accounts. Bitcoins withdrawn are counted toward this limit as well and the USD value is calculated at the market rate at the time of the attempted withdrawal. Customers that have been Verified have higher limits and customers that have Trusted status have limits even higher<ref>[http://bitcoin.stackexchange.com/questions/2442/mtgox-trusted-vs-verified MtGox - trusted vs verified]</ref>. Any [[MtGox#Transfers_to_Other_Customers|account-to-account transfers]] made also count toward this limit as well.

Requests for higher withdrawal limits may be submitted by email
* For higher limits for withdrawal of USD funds, email: aml@mtgox.com
* For higher limits for withdrawal of BTC funds, email: btcupd@mtgox.com

See the [[MtGox#AML|AML]] section regarding verification levels for AML purposes.

===Dwolla===

[[Dwolla]] is among the fastest and least expensive methods for withdrawing USD funds from a Mt. Gox account. The transaction fee to do so is just $0.25.
[[Dwolla]] withdrawals are processed every hour during business hours (Japan time) and every 12 hours on weekends.

As of 25 May 2012, MtGox requires account holders to be "verified (level 1) - 'see below'" to withdraw via Dwolla. <ref>https://support.mtgox.com/entries/21503347-new-aml-policy-for-all-dwolla-users</ref>

The status of the withdrawal request will show one of the following status codes:

* Preparing: System is running checks to see if the transfer can be executed.
* Confirmed: Transfer can be executed and is pending in queue.
* Todo: Transfer is near the top of the queue and will be executed soon.
* Processed: Transfer has been processed.

===BTC===

Bitcoins may be withdrawn at no charge.

A [[green address]] option is available though this type of transaction could experience a delay if the exchange's wallet funding level for green address transactions is insufficient. The withdrawal form also offers an "open transaction" option which forces the transaction to go through the blockchain. If the recipient of a BTC withdrawal happens to also be from Mt. Gox's [[EWallet]], then that transfer would occur instantly and the transaction would not be broadcast to the Bitcoin network. This "open transaction" option forces a withdrawal to be broadcast to the Bitcoin network.

====Redeemable Code====

Bitcoins to another Mt. Gox account may be sent by Mt. Gox [[redeemable code]].

===Redeemable Code (Currency)===

Funds may be withdrawn by sending a Mt. Gox redeemable code (voucher) to another party.

The denominated of the code will be for the currency of the account's wallet that is active when the withdrawal request is inititiated (e.g., MTGUSD, MTGEUR, MTGAUD, MTGCAD, etc.)

Following are some of the services which accept a Mt. Gox redeemable code.

====AurumXChange USD, EUR and CAD====

Funds sent to [[AurumXChange Company]] can then be wired to a USD, EUR or CAD bank account or they can be converted to another digital currency, such as Liberty Reserve.

====BitInstant====

USD funds sent to to [[BitInstant]] can then be transferred further through their service.

===Direct Deposit===
====U.S.====

There is currently no option for withdrawing funds through a direct deposit bank transaction. Funds withdrawn to Dwolla may then, in turn, be withdrawn with bank funds deposited as an ACH transaction.

====EU====

You may withdraw any amount as a direct deposit to your bank. There is a 2% fee on these withdrawals. Contact the exchange by e-mail for this service.

====Australia====

A per-withdrawal fee (2,000 JPY) is subtracted and the remaining amount is sent via international wire in the chosen currency. If not AUD then an exchange fee of 2.5% will be charged.

===International Wire===

To any IBAN, SWIFT/BIC and ABA routable bank<ref>[http://www.facebook.com/MtGox/posts/343372689080478 Mt.Gox now offers international wire transfer to all US Banks]</ref>. Fee applies.

==Transfers to Other Customers==

Mt. Gox funds, either USD or BTC, may be sent to another Mt. Gox customer using a redeemable Mt. Gox code (voucher).

==Customer Service==

The preferred method for obtaining service is to place a request through the exchange's [https://mtgox.zendesk.com help desk]. Another method is to send e-mail with the request.

==Wallet/Banking==

An account at this exchange can be considered to be an [[eWallet]]. This service also offers [[:Category:ECommerce|eCommerce]] merchant [https://mtgox.com/merch/about payment services].

==Security Center==

The Security Center allows an account to be secured through the use of one or more One Time Password (OTP) solutions such as what YubiKey and Google Authenticator offer. Features can be protected where the OTP must be provided for each action and are configured independently.

For example, a typical configuration is to set OTP as being required for both withdrawals and security center changes but not for login. With that configuration, the worst damage that can happen from a compromised account or session would be that bitcoins would be bought or sold (though they could also be bought and sold over and over until funds are depleted).

* Login - The OTP must be provided for each login.
* Withdraw - The OTP must be provided for each withdrawal request.
* Security - The OTP must be provided during each configuration change to be performed.

==AML==

Varying degrees of verification will allow for greater per-day and per-month total amounts to be withdrawn<ref>[http://support.mtgox.com/entries/20919111-aml-account-statuses AML Account Statuses]</ref>.

===Unverified (Level 0)===

Designed for basic users, consumers and Bitcoin enthusiasts where 10,000 USD (monthly) is enough for most needs.

===Verified (Level 1)===

The "verified" status is designed for active traders and/or small companies.

===Trusted (Level 2)===

The “trusted” status is designed for day traders, professionals, and companies.

==API==

Mt Gox offers an [[MtGox/API|API]] which can be used to automate operations.

==Data Services==

===Web===
* Bitstock live watcher for trades, depth, history [http://bitstock.info bitstock.info] (Websockets browser required)
* [[Bitcoin Charts]]
* Clark Moody's [[Real Time Bitcoin Market Data]] including Ticker, Order Book and Time Sales (Websockets browser support required)
* [[MtGox Live]] (Websockets browser support required)
* [[Bitcoin Arbitrage Opportunities]] (Websockets browser support required)
* [[Bitcoin Prices]] market rates in multiple currencies

===Windows===
* [[Sierra Chart MtGox Bridge]] trading and charting tool.
* [[ToyTrader]] command line trading tool

===Mac OS X===
* [[BitTicker]] for Mac OS X
* [http://sneak.datavibe.net/20110613/mtgoxwatcher MtGox Watcher] for Mac OS X

===Mobile===
* [[BitcoinX]] mobile app with bid, ask and 24 hour history. For Android
* [[MtGox Live]] Bitcoin Trader with buy, sell, send, chart and depth for Android and iOS

=== firefox addon ===
* [https://github.com/joric/mtgox-ticker] firefox ticker addon

===Linux===
* [http://www.goxsh.info goxsh] command line ticker / depth chart
* [https://github.com/3M3RY/tulpenmanie tulpenmanie] graphical trading platform

==E-Commerce==

Online sellers can accept bitcoins for payment using the Mt. Gox's E-commerce Solution, which is an interface to the exchange's [[MtGox/API/HTTP/v1#Merchant_System|Merchant System API]].

==History==
The exchange went online on July 18, 2010.<ref>[http://www.bitcoin.org/smf/index.php?topic=444.0 MtGox announcement on forum]</ref>

On October 10, 2010 the exchange switched from [[PayPal]] to Liberty Reserve as the main funding option as a result of this attack. Former PayPal customers still had the possibility to withdraw their USD using alternative methods.

On March 6th, 2011 ownership of the exchange changed hands<ref>[http://www.bitcoin.org/smf/index.php?topic=4187.0 Mtgox is changing owners]</ref>. Tibanne publishes their [http://legal.tibanne.com/docs/20110801_company_certificate.pdf company certificate] from the Japanese government.

On June 19, 2011 the service experienced a significant security breach<ref>[https://support.mtgox.com/entries/20224998-huge-bitcoin-sell-off-due-to-a-compromised-account-rollback Huge Bitcoin sell off due to a compromised account - rollback]</ref>. The incident caused a selloff down to BTC/USD of $0.01 due to fraudulent trading. The site was disabled and all trading following the point that fraudulent trading began was rolled back. Complicating this breach was the release of a list of the exchange's accounts including username, email address and a password hash, which forced the exchange to implement an account recovery method for customers to regain control of their accounts.

In July, 2011 it was observed that the exchange no longer allows new registrations to occur without having a valid e-mail address.

On July 19, 2011 a press release announced that MtGox had acquired [[MtGox Live]].<ref>[https://mtgox.com/press_release_20110719.html World's Leading Bitcoin Exchange, Mt.Gox, acquires MtGoxLive.com]</ref>

Announced on March 6, 2012 was the Merchant Solution and API<ref>[https://mtgox.com/press_release_20120306.html Mt.Gox launches the definitive bitcoin checkout solution]</ref>

==See Also==

* [[Buying bitcoins]]
* [[Selling bitcoins]]
* [[MtGox/API|API]]

==External Links==

* [https://mtgox.com MT. Gox exchange] website
* [https://mtgox.com/merch/about Mt. Gox Merchant Services]
* [https://mtgox.zendesk.com Customer Service Help Desk]

==References==
<references/>

[[Category:Exchanges]]
[[Category:eWallets]]
[[Category:Shopping Cart Interfaces]]
[[ru:MtGox]]

Mt. Gox

2012-11-14T03:19:57Z

Jepo: /* Dwolla */ US only

'''MtGox''', called "Mount Gox" or "MTGOX", has been the most widely used bitcoin [[currency exchange]] market<ref>2011-06-07 on #bitcoin-otc: "MagicalTux: you could use the count of users on mtgox (went over 30k recently)"</ref> since it was started, and remains the largest in terms of popularity and volume.

A registrant on MtGox has at least two sub-accounts: one for bitcoins (BTC), and one for US dollars (USD or MTGUSD) or other national currency. Bitcoins are bought using funds from the trader's national currency account, and the proceeds from the sale of bitcoins are deposited into the same account. Trading must always involve bitcoins as trading between different national currencies is not offered.

Trades on Mt. Gox's execute from balances on deposit with the exchange which in turn makes trading on the market instantaneous, compared to some other Bitcoin markets where a subsequent settlement occurs manually between the trading partners. The disadvantage of this is that a third party must be trusted with keeping the money safe.

MtGox was originally started by Jed McCaleb in July 2010, and was sold to [[Tibanne Co.]] in Japan in March 2011. It is currently operated by Tibanne Co., managed by Mark Karpeles (MagicalTux).

==Trading==
===Buying and selling===

Buying and selling Bitcoins is simple. A buy order is executed partially or in full when the price bid can be matched against a sell order that is at or below the bid amount. A sell order is executed partially or in full when the price asked can be matched against a buy order that is at or above the ask amount. Orders that cannot be matched immediately remain in the orderbook.

Unfunded orders do not appear in the order book, but are automatically readded if a deposit is credited. For example, Mt. Gox allows the entry of a "buy" order even if the account has insufficient funds. If possible, Mt. Gox will execute a portion of the order if it can be partially funded. If a deposit is later credited and the deposit resolves the insufficient funds status of an outstanding order, the order will be immediately activated, and if possible, executed.

===Fees===

Mt. Gox charges a trading fee of up to 0.6% from each party of successful trades made through the market. The fee appears in the account history next to each trade. The trading fee is discounted for larger customers based on volume, which is calculated as a sliding window over the last 720 hours (30 days).

The fees are, by default, subtracted from the proceeds of each trade (e.g., a buy of 1.0 BTC will add to the account balance 0.994 BTC when the exchange fee is 0.6%). An account setting will allow fees to be added to the purchase amount instead (e.g., buying 1.0 BTC at $5 will cost about $5.03 when the exchange fee is 0.6%).

==Adding Funds==

===BTC===
There are no fees incurred when transferring bitcoins to a Mt. Gox account.

Funds are available once [[confirmation|confirmed]] (6 blocks)<ref>[http://www.bitcoin.org/smf/index.php?topic=3851.msg55220#msg55220 How long does it take to Deposit bitcoins to MtGox?]</ref>, a process that can take roughly an hour.

The deposit address is presented along with a QR code that can be scanned with a mobile. This address does not change with each deposit request.

The Add Bitcoins function experiences issues with some browser ad-blocking utilities even though no advertisements are displayed on the website.

====Redeemable Code====

Bitcoins from another Mt. Gox user sent by Mt. Gox [[redeemable code]] may be deposited and will be available for trading immediately.

===Dwolla===

Dwolla is among the fastest and least expensive methods for adding funds from the United States of America to a Mt. Gox account. The transaction fee on [[Dwolla]] is merely $0.25. The process is automated and the funds become available for trading within an hour<ref>[http://forum.bitcoin.org/index.php?topic=15107.msg205622#msg205622 Dwolla to Mt. Gox vs. Dwolla to TradeHill]</ref>.

===OKPay===

OKPay may be used for depositing funds to USD, EUR, GBP, CHF, and RUB<ref>[https://support.mtgox.com/entries/21034626-okpay OKPAY]</ref>.

===Cash Deposit===

====U.S. (USD)====
* BitInstant - Cash (U.S. dollars) may be deposited at any of thousands of banks, 7-11, Walmart, CVS, Moneygram and more that [[BitInstant]] uses to transfer funds to your Mt. Gox account.

====Brazil (BRL)====
* BitInstant - Cash (Brazilian real) may be deposited using Boleto or through Banco Recomendito.

====Brazil (BRL)====
* BitInstant - Cash (Russian rubles) may be deposited using QIWI or Cyberplat

====UK (GBP)====
* Barclays - Cash (British pound sterling) may be deposited at any Barclays location. There is a 1.5% fee on deposits made with this method<ref>[https://mtgox.com/press_release_20120806.html Introducing a new 1.5% fee on Barclays cash deposit]</ref>.

===Bank Wire===

====International USD====
Funds in USD may be wired to the exchange's bank in Japan. Each wire is subject to a per-wire fee plus any intermediate fees.

====International Wire====

An account can be configured with a wallet for each of the currencies that the exchange supports<ref>[https://mtgox.zendesk.com/entries/20413328-mt-gox-opens-15-new-currency-markets Mt.Gox Opens 15 New Currency Markets]</ref>. When a wire is received in one of these currencies, that account will be credited.

* USD - U.S. Dollar
* EUR - Euro (SEPA or Int'l wire)
* CAD - Canadian Dollar
* GBP - British Pound (Domestic or Int'l wire)
* CHF - Swiss Francs
* RUB - Russian Rubles
* AUD - Australian Dollars
* SEK - Swedish Krona
* DKK - Danish Krona
* HKD - Hong Kong Dollars
* PLN - Polish Zloty (Domestic or Int'l wire)
* CNY - Chinese Yuan
* SGD - Singapore Dollars
* TBH - Thai Baht
* NZD - New Zealand Dollars
* JPY - Japanese Yen (Domestic or Int'l wire)

====AurumXChange USD, EUR and CAD====

Funds may be wired to [[AurumXChange Company]] as USD, EUR or CAD (the latter two of which would then be exchanged into USD) for for purchase of a Mt. Gox USD [[redeemable code]] (voucher). Other digital currencies such as [[Liberty Reserve]] can be converted for transfer to Mt. Gox as well. The redeemable code provided is then used to load USD funds into an account with Mt. Gox.

===Direct Deposit===
====EU====

Funds in EUR may be added using SEPA Direct Debit for free, with funds convert to USD at the current ECB rate at the time the funds are received<ref>[http://www.bitcoin.org/smf/index.php?topic=5461.0 MTGox: Euro deposits]</ref>.

====U.S.====

Mt. Gox doesn't directly support an ACH-based (direct deposit) deposit method. Dwolla supports ACH-based fund transfers and those funds can then be deposited with Mt. Gox.

====UK====

Funds may be sent as a GBP direct deposit free of charge.

====Australia====

Funds may be sent using direct deposit (BPay) for a AU$2.00 per-deposit fee. The funds will be converted to USD at the current rate.

==Withdrawing Funds==

MtGox imposes a $1,000 USD limit for withdrawals per 24 hours and a $10,000 USD limit for withdrawals per month with most non-verified accounts. Bitcoins withdrawn are counted toward this limit as well and the USD value is calculated at the market rate at the time of the attempted withdrawal. Customers that have been Verified have higher limits and customers that have Trusted status have limits even higher<ref>[http://bitcoin.stackexchange.com/questions/2442/mtgox-trusted-vs-verified MtGox - trusted vs verified]</ref>. Any [[MtGox#Transfers_to_Other_Customers|account-to-account transfers]] made also count toward this limit as well.

Requests for higher withdrawal limits may be submitted by email
* For higher limits for withdrawal of USD funds, email: aml@mtgox.com
* For higher limits for withdrawal of BTC funds, email: btcupd@mtgox.com

See the [[MtGox#AML|AML]] section regarding verification levels for AML purposes.

===Dwolla===

[[Dwolla]] is among the fastest and least expensive methods for withdrawing USD funds from a Mt. Gox account. The transaction fee to do so is just $0.25.
[[Dwolla]] withdrawals are processed every hour during business hours (Japan time) and every 12 hours on weekends.

As of 25 May 2012, MtGox requires account holders to be "verified (level 1) - 'see below'" to withdraw via Dwolla. <ref>https://support.mtgox.com/entries/21503347-new-aml-policy-for-all-dwolla-users</ref>

The status of the withdrawal request will show one of the following status codes:

* Preparing: System is running checks to see if the transfer can be executed.
* Confirmed: Transfer can be executed and is pending in queue.
* Todo: Transfer is near the top of the queue and will be executed soon.
* Processed: Transfer has been processed.

===BTC===

Bitcoins may be withdrawn at no charge.

A [[green address]] option is available though this type of transaction could experience a delay if the exchange's wallet funding level for green address transactions is insufficient. The withdrawal form also offers an "open transaction" option which forces the transaction to go through the blockchain. If the recipient of a BTC withdrawal happens to also be from Mt. Gox's [[EWallet]], then that transfer would occur instantly and the transaction would not be broadcast to the Bitcoin network. This "open transaction" option forces a withdrawal to be broadcast to the Bitcoin network.

====Redeemable Code====

Bitcoins to another Mt. Gox account may be sent by Mt. Gox [[redeemable code]].

===Redeemable Code (Currency)===

Funds may be withdrawn by sending a Mt. Gox redeemable code (voucher) to another party.

The denominated of the code will be for the currency of the account's wallet that is active when the withdrawal request is inititiated (e.g., MTGUSD, MTGEUR, MTGAUD, MTGCAD, etc.)

Following are some of the services which accept a Mt. Gox redeemable code.

====AurumXChange USD, EUR and CAD====

Funds sent to [[AurumXChange Company]] can then be wired to a USD, EUR or CAD bank account or they can be converted to another digital currency, such as Liberty Reserve.

====BitInstant====

USD funds sent to to [[BitInstant]] can then be transferred further through their service.

===Direct Deposit===
====U.S.====

There is currently no option for withdrawing funds through a direct deposit bank transaction. Funds withdrawn to Dwolla may then, in turn, be withdrawn with bank funds deposited as an ACH transaction.

====EU====

You may withdraw any amount as a direct deposit to your bank. There is a 2% fee on these withdrawals. Contact the exchange by e-mail for this service.

====Australia====

A per-withdrawal fee (2,000 JPY) is subtracted and the remaining amount is sent via international wire in the chosen currency. If not AUD then an exchange fee of 2.5% will be charged.

===International Wire===

To any IBAN, SWIFT/BIC and ABA routable bank<ref>[http://www.facebook.com/MtGox/posts/343372689080478 Mt.Gox now offers international wire transfer to all US Banks]</ref>. Fee applies.

==Transfers to Other Customers==

Mt. Gox funds, either USD or BTC, may be sent to another Mt. Gox customer using a redeemable Mt. Gox code (voucher).

==Customer Service==

The preferred method for obtaining service is to place a request through the exchange's [https://mtgox.zendesk.com help desk]. Another method is to send e-mail with the request.

==Wallet/Banking==

An account at this exchange can be considered to be an [[eWallet]]. This service also offers [[:Category:ECommerce|eCommerce]] merchant [https://mtgox.com/merch/about payment services].

==Security Center==

The Security Center allows an account to be secured through the use of one or more One Time Password (OTP) solutions such as what YubiKey and Google Authenticator offer. Features can be protected where the OTP must be provided for each action and are configured independently.

For example, a typical configuration is to set OTP as being required for both withdrawals and security center changes but not for login. With that configuration, the worst damage that can happen from a compromised account or session would be that bitcoins would be bought or sold (though they could also be bought and sold over and over until funds are depleted).

* Login - The OTP must be provided for each login.
* Withdraw - The OTP must be provided for each withdrawal request.
* Security - The OTP must be provided during each configuration change to be performed.

==AML==

Varying degrees of verification will allow for greater per-day and per-month total amounts to be withdrawn<ref>[http://support.mtgox.com/entries/20919111-aml-account-statuses AML Account Statuses]</ref>.

===Unverified (Level 0)===

Designed for basic users, consumers and Bitcoin enthusiasts where 10,000 USD (monthly) is enough for most needs.

===Verified (Level 1)===

The "verified" status is designed for active traders and/or small companies.

===Trusted (Level 2)===

The “trusted” status is designed for day traders, professionals, and companies.

==API==

Mt Gox offers an [[MtGox/API|API]] which can be used to automate operations.

==Data Services==

===Web===
* Bitstock live watcher for trades, depth, history [http://bitstock.info bitstock.info] (Websockets browser required)
* [[Bitcoin Charts]]
* Clark Moody's [[Real Time Bitcoin Market Data]] including Ticker, Order Book and Time Sales (Websockets browser support required)
* [[MtGox Live]] (Websockets browser support required)
* [[Bitcoin Arbitrage Opportunities]] (Websockets browser support required)
* [[Bitcoin Prices]] market rates in multiple currencies

===Windows===
* [[Sierra Chart MtGox Bridge]] trading and charting tool.
* [[ToyTrader]] command line trading tool

===Mac OS X===
* [[BitTicker]] for Mac OS X
* [http://sneak.datavibe.net/20110613/mtgoxwatcher MtGox Watcher] for Mac OS X

===Mobile===
* [[BitcoinX]] mobile app with bid, ask and 24 hour history. For Android
* [[MtGox Live]] Bitcoin Trader with buy, sell, send, chart and depth for Android and iOS

=== firefox addon ===
* [https://github.com/joric/mtgox-ticker] firefox ticker addon

===Linux===
* [http://www.goxsh.info goxsh] command line ticker / depth chart
* [https://github.com/3M3RY/tulpenmanie tulpenmanie] graphical trading platform

==E-Commerce==

Online sellers can accept bitcoins for payment using the Mt. Gox's E-commerce Solution, which is an interface to the exchange's [[MtGox/API/HTTP/v1#Merchant_System|Merchant System API]].

==History==
The exchange went online on July 18, 2010.<ref>[http://www.bitcoin.org/smf/index.php?topic=444.0 MtGox announcement on forum]</ref>

On October 10, 2010 the exchange switched from [[PayPal]] to Liberty Reserve as the main funding option as a result of this attack. Former PayPal customers still had the possibility to withdraw their USD using alternative methods.

On March 6th, 2011 ownership of the exchange changed hands<ref>[http://www.bitcoin.org/smf/index.php?topic=4187.0 Mtgox is changing owners]</ref>. Tibanne publishes their [http://legal.tibanne.com/docs/20110801_company_certificate.pdf company certificate] from the Japanese government.

On June 19, 2011 the service experienced a significant security breach<ref>[https://support.mtgox.com/entries/20224998-huge-bitcoin-sell-off-due-to-a-compromised-account-rollback Huge Bitcoin sell off due to a compromised account - rollback]</ref>. The incident caused a selloff down to BTC/USD of $0.01 due to fraudulent trading. The site was disabled and all trading following the point that fraudulent trading began was rolled back. Complicating this breach was the release of a list of the exchange's accounts including username, email address and a password hash, which forced the exchange to implement an account recovery method for customers to regain control of their accounts.

In July, 2011 it was observed that the exchange no longer allows new registrations to occur without having a valid e-mail address.

On July 19, 2011 a press release announced that MtGox had acquired [[MtGox Live]].<ref>[https://mtgox.com/press_release_20110719.html World's Leading Bitcoin Exchange, Mt.Gox, acquires MtGoxLive.com]</ref>

Announced on March 6, 2012 was the Merchant Solution and API<ref>[https://mtgox.com/press_release_20120306.html Mt.Gox launches the definitive bitcoin checkout solution]</ref>

==See Also==

* [[Buying bitcoins]]
* [[Selling bitcoins]]
* [[MtGox/API|API]]

==External Links==

* [https://mtgox.com MT. Gox exchange] website
* [https://mtgox.com/merch/about Mt. Gox Merchant Services]
* [https://mtgox.zendesk.com Customer Service Help Desk]

==References==
<references/>

[[Category:Exchanges]]
[[Category:eWallets]]
[[Category:Shopping Cart Interfaces]]
[[ru:MtGox]]

Buying bitcoins

2012-11-14T02:55:08Z

Jepo: /* Fixed Rate Exchanges & Others */ column too wide

There are various methods available for buying bitcoins. See [[Buying Bitcoins (the noob version)|here for a Noob-friendly version]] of this page.

Warning: Please be careful with your money. When sending money to an exchange or seller you are trusting that the operator will not abscond with your funds and that the operator maintains secure systems that protect against theft -- internal or external. It is recommended that you obtain the real-world identity of the operator and ensure that sufficient recourse is available. Exchanging or storing significant amounts of funds with exchanges is not recommended.

==Major Exchanges==

The least expensive methods for buying bitcoins involve transferring funds using a bank wire, ACH, bank transfer (ACH, EUR / SEPA).

Exchanges are listed in alphabetical order.

{| class="wikitable"
|-
| Exchange || Adding Funds || Withdrawing Funds || [[eWallet]] || Notes
|-
| [[Bitcoin-24]] || BTC USD ([[MtGox]] redeemable code) EUR ([[MtGox]] redeemable code) USD (VouchX redeemable code) EUR (VouchX redeemable code) EUR (BTC24 redeemable code) USD (Credit card through LiqPay) EUR (Sofortuberweisung) || BTC EUR (SEPA bank transfer) EUR (VouchX redeemable code) USD (VouchX redeemable code) EUR (BTC24 redeemable code) USD (BTC24 redeemable code USD ([[Skrill]]/Moneybookers) || {{Table Value Yes}} ||
|-
| [[Bitcoin-Central]] || BTC GBP (Bank transfer) EUR (SEPA) Liberty Reserve USD Liberty Reserve EUR International wire (any currency) || BTC GBP (Bank transfer) EUR (SEPA) Liberty Reserve USD Liberty Reserve EUR || {{Table Value Yes}} || [https://github.com/davout/bitcoin-central Open-source], community reviewed platform Available in French and English languages
|-
| [[Bitfloor]] || BTC USD (Cash deposit at Chase, Wells Fargo) USD (bank wire transfer) USD (ING Person2Person) || BTC USD (ACH, direct deposit) || {{Table Value Yes}} ||
|-
| [[BitMe]] || BTC USD (Cash deposits at Chase) USD (Wire Transfer - US) USD (Wire Transfer - International) USD (AurumXchange VouchX) || BTC USD (AurumXchange VouchX) USD (ACH / Direct Deposit) USD (Wire Transfer - US) || {{ Table Value Yes }} || <ul><li>US-based</li><li>Liquidity rebates</li><li>[https://github.com/bitme BitMe's GitHub]</li><li>[http://bitme.github.com/rest/ REST API]</li></ul>
|-
| [[bitNZ]] || BTC NZD (Cash depost as Westbank) || BTC NZD (Domestic bank transfer) || {{Table Value Yes}} ||
|-
| [[Bitstamp]] || BTC BTC (Redeemable code) EUR (SEPA transfer) USD (Intl wire) USD (Redeemable code) CHF || BTC BTC (Redeemable code) EUR (SEPA transfer) USD (Intl wire) USD (Redeemable code) CHF || {{Table Value Yes}} || EUR and CHF deposits converted to/from USD for trading
|-
| [[BTC-E]] || BTC BTC (BTC-e redeemable code) USD (Cash deposit at Post of Russia) USD (Cash deposit at banks including Privatbank, Savings Bank of Russia (Sberbank), RU/UA Terminals, & more) USD ([[Liberty Reserve]]) USD (Interkassa) USD (WebMoney - WMZ) USD (Yandex) USD (LiqPay) USD (Perfect Money) USD (QIWI) USD (OKPay) USD (RBK Money) USD (Ditial currencies including НСМЭП (NSMEP), Единый Кошелек (Unified Purse), TeleMoney, & more) USD (BTC-e Redeemable Code, available via BitInstant and AurumXChange) USD (International bank wire) RUB (QIWI) RUB (LiqPay) RUB (WebMoney-WMR) RUB (BTC-e Redeemable code) RUB (Bank transfer) || BTC BTC (BTC-e redeemble code) USD (Liberty Reserve) USD (Webmoney - WMZ) USD (Perfect Money) USD (LiqPay) USD (QIWI) USD (PayPal) USD (OKPay) USD (Payza/AlertPay) USD (Privat, Privat UAH) USD (Cash deposit into Savings Bank/Sberbank, Telebank, Alfa Bank) USD (BTC-e Redeemable Code) USD (International Wire Transfer) RUB (Cash delivery, possible in Moscow) RUB (QIWI) RUB (LiqPay) RUB (WebMoney WMR) RUB (Яндекс.Деньги Yandex) RUB (RBK Money) Cash deposit (into account at Сбербанка России!/Savings Bank/Sberbank, Телебанк (Telebank), and АльфаБанк (Alfa Bank) RUB (Transfer to credit card VISA & MasterCard) RUB (BTC-e Redeemable code) RUB (Bank transfer) || {{Table Value Yes}} || Language: English, Russian. Interkassa can be funded from Webmoney and many other methods. BitInstant Can be funding option includes QIWI, Cyberplat.
|-
| [[Camp BX]] (CBX) || BTC USD ([[Dwolla]]) USD (Personal Check) USD (USPS Postal money order, Canada Post money order) || BTC USD ([[Dwolla]]) USD (ACH Direct Deposit) USD (USPS Postal Money Order) USD (Domestic bank wire) USD (International bank wire) || {{Table Value Yes}} || <ul> <li> Security certification from McAfee</li><li> Advanced trading options with AON/FOK/Market</li> <li>STOPLOSS and Short-Selling in Pipeline</li><li> Trading API available</li><li> Wallet API available </li><li> CBX Instant Bitcoin Transfers Feature </li><li> Stoploss / Custom Order Expiry Date/Time </li><li> SMS (Text Message) Notifications </li> <li> Two-Factor Authentication </li> <li> Based in USA - Atlanta </li> </ul>
|-
| [[CryptoXchange]] || BTC USD (Redeemable code from Mt. Gox) USD (Redeemable code from CryptoXChange) USD (BitInstant) USD (AurumXChange) AUD (Cash deposit at Westpack) NMC || BTC USD (Redeemable code from Mt. Gox) USD (Redeemable code from CryptoXChange) USD (International bank wire) NMC || {{Table Value Yes}} || <ul> <li> Buy Gold,Silver,Palladium and Casascius physical bitcoins plus other items in the store.</li> <li> Affiliate program.</li> <li> Mining Pool integration program.</li> <li> Bitcoin, Namecoin and Litecoin </li> <li>Multiple Authentication Levels</li> <li> API </li> <li> Free Yubikey's to High Volume Traders </li> <li> An Australian Owned and Operated Registered Company.</li> <li>
Inquiries: contact@cryptoxchanger.com or Phone: +61280050602 </li> </ul>
|-
| [[Intersango]] || BTC EUR (SEPA bank wire) PLN (Bank Wire) || BTC EUR (SEPA bank wire) PLN (Bank Wire) || {{Table Value Yes}} || Operated by the [https://bitcoinconsultancy.com/ BitcoinConsultancy] [https://intersango.com Intersango] is a completely custom trading platform built from the ground up with security, scalability and extensibility in mind. [https://bitcointalk.org/index.php?topic=43745.0 More Information] Boasts an [https://bitcoinconsultancy.com/wiki/index.php/Intersango/API ever expanding API]. Started out as [[Britcoin]].
|-
| [[Kapiton.se]] || BTC SEK (Bankgiro Bank Transfer) || BTC SEK (Bankgiro Bank Transfer) || {{Table Value Yes}} ||
|-
| [[Mercado Bitcoin]] || BTC BRL (Bank transfer) BRL (Bank transfer - MoIP) Liberty Reserve USD || BTC BRL (Bank transfer - MoIP) || {{Table Value Yes}} || Language: Portugese
|-
| [[MtGox]] || BTC BTC (Redeemable code) USD ([[Dwolla]]) USD (International bank wire) USD (Wire to [[AurumXChange Company|AurumXChange]]) USD ([[OKPay]]) AUD (Bank wire) GBP (Bank wire) GBP (Cash deposit, Barclays) USD (Redeemable code) Liberty Reserve USD (via AurumXChange) || BTC BTC (Redeemable code) USD ([[Dwolla]]) USD (Wire via [[AurumXChange Company|AurumXChange]]) AUD (Bank wire) USD (Redeemable code) Liberty Reserve USD (via AurumXChange) || {{Table Value Yes}} || Oldest running exchange. Higest daily volume. Respecting AML laws, Restrictions and limits on withdrawals.
|-
| [[Rock Currency Exchange]] || BTC EUR (SEPA transfer) SLL (Second Life) USD (Dwolla) || BTC EUR (SEPA transfer) SLL (Second Life) USD (Dwolla) || {{Table Value Yes}} ||
|-
| [[VirtEx]] || BTC CAD (cash deposit at Royal Bank, Bank of Montreal or ScotiaBank) CAD (Online bill payment) CAD (Wire transfer) || BTC CAD (direct deposit) CAD (Canada Xpress Post Bank Draft send by mail) CAD Payza (formerly AlertPay) || {{Table Value Yes}} ||
|-
| [[VirWoX]] || BTC SLL (Second Life) ACD (Avination) OMC (OpenSim) USD,EUR,GBP,CHF ([[PayPal]]) USD,EUR,GBP (Credit & Debit cards via [[Skrill]]/Moneybookers) USD,EUR,GBP ([[NETELLER]]) EUR (DIRECTebanking / Sofortuberweisung) USD,EUR,GBP,CHF ([[paysafecard]]) EUR (SEPA bank transfer) USD ([[UKash]] vouchers) || BTC SLL (Second Life) ACD (Avination) OMC (OpenSim) USD,EUR,GBP,CHF ([[PayPal]]) USD,EUR,GBP ([[Skrill]]/Moneybookers) USD,EUR,GBP ([[NETELLER]]) EUR (SEPA bank transfer) || {{Table Value Yes}} || Trading through Second Life Linden Dollars. Variable limits on PayPal and Credit Card deposits.
|}

==Fixed Rate Exchanges & Others==

For smaller amounts, the options are limited due to bank transfer fees, conversion fees and transaction size restrictions. Options include:

{| class="wikitable"
|-
| Service || Type || Payment Method || Notes
|-
| [https://www.bitcopia.com Bitcopia] ([[Bitcopia.com|info]]) || Fixed Rate || USD (Cash deposit) || Anonymous transactions. Instant quotes based on live Mt Gox prices. Cash deposit at any Wells Fargo in the US.
|-
| [http://www.coinmarket.co.nz/buy The Daktory CoinMarket] || Fixed Rate || NZD (NZ Bank deposit/Cash) || Cash deposit or bank transfer to domestic New Zealand bank. Cash payment to brokerage. Guest checkout available.
|-
| [[Bit Innovate]] || Fixed Rate || AUD (Cash deposit) || Australian Dollar cash deposit at any Commonwealth Bank.
|-
| [[BitInstant]] || Market Rate || USD (Cash deposit at banks, 7-11, Walmart, CVS, Moneygram locations) USD (Dwolla) BRL (Cash deposit at Banco Rendimento or through Boleto) RUB (Cash deposit through Qiwi or Cyberplat) || Deposit cash at 700,000 locations around the world and have your Bitcoins within 30 minutes. Absolute fastest and easiest way to buy Bitcoins.
|-
| [[Coinapult]] || Fixed rate || Use [[BitInstant]] to use cash to purchase bitcoins sent to e-mail or SMS. Choose "Bitcoin to e-mail" service and enter either e-mail or SMS. ||
|-
| [[Coinbase]] || Fixed rate || Buy bitcoins using a bank transfer (U.S.). || Instant verification available for new accounts.
|-
| [[Bitcoin Nordic]] || Fixed Rate
|
*EUR/DKK (SEPA and wire transfer)
*USD, EUR, GBP, DKK, SEK, NOK (Cash or check in the mail)
*AED, DZD, EGP, IQD, ILS, JOD, KWD, LGP, LYD, MRO, MYR, NGN, OMR, PKR, QAR, SAR, TRL, TZS, TND, YER ([[CashU]] card)
*MXN, EYU, BOB, BRL, COP, SYP, MAD, GHC, ZAR, CNY, CAD, and more ([[UKash]] voucher)
| For UKash, redeemed through CashU account.
|-
| [https://blockchain.info/wallet/sms-phone-deposits Blockchain.info] ([[BlockChain.info|info]]) || Fixed Rate || USD, BRL, AUD, CAD, JPY, EUR, CHF, GBP, PLN, CZK, RON, RUB, SEK, NOK, DKK || Purchased through [[BitInstant]] (U.S., Brazil, and Russia), Barclay's Pingit (GBP), or SMS or premium phone call from a mobile. Or Bank Deposit for UK Users.
|-
| [[Omnicoins]] || Fixed Rate || AUD (Cash deposit) || Deposit cash at any Commonwealth, NAB, or Westpac branch.
|-
| [[Spend Bitcoins]] || Fixed Rate || AUD (Cash deposit) || AUD cash deposit at NAB, Commonwealth Bank, Westpac and ANZ.
|-
| [https://bitcoinmylife.com/jml/buy-bitcoins BitcoinMyLife] ([[BitcoinMyLife|info]]) || Fixed Rate || EUR (SEPA bank transfer) || Simple and Safe. Pay first transaction fee with Twitter or Facebook post.
|-
| [[bitcoin.de]] || Market || EUR (bank wire) EUR (SEPA bank transfer) EUR (Liberty Reserve) EUR ([[Skrill]]/Moneybookers) || Varies (person to person) 0.01 free Bitcoins for every new user eWallet Affiliate program Language: German, Englisch News
|-
| [[Blizzcoin]] || Fixed Rate || EUR (SEPA bank transfer) || Buy Bitcoins within minutes. Instant exchange. No registration.
|-
| [[BitMarket.eu]] || Market || EUR (Euro) GBP (British Sterling Pound) USD (U.S. Dollar) PLN (Polish złoty) AUD (Australian Dollar) CAD (Canadian Dollar) ZAR (South African Rand) ILS (Israeli Shekel) CHF (Swiss Franc) RUB (Russian Ruble) || Varies (person to person)
|-
| [[Bitcoiny.cz]] || Market || CZK || Varies (person to person)
|-
| [[Mr Bitcoins|Mr. Bitcoins]]|| Fixed Rate || AUD (Cash deposit - Westpack and Commonwealth Bank) USD (Major banks, 7-11, Walmart, CVS) RUB (Qiwi and Cyberplat through BitInstant) BRL (Boleto through BitInstant) INR (Cash deposit - HDFC Bank)|| 100% Anonymous Cash Deposits
|-
| [[BTCX.se]] || Fixed Rate || SEK || Transfer to and banks in Sweden.
|-
| [[BTC China]] || Fixed Rate || USD (Liberty Reserve) || Converted to CNY for trading.
|-
| [[BitMarket.co]] || Market || COP (Colombian Peso) || Varies (person to person)
|-
| [[bitcoin-otc|#bitcoin-otc]] || [http://bitcoin-otc.com/vieworderbook.php Order Book] || Varies (person to person) || IRC trading marketplace will usually have people willing to deal for small and larger amounts using various payment methods, including [[PayPal]], [[Dwolla]], [[Linden Dollars]], etc.
|-
| [[Canadian Bitcoins]] || Fixed Rate || CAD (Cash - XpressPost or Dropoff) USD (Cash - Courier: UPS, FedEx, etc.) || For dropoff, office in Ottawa.
|-
| [https://dgtmkt.com Dgtmkt] ([[Dgtmkt|info]]) || Fixed Rate || Malaysian Ringgit (MYR) Online bank transfers (Maybank2U, CIMB, MEPS, etc) E-vouchers (Web Cash, Mobile Money) || Bitcoin merchant for Malaysians, dealing in Malaysian Ringgit. Fully automated immediate transfers. https://dgtmkt.com
|-
| [[Lilion Transfer]] || Fixed Rate || Bank Transfer: USD, AUD, CAD, JPY, EUR, CHF, GBP, PLN, CZK, RON, BGN, HRK, RUB, SEK, NOK, DKK, LTL, LVL Liberty Reserve Perfect Money Monetto OK Pay Cosmic Pay Pecunix C-Gold E-Pay Payments PayPal|| 122 accounts worldwide. Support in 30 languages
|-
| [[Nanaimo Gold]] || Fixed Rate || USD (Liberty Reserve) Western Union money transfer Moneygram money transfer Cash in the mail || LR <--> Bitcoin exchange is automated For cash in the mail send USD, EUR, CAD, or GBP. Canada mailing address.
|-
| [[Bitcoin Argentina]] || Fixed Rate || Cash: ARS, BRL, USD Bank transfer: ARS || No exchange fees!
|-
| [[Bitcoin.com.es]] || Fixed Rate || EUR (bank deposit) || Bank transfer or cash deposits at OpenBank in Spain.
|-
| [[Bahtcoin]] || Fixed Rate || Cash, Webmoney Liberty Reserve USD || Will cash out to Thai mobile and gaming prepaid cards as well.
|-
| [[Bitcoin Brasil]] || Fixed Rate || BRL (Brazilian Real) USD || Cash exchange
|-
| [[BitPiggy]] || Fixed Rate || AUD (Australian Dollar)|| Payment via bank transfer.
|-
| [[bitcoin.local]] || Directory || Varies (person to person) ||
|-
| [[bcchanger.com]] || Directory || Enables person to person purchases and sales via PayPal, [[Skrill]]/Moneybookers and other e-currency platforms ||
|-
| [[anonXchange]] || Fixed Rate || EUR GBP || Liberty Reserve, Paysafecard and Ukash to Bitcoin
|-
| [[Bitcoil]] || Fixed Rate || ILS (bank transfer) ||
|-
|[[btcnow]] || Market || USD (OKPay, Dwolla) || bitcoins transferred instantly
|-
| [http://localbitcoins.com LocalBitcoins.com] || Directory || Varies (person to person) Physical cash locally || Find your local bitcoin dealer! With dynamic pricing with equations.
|-
| [[WM-Center]] || Fixed rate || BTC USD (International bank wire, Western Unon, Moneygram, Xoom etc, cash) EUR (IBAN bank wire) RUB (bank wire, WU, Anelik and etc, cash) AUD (Bank wire) Liberty Reserve USD/EUR, Perfect Money USD/EUR, Pecunix, Paxum, c-gold, Hoopay, GDP || 24/7/365 support in English, Spanish and Russian.
|-
| [[ECurrencyZone]] || Fixed Rate || BTC INR (Cash deposit of Indian rupee) BDT (Cash deposit of Bangladeshi taka) NPR (Cash deposit of Nepalese rupee) MYR (Cash deposit of Malaysian ringitt) SGD (Cash deposit of Singaporean dollar) SGD (Net/Bank transfer) USD (Western Union, Moneygram, Citibank global funds transfer, OKPay) USD (Liberty Reserve, Mt. Gox redeemable code) || Bank transfer considered at all locations with prior approval.
|-
| [[BitCoinVend]] || Market || BTC USD (PayPal) || bitcoinvend@gmail.com, market variable with commission, quote based, verified paypal account with anti scammer verification
|-
| [[Bitcoins In Berlin]] || Fixed Rate || EUR (Cash in-the mail) EUR (Cash in-person trade) EUR (SEPA bank transfer) EUR (Mt. Gox [[redeemable code]]) EUR (Western Union) || Cash in-the-mail is to a Berlin P.O. box. In-person trade is in Berlin.
|-
| [[Mang Sweeney]] || Fixed Rate || PHP (Cash) PHP (Cash deposit at bank) || Languages: English, Pinoy. PHP [https://localbitcoins.com/accounts/profile/mangsweeney cash trade method] in metro Manilla, Philappines.
|-
| [http://bitcoinvender.yolasite.com/ Bitcoin Vender] || Fixed Rate|| USD (Credit Card) USD (Debit Card) || Buy bitcoins with your credit or debit card
|-
| [[mercaBit.eu]] || Fixed Rate|| EUR (ukash) EUR (paysafecard) EUR (neosurf) EUR (halcash) EUR (teleingreso) || Buy bitcoins with ukash and more
|-
| [http://buyBTC.cz buyBTC.cz] ([[buyBTC.cz|info]]) || Fixed Rate|| CZK (Domestic bank transfer) EUR (Bank transfer) || Buy bitcoins from the Czech Republic.
|-
| [http://InstaWire.com InstaWire.com] ([[InstaWire|info]]) || Fixed Rate|| EUR (SEPA bank transfer) || No sign-up, just enter the amount and a Bitcoin address.
|-
| [http://bitonic.nl Bitonic.nl] || Fixed Rate|| EUR (iDeal) || Buy bitcoins instantly from the Netherlands.
|-
| [http://swissbitcoins.ch swissbitcoins.ch] || Fixed Rate|| CHF (Swiss Bank Transfer) || Buy Bitcoins in Switzerland. No registration required. Enter Bitcoin address, wire money and get your bitcoins within 24 hours.
|-
| [http://www.dragons.tl Dragon's Tale] ([[Dragon's Tale|info]]) || Other || Credit card (except in the U.S.) || Purchase bitcoins through this MMO casino with credit card, withdraw bitcoins (though a fee applies if withdrawn and no casino play.)
|}

==Direct / Bulk Buying==

{| class="wikitable"
|-
| Service || Type || Payment Method || Notes
|-
| [http://bitcointalk.org/index.php?topic=87094.0 Bitcoins Direct] || Direct purchases, $500 to $5,000 USD. || USD (Cash deposit at B of A, Wells Fargo or PNC Bank USD (Bank wire, domestic or international) USD (Cashier check, by mail) USD (Liberty Reserve) || BTC || Inventory varies based on market conditions.
|-
| [http://bitcointalk.org/index.php?topic=89757.msg996082#msg996082 BitPay] ([[BitPay|info]]) || Direct purchases, $10,000 USD and higher || USD (Bank wire, domestic or international) || BTC || Contact for other payment methods.
|}

==Other Financial Services==

{| class="wikitable"
|-
| Service || Type || Payment || Settled || Notes
|-
| [[MPEx]] || Buy / Sell / Exercise CALLs / PUTs, American style. 52 strikes offered (by .5), current month + 2. No shorting available yet.|| BTC || BTC || Transactions encoded via amt. Must use non-rounding client (0.3.24 or later)
|-
| [https://vircurex.com Vircurex] || Buy / Sell Options Loan / Borrow || BTC, NMC, LTC, DVC, GG, I0C, IXC, SC || BTC, NMC, LTC, DVC, GG, I0C, IXC, SC ||
|}

==Physical Bitcoins==

Physical Bitcoins are bearer tokens that have an embedded redeemable digital bitcoin value if torn open. While they are somewhat expensive if bought purely for the digital bitcoins, they are relatively easy to get, because they can be purchased with PayPal or credit card - payment methods not typically not accepted for pure digital bitcoin purchases.

{| class="wikitable"
|-
| Service || Type || Payment || Notes
|-
| [http://www.memorydealers.com Memory Dealers] || Casascius Physical Bitcoins || USD (PayPal/Credit Card) ||
|-
| [https://www.casascius.com Casascius.com] || Casascius Physical Bitcoins || BTC ||
|-
| [https://www.giftcoin.net/card Bitcoin Gift Card] || Bitcioin Gift Card Physical Bitcoin Issued By GiftCoin || BTC ||
|-
| [http://www.bitbills.com Bitbills] || Bitbills cards || BTC || Not taking orders as of Nov 2011.
|}

==See Also==

* [[:Category:Digital_currencies|Digital Currencies]]
* [[Selling bitcoins]]
* [[Secure Trading]]
* [[:Category:Local|Local]] exchanges

[[Category:Exchanges]]
[[Category:Introduction]]
[[zh-cn:购买bitcoins]]
[[ru:Приобретение биткойнов]]

Help:FAQ

2012-10-25T15:46:51Z

Jepo: /* What do I call the various denominations of Bitcoins? */

Here you will find answers to the most commonly asked questions.

== General ==
=== What are bitcoins? ===
Bitcoins are the unit of currency of the Bitcoin system. A commonly used shorthand for this is “BTC” to refer to a price or amount (eg: “100 BTC”).
There are such things as [[physical bitcoins]], but ultimately, a bitcoin is just a number associated with a [[Address|Bitcoin Address]]. A physical bitcoin is simply an object, such as a coin, with the number carefully embedded inside. See also an [[Introduction|easy intro]] to bitcoin.

=== How can I get bitcoins? ===

There are a variety of ways to acquire bitcoins:

* Accept bitcoins as payment for goods or services.
* There are several services where you can [[buying bitcoins|trade them]] for traditional currency.
* Find someone to trade cash for bitcoins in-person through a [https://en.bitcoin.it/wiki/Category:Directories local directory].
* Participate in a [[Pooled mining|mining pool]].
* If you have a lot of mining hardware, you can solo mine and attempt to create a new [[block]] (currently yields 50 bitcoins).

===Does Bitcoin guarantee an influx of free money?===

Since Bitcoin is a new technology, what it is and how it works may be initially unclear. Bitcoin is sometimes presented as being one of three things:
<ol style="list-style-type: upper-alpha;">
<li>Some sort of online 'get-rich-quick' scam.</li>
<li>A loophole in the market economy, the installation of which guarantees a steady influx of cash.</li>
<li>A sure investment that will almost certainly yield a profit.</li>
</ol>
In fact, none of the above are true. Let's look at them independently.

;Is Bitcoin a 'get-rich-quick' scheme?
:If you've spent much time on the Internet, you've probably seen ads for many 'get-rich-quick' schemes. These ads usually promise huge profits for a small amounts of easy work. Such schemes are usually pyramid/matrix-style schemes that make money from their own employees and offer nothing of any real value. Most convince one to buy packages that will make them earn hundreds a day, which in fact have the buyer distribute more such ads, and make minute profits.

:Bitcoin is in no way similar to these schemes. Bitcoin doesn't promise windfall profits. There is no way for the developers to make money from your involvement or to take money from you. That bitcoins are nearly impossible to acquire without the owner's consent represents one of its greatest strengths. Bitcoin is an experimental, virtual currency that may succeed or may fail. None of its developers expect to get rich off of it.

:A more detailed answer to this question can be found [http://bitcointalk.org/?topic=7815.0 here].

;Will I make money by installing the client?
:Most people who use Bitcoin don't earn anything by doing so, and the default client has no built-in way to earn Bitcoins. A small minority of people with dedicated, high-performance hardware do earn some Bitcoins by "''mining''" (generating new bitcoins, see [[#What is mining?|What is mining?]]) with special software, but joining Bitcoin shouldn't be construed as being the road to riches. Most Bitcoin users get involved because they find the project conceptually interesting and don't earn anything by doing so. This is also why you won't find much speculation about the political or economic repercussions of Bitcoin anywhere on this site: Bitcoin developers owe their dedication to the project's intellectual yieldings more than to those of a monetary nature. Bitcoin is still taking its first baby steps; it may go on to do great things but right now it only has something to offer those chasing conceptually interesting projects or bleeding edge technology.

;As an investment, is Bitcoin a sure thing?
:Bitcoin is a new and interesting electronic currency, the value of which is not backed by any single government or organization. Like other currencies, it is worth something partly because people are willing to trade it for goods and services. Its exchange rate fluctuates continuously, and sometimes wildly. It lacks wide acceptance and is vulnerable to manipulation by parties with modest funding. Security incidents such as website and account compromise may trigger major sell-offs. Other fluctuations can build into positive feedback loops cause much larger exchange rate fluctuations. Anyone who puts money into Bitcoin should take measures to reduce their risk and consider it as a high-risk currency. Later, as Bitcoin becomes better known and more widely accepted, it should stabilize, but for the time being it is unpredictable. Any investment in Bitcoin should be done carefully and with a clear plan to manage risk.

=== Can I buy bitcoins with Paypal? ===

It is possible to buy [[physical bitcoins]] with PayPal but it is otherwise difficult and/or expensive to do so, because of significant risk to the seller.

While it is possible to find an individual who wishes to sell Bitcoin to you via Paypal, (perhaps via [http://www.bitcoin-otc.com/ #bitcoin-otc] ) most exchanges do not allow funding through PayPal. This is due to repeated cases where someone pays for bitcoins with Paypal receives their bitcoins, and then fraudulently complains to Paypal that they never received their purchase. PayPal often sides with the fraudulent buyer in this case which means any seller would need to cover that risk with higher fees or refuse to accept PayPal altogether.

Buying Bitcoins from individuals with this method is still possible, but requires the seller to have some trust that the buyer will not file a claim with PayPal to reverse the payment.

=== Where can I find a forum to discuss Bitcoin? ===

Please visit the [[Bitcoin:Community_portal#Bitcoin_Community_Forums_on_various_platforms|Community Portal]] for links to Bitcoin-related forums.

=== How are new bitcoins created? ===

[[File:total_bitcoins_over_time_graph.png|thumb|Number of bitcoins over time, assuming a perfect 10-minute interval.]]
New bitcoins are generated by the network through the process of "[[#What is mining?|''mining'']]". In a process that is similar to a continuous lottery, mining nodes on the network are awarded bitcoins each time they find the solution to a certain mathematical problem (and thereby create a new [[block]]). Creating a block is a [[proof of work]] with a difficulty that varies with the overall strength of the network. The reward for solving a block is [[Controlled Currency Supply|automatically adjusted]] so that in roughly the first four years of operation of the Bitcoin network, {{formatnum:10500000}} BTC will be created. This amount is halved each four years, so it will be {{formatnum:5250000}} over years 4-8, {{formatnum:2625000}} over years 8-12, and so on. Thus the total number of bitcoins in existence will not exceed {{formatnum:21000000}}. See [[Controlled Currency Supply]].

Blocks are [[Mining|mined]] every 10 minutes, on average and for the first four years ({{formatnum:210000}} blocks) each block includes 50 new bitcoins. As the amount of processing power directed at mining changes, the difficulty of creating new bitcoins changes. This difficulty factor is calculated every 2016 blocks and is based upon the time taken to generate the previous 2016 blocks. See [[Mining]].

=== What's the current total number of bitcoins in existence? ===

[http://blockexplorer.com/q/totalbc Current count]. Also see [https://blockchain.info/charts/total-bitcoins Total bitcoins in circulation chart]

The number of blocks times the coin value of a block is the number of coins in existence. The coin value of a block is 50 BTC for each of the first {{formatnum:210000}} blocks, 25 BTC for the next {{formatnum:210000}} blocks, then 12.5 BTC, 6.25 BTC and so on.

=== How divisible are bitcoins? ===

A bitcoin can be divided down to 8 decimal places. Therefore, 0.00000001 BTC is the smallest amount that can be handled in a transaction. If necessary, the protocol and related software can be modified to handle even smaller amounts.

=== What do I call the various denominations of bitcoins? ===

There is a lot of discussion about the naming of these fractions of bitcoins. The leading candidates are:

* 1 BTC = 1 bitcoin
* 0.01 BTC = 1 cBTC = 1 centibitcoin (also referred to as bitcent)
* 0.001 BTC = 1 mBTC = 1 millibitcoin (also referred to as mbit (pronounced em-bit) or millibit or even bitmill)
* 0.000 001 BTC = 1 μBTC = 1 microbitcoin (also referred to as ubit (pronounced yu-bit) or microbit)

The above follows the accepted international SI prefixes for hundredths, thousandths, and millionths. There are many arguments against the special case of 0.01 BTC since it is unlikely to represent anything meaningful as the Bitcoin economy grows (it certainly won't be the equivalent of 0.01 USD, GBP or EUR). Equally, the inclusion of existing national currency denominations such as "cent", "nickel", "dime", "pence", "pound", "kopek" and so on are to be discouraged; this is a worldwide currency.

One exception is the "satoshi" which is smallest denomination currently possible

* 0.000 000 01 BTC = 1 satoshi (pronounced sa-toh-shee)
which is so named in honour of Satoshi Nakamoto, the pseudonym of the inventor of Bitcoin.

For an overview of all defined units of Bitcoin (including less common and niche units), see [[Units]].

Further discussion on this topic can be found on the forums here:

* [http://forum.bitcoin.org/index.php?topic=14438.msg195287#msg195287 We need names]
* [http://forum.bitcoin.org/index.php?topic=8282.0 What to call 0.001 BTC]

=== How does the halving work when the number gets really small? ===

Eventually the reward will go from 0.00000001 BTC to zero and no more bitcoins will be created.

The block reward calculation is done as a right bitwise shift of a 64-bit signed integer, which means it is divided by two and rounded down. The integer is equal to the value in BTC * 100,000,000 since internally in the reference client software, all Bitcoin balances and values are stored as unsigned integers.

With an initial block reward of 50 BTC, it will take many 4-year periods for the block reward to reach zero.

=== How long will it take to generate all the coins? ===

The last block that will generate coins will be block #6,929,999 which should be generated at or near the year 2140. The total number of coins in circulation will then remain static at 20,999,999.9769 BTC.

Even if the allowed precision is expanded from the current 8 decimals, the total BTC in circulation will always be slightly below 21 million (assuming everything else stays the same). For example, with 16 decimals of precision, the end total would be 20,999,999.999999999496 BTC.

=== If no more coins are going to be generated, will more blocks be created? ===

Absolutely! Even before the creation of coins ends, the use of [[transaction fee|transaction fees]] will likely make creating new blocks more valuable from the fees than the new coins being created. When coin generation ends, these fees will sustain the ability to use bitcoins and the Bitcoin network. There is no practical limit on the number of blocks that will be mined in the future.

=== But if no more coins are generated, what happens when Bitcoins are lost? Won't that be a problem? ===

Because of the law of supply and demand, when fewer bitcoins are available the ones that are left will be in higher demand, and therefore will have a higher value. So, as Bitcoins are lost, the remaining bitcoins will eventually increase in value to compensate. As the value of a bitcoin increases, the number of bitcoins required to purchase an item '''de'''creases. This is a [[Deflationary spiral|deflationary economic model]]. As the average transaction size reduces, transactions will probably be denominated in sub-units of a bitcoin such as millibitcoins ("Millies") or microbitcoins ("Mikes").

The Bitcoin protocol uses a base unit of one hundred-millionth of a Bitcoin ("a Satoshi"), but unused bits are available in the protocol fields that could be used to denote even smaller subdivisions.

=== If every transaction is broadcast via the network, does Bitcoin scale? ===
The Bitcoin protocol allows lightweight clients that can use Bitcoin without downloading the entire transaction history. As traffic grows and this becomes more critical, implementations of the concept will be developed. Full network nodes will at some point become a more specialized service.

With some modifications to the software, full Bitcoin nodes could easily keep up with both VISA and MasterCard combined, using only fairly modest hardware (a single high end server by todays standards). It is worth noting that the MasterCard network is structured somewhat like Bitcoin itself - as a peer to peer broadcast network.

Learn more about [[Scalability]].

==Economy==
=== Where does the value of Bitcoin stem from? What backs up Bitcoin? ===
Bitcoins have value because they are useful and because they are [[Controlled Currency Supply|scarce]]. As they are accepted by more merchants, their value will [http://en.wikipedia.org/wiki/Sticky_%28economics%29 stabilize]. See the [[Trade|list of Bitcoin-accepting sites]].

When we say that a currency is backed up by gold, we mean that there's a promise in place that you can exchange the currency for gold. Bitcoins, like dollars and euros, are not backed up by anything except the variety of merchants that accept them.

It's a common misconception that Bitcoins gain their value from the cost of electricity required to generate them. Cost doesn't equal value – hiring 1,000 men to shovel a big hole in the ground may be costly, but not valuable. Also, even though scarcity is a critical requirement for a useful currency, it alone doesn't make anything valuable. For example, your fingerprints are scarce, but that doesn't mean they have any exchange value.

=== Is Bitcoin a bubble? ===
Yes, in the same way as the euro and dollar are. They only have value in exchange and have no inherent value. If everyone suddenly stopped accepting your dollars, euros or bitcoins, the "bubble" would burst and their value would drop to zero. But that is unlikely to happen: even in Somalia, where the government collapsed 20 years ago, [http://en.wikipedia.org/wiki/Somali_shilling Somali shillings] are still accepted as payment.

=== Is Bitcoin a Ponzi scheme? ===
In a Ponzi Scheme, the founders persuade investors that they’ll profit. Bitcoin does not make such a guarantee. There is no central entity, just individuals building an economy.

A ponzi scheme is a zero sum game. Early adopters can only profit at the expense of late adopters. Bitcoin has possible win-win outcomes. Early adopters profit from the rise in value. Late adopters, and indeed, society as a whole, benefit from the usefulness of a stable, fast, inexpensive, and widely accepted p2p currency.

The fact that early adopters benefit more doesn't alone make anything a Ponzi scheme. All good investments in successful companies have this quality.

=== Doesn't Bitcoin unfairly benefit early adopters? ===
Early adopters have a large number of bitcoins now because they took a risk and invested resources in an unproven technology. By so doing, they have helped Bitcoin become what it is now and what it will be in the future (hopefully, a ubiquitous decentralized digital currency). It is only fair they will reap the benefits of their successful investment.

In any case, any bitcoin generated will probably change hands dozens of time as a medium of exchange, so the profit made from the initial distribution will be insignificant compared to the total commerce enabled by Bitcoin.

Since the pricing of Bitcoins has fallen greatly from its June 2011 peak, prices today are much more similar to those enjoyed by many early adopters. Those who are buying Bitcoins today likely believe that Bitcoin will grow significantly in the future. Setting aside the brief opportunity to have sold Bitcoins at the June 2011 peak enjoyed by few, the early-adopter window is arguably still open.

===Won't loss of wallets and the finite amount of Bitcoins create excessive deflation, destroying Bitcoin? ===
Worries about Bitcoin being destroyed by deflation are not entirely unfounded. Unlike most currencies, which experience inflation as their founding institutions create more and more units, Bitcoin will likely experience gradual deflation with the passage of time. Bitcoin is unique in that only a small amount of units will ever be produced (twenty-one million to be exact), this number has been known since the project's inception, and the units are created at a predicable rate.

Also, Bitcoin users are faced with a danger that doesn't threaten users of any other currency: if a Bitcoin user loses his wallet, his money is gone forever, unless he finds it again. And not just to him; it's gone completely out of circulation, rendered utterly inaccessible to anyone. As people will lose their wallets, the total number of Bitcoins will slowly decrease.

Therefore, Bitcoin seems to be faced with a unique problem. Whereas most currencies inflate over time, Bitcoin will mostly likely do the just the opposite. Time will see the irretrievable loss of an ever-increasing number of Bitcoins. An already small number will be permanently whittled down further and further. And as there become fewer and fewer Bitcoins, the laws of supply and demand suggest that their value will probably continually rise.

Thus Bitcoin is bound to once again stray into mysterious territory, because no one exactly knows what happens to a currency that grows continually more valuable. Economists generally agree that a low level of inflation is a good thing for a currency, but nobody is quite sure about what might happens to one that continually deflates. Although deflation could hardly be called a rare phenomenon, steady, constant deflation is unheard of. There may be a lot of speculation, no one has any hard data to back up their claims.

That being said, there is a mechanism in place to combat the obvious consequences. Extreme deflation would render most currencies highly impractical: if a single Canadian dollar could suddenly buy the holder a car, how would one go about buying bread or candy? Even pennies would fetch more than a person could carry. Bitcoin, however, offers a simple and stylish solution: infinite divisibility. Bitcoins can be divided up and trade into as small of pieces as one wants, so no matter how valuable Bitcoins become, one can trade them in practical quantities.

In fact, infinite divisibility should allow Bitcoins to function in cases of extreme wallet loss. Even if, in the far future, so many people have lost their wallets that only a single Bitcoin, or a fraction of one, remains, Bitcoin should continue to function just fine. No one can claim to be sure what is going to happen, but deflation may prove to present a smaller threat than many expect.

For more information, see the [[Deflationary spiral]] page.

=== What if someone bought up all the existing Bitcoins? ===
Bitcoin markets are competitive -- meaning the price of a bitcoin will rise or fall depending on supply and demand at certain price levels. Only a fraction of bitcoins issued to date are found on the exchange markets for sale. So even though technically a buyer with lots of money could buy all the bitcoins offered for sale, unless those holding the rest of the bitcoins offer them for sale as well, even the wealthiest, most determined buyer can't get at them.

Additionally, new currency continues to be issued daily and will continue to do so for decades though over time the rate at which they are issued declines to insignificant levels. Those who are mining aren't obligated to sell their bitcoins so not all bitcoins will make it to the markets even.

This situation doesn't suggest, however, that the markets aren't vulnerable to price manipulation. It doesn't take significant amounts of money to move the market price up or down and thus Bitcoin remains a volatile asset.

===What if someone creates a new block chain, or a new digital currency that renders Bitcoin obsolete?===

That the block chain cannot be easily forked represents one of the central security mechanisms of Bitcoin. Given the choice between two block chains, a Bitcoin miner always chooses the longer one - that is to say, the one with the more complex hash. Thusly, it ensures that each user can only spend their bitcoins once, and that no user gets ripped off.

As a consequence of the block chain structure, there may at any time be many different sub-branches, and the possibility always exists of a transaction being over-written by the longest branch, if it has been recorded in a shorter one. The older a transaction is though, the lower its chances of being over-written, and the higher of becoming permanent. Although the block chain prevents one from spending more Bitcoins than one has, it means that transactions can be accidentally nullified.

A new block chain would leave the network vulnerable to [[double-spending|double-spend]] attacks. However, the creation of a viable new chain presents considerable difficulty, and the possibility does not present much of a risk.

Bitcoin will always choose the longer Block Chain and determines the relative length of two branches by the complexities of their hashes. Since the hash of each new block is made from that of the block preceding it, to create a block with a more complex hash, one must be prepared to do more computation than has been done by the entire Bitcoin network from the fork point up to the newest of the blocks one is trying to supersede. Needless to say, such an undertaking would require a very large amount of processing power and since Bitcoin is continually growing and expanding, it will likely only require more with the passage of time.

A much more distinct and real threat to the Bitcoin use is the development of other, superior virtual currencies, which could supplant Bitcoin and render it obsolete and valueless.

A great deal of careful thought and ingenuity has gone into the development of Bitcoin, but it is the first of its breed, a prototype, and vulnerable to more highly-evolved competitors. At present, any threatening rivals have yet to rear its head; Bitcoin remains the first and foremost private virtual currency, but we can offer no guarantees that it will retain that position. It would certainly be in keeping with internet history for similar system built from the same principles to supersede and cast Bitcoin into obsolescence, after time had revealed its major shortcomings. Friendster and Myspace suffered similar fates at the hand of Facebook, Napster was ousted by Limeware, Bearshare and torrent applications, and Skype has all but crushed the last few disciples of the Microsoft Messenger army.

This may sound rather foreboding, so bear in mind that introduction of new and possibly better virtual currencies will not necessarily herald Bitcoin's demise. If Bitcoin establishes itself sufficiently firmly before the inception of the next generation of private, online currencies as to gain widespread acceptance and general stability, future currencies may pose little threat even if they can claim superior design.

==Sending and Receiving Payments==

=== Why do I have to wait 10 minutes before I can spend money I received? ===

10 minutes is the average time taken to find a block. It can be significantly more or less time than that depending on luck; 10 minutes is simply the average case.

You can see how long all other recent transactions have taken here: [http://bitcoinstats.org/ BitcoinStats.org].

[[Blocks]] (shown as "confirmations" in the GUI) are how the Bitcoin achieves consensus on who owns what. Once a block is found everyone agrees that you now own those coins, so you can spend them again. Until then it's possible that some network nodes believe otherwise, if somebody is attempting to defraud the system by reversing a transaction. The more confirmations a transaction has, the less risk there is of a reversal. Only 6 blocks or 1 hour is enough to make reversal computationally impractical. This is dramatically better than credit cards which can see chargebacks occur up to three months after the original transaction!

Ten minutes was specifically chosen by [[Satoshi]] as a tradeoff between propagation time of new blocks in large networks and the amount of work wasted due to chain splits. For a more technical explanation, see Satoshi's [http://www.bitcoin.org/bitcoin.pdf original technical paper].

[[File:TransactionConfirmationTimesExample.PNG]]

=== Do you have to wait until my transactions are confirmed in order to buy or sell things with Bitcoin? ===

YES, you do, IF the transaction is non-recourse. The Bitcoin reference software does not display transactions as confirmed until six blocks have passed (confirmations). As transactions are burred in the chain they become increasingly non-reversible but are very reversible before the first confirmation. Two to six confirmations are recommended for non-recourse situations depending on the value of the transactions involved.

When people ask this question they are usually thinking about applications like supermarkets. This generally is a recourse situation: if somebody tries to double-spend on a face-to-face transaction it might work a few times, but probabalistically speaking eventually one of the double-spends will get noticed, and the penalty for shoplifting charges in most localities is calibrated to be several times worse than the proceeds of a single shoplifting event.

Double-spends might be a concern for something like a snack machine in a low-traffic area with no nearby security cameras. Such a machine shouldn't honor 0-confirmation payments, and should instead use some other mechanism of clearing Bitcoin or validating transactions against reversal, see the wiki article [[Myths#Point_of_sale_with_bitcoins_isn.27t_possible_because_of_the_10_minute_wait_for_confirmation|here]] for alternatives.

When people ask this question they are usually thinking about applications that require immediate payment processing, like supermarkets or snack machines. Here is one way to reverse an unconfirmed payment:

A [[Double-spending#Finney_attack|Finney attack]], in which an attacker mines a block containing a movement of some coins back to themselves. Once they find a block solution, they quickly go to a merchant and make a purchase, then broadcast the block, thus taking back the coins. This attack is a risk primarily for goods that are dispatched immediately, like song downloads or currency trades. Because the attacker can't choose the time of the attack, it isn't a risk for merchants such as supermarkets where you can't choose exactly when to pay (due to queues, etc). The attack can fail if somebody else finds a block containing the purchasing transaction before you release your own block, therefore, merchants can reduce but not eliminate the risk by making purchasers wait some length of time that's less than a confirm.

Because pulling off this attack is not trivial, merchants who need to sell things automatically and instantly are most likely to just price the cost of reversal fraud in, or use insurance.

=== I was sent some bitcoins and they haven't arrived yet! Where are they? ===

Don't panic! There are a number of reasons why your bitcoins might not show up yet, and a number of ways to diagnose them.

The latest version of the Bitcoin-Qt client tells you how far it has yet to go in downloading the blockchain. Hover over the icon in the bottom right corner of the client to learn your client's status.

If it has not caught up then it's possible that your transaction hasn't been included in a block yet.

You can check pending transactions in the network by going [http://blockchain.info here] and then searching for your address. If the transaction is listed here then it's a matter of waiting until it gets included in a block before it will show in your client.

Bear in mind that if the transaction is based on a coin that was in a recent transaction then it could be considered a low priority transaction take longer to transfer if the transaction fee paid isn't high enough. Very low priority transactions with 0 fees might take hours or days to be included in a block.

=== Why does my Bitcoin address keep changing? ===

Whenever the address listed in "Your address" receives a transaction, Bitcoin replaces it with a new address. This is meant to encourage you to use a new address for every transaction, which enhances [[anonymity]]. All of your old addresses are still usable: you can see them in ''Settings -> Your Receiving Addresses''.

===How much will the transaction fee be?===

Some transactions might require a [[transaction fee]] for them to get confirmed in a timely manner. The transaction fee is processed by and received by the bitcoin miner. The most recent version of the Bitcoin client will estimate an appropriate fee when a fee might be required.

The fee is added to the payment amount. For example, if you are sending a 1.234 BTC payment and the client requires a 0.0005 BTC fee, then 1.2345 BTC will be subtracted from the wallet balance for the entire transaction and the address for where the payment was sent will receive a payment of 1.234 BTC.

In cases where a fee is required it is required because your transaction objectively looks like a denial of service attack to the bitcoin system, either due to it being burdensome to transmit or it recycles bitcoins you recently received. The wallet software attempts to avoid generating burdensome transactions, but it isn't always able if the funds in your wallet are new or are composed of many very tiny payments.

Because the fee is related to the amount of data that makes up the transaction and not to the amount of bitcoins being sent, the fee may seem extremely low (0.0005 BTC for a 1,000 BTC transfer) or unfairly high (0.004 BTC for a 0.02 BTC payment, or about 20%). If you are receiving tiny amounts (e.g., as small payments from a mining pool) then fees when sending will be higher than if your activity follows a more normal consumer or business transaction pattern. As of bitcoin 0.5.3 the required fee it will ask for will not be higher than 0.05 BTC, though for most users there is usually no required fee at all and 0.0005 is the most common when one is required.

=== What happens when someone sends me a bitcoin but my computer is powered off? ===

Bitcoins aren't actually "sent" to your wallet, the software only uses that term so that we can use the currency without having to learn new concepts. Your wallet is only needed when you wish to spend coins that you've received.

The coins that were sent to you when the client was not running will later appear as if they were received in your wallet when you later launch the client. It will download blocks and catch up with any transactions it didn't already have.

=== How long does "synchronizing" take when the Bitcoin client is first installed? What's it doing? ===

The popular Bitcoin client software from bitcoin.org implements a "full" Bitcoin node: It can carry out all the duties of the Bitcoin P2P system, it isn't simply a "client". One of the principles behind the operation of full Bitcoin nodes is that they don't assume that the other participants have followed the rules of the Bitcoin system. During synchronization, the software is processing historical Bitcoin transactions and making sure for itself that all of the rules of the system have been correctly followed.

In normal operation, after synchronizing, the software should use a hardly noticeable amount of IO, CPU, or network capacity.

The initial validation is very disk-IO-intensive, so the amount of time to synchronize depends on your disk speed and, to a lesser extent, your CPU speed. It can take anywhere from a few hours to a day or so. You can use the software while this process is going on, but you may not see recent payments to you until the synchronization has caught up to the point where those transactions happened.

If this is too long for you, you can download a pre-synchronized blockchain from [http://eu1.bitcoincharts.com/blockchain/ http://eu1.bitcoincharts.com/blockchain/]. Alternatively, you can try an alternative "lite" client such as Multibit or a super-light client like electrum, though these clients have somewhat weaker security, are less mature, and don't contribute to the health of the P2P network.

==Networking==
=== Do I need to configure my firewall to run Bitcoin? ===

Bitcoin will connect to other nodes, usually on TCP port 8333. You will need to allow outgoing TCP connections to port 8333 if you want to allow your Bitcoin client to connect to many nodes. [[Testnet]] uses TCP port 18333 instead of 8333.

If you want to restrict your firewall rules to a few IPs, you can find stable nodes in the [[Fallback Nodes|fallback nodes list]].

=== How does the peer finding mechanism work? ===

Bitcoin finds peers primarily by forwarding peer announcements within its own network and each node saves a database of peers that it's aware of, for future use. In order to bootstrap this process Bitcoin needs a list of initial peers, these can be provided manually but normally it obtains them by querying a set of DNS domain names which have automatically updated lists, if that doesn't work it falls back to a build-in list which is updated from time to time in new versions of the software. There is also an IRC based mechanism but it is disabled by default.

==Mining==
===What is mining?===
[[Mining]] is the process of spending computation power to secure Bitcoin transactions against reversal and introducing new Bitcoins to the system.

Technically speaking, mining is the calculation of a [[hash]] of the a block header, which includes among other things a reference to the previous block, a hash of a set of transactions and a [[nonce]]. If the hash value is found to be less than the current [[target]] (which is inversely proportional to the [[difficulty]]), a new block is formed and the miner gets the newly generated Bitcoins (50 per block at current levels). If the hash is not less than the current target, a new nonce is tried, and a new hash is calculated. This is done millions of times per second by each miner.

===Is mining used for some useful computation?===
The computations done when mining are internal to Bitcoin and not related to any other distributed computing projects. They serve the purpose of securing the Bitcoin network, which is useful.

===Is it not a waste of energy?===
Spending energy on creating and securing a free monetary system is hardly a waste. Also, services necessary for the operation of currently widespread monetary systems, such as banks and credit card companies, also spend energy, arguably more than Bitcoin would.

===Why don't we use calculations that are also useful for some other purpose?===
To provide security for the Bitcoin network, the calculations involved need to have some very specific features. These features are incompatible with leveraging the computation for other purposes.

===How can we stop miners from creating zero transaction blocks?===
The incentive for miners to include transactions is in the fees that come along with them. If we were to implement some minimum number of transactions per block it would be trivial for a miner to create and include transactions merely to surpass that threshold. As the network matures, the block reward drops, and miners become more dependent on transactions fees to pay their costs, the problem of zero transaction blocks should diminish over time.

===How does the proof-of-work system help secure Bitcoin?===
To give a general idea of the mining process, imagine this setup:

payload = <some data related to things happening on the Bitcoin network>
nonce = 1
hash = [http://en.wikipedia.org/wiki/SHA2 SHA2]( [http://en.wikipedia.org/wiki/SHA2 SHA2]( payload + nonce ) )

The work performed by a miner consists of repeatedly increasing "nonce" until
the hash function yields a value, that has the rare property of being below a certain
target threshold. (In other words: The hash "starts with a certain number of zeroes",
if you display it in the fixed-length representation, that is typically used.)

As can be seen, the mining process doesn't compute anything special. It merely
tries to find a number (also referred to as nonce) which - in combination with the payload -
results in a hash with special properties.

The advantage of using such a mechanism consists of the fact, that it is very easy to check a result: Given the payload and a specific nonce, only a single call of the hashing function is needed to verify that the hash has the required properties. Since there is no known way to find these hashes other than brute force, this can be used as a "proof of work" that someone invested a lot of computing power to find the correct nonce for this payload.

This feature is then used in the Bitcoin network to secure various aspects. An attacker
that wants to introduce malicious payload data into the network, will need to do the
required proof of work before it will be accepted. And as long as honest miners have more
computing power, they can always outpace an attacker.

Also see [http://en.wikipedia.org/wiki/SHA2 SHA2] and [http://en.wikipedia.org/wiki/Proof-of-work_system Proof-of-work system] on Wikipedia.

===Why was the "Generate coin" option of the client software removed?===

In the early days of Bitcoin, it was easy for anyone to find new blocks using standard CPUs. As more and more people started mining, the [[difficulty]] of finding new blocks has greatly increased to the point where the average time for a CPU to find a single block can be many years. The only cost-effective method of [[Mining|mining]] is using a high-end graphics card with special software (see also [[Why a GPU mines faster than a CPU]]) and/or joining a [[Bitcoin Pool|mining pool]]. Since solo CPU mining is essentially useless, it was removed from the GUI of the Bitcoin software.

==Security==

===Could miners collude to give themselves money or to fundamentally change the nature of Bitcoin?===

There are two questions in here. Let's look at them separately.

;Could miners gang up and give themselves money?

Mining itself is the process of creating new blocks in the block chain. Each block contains a list of all the transactions that have taken place across the entire Bitcoin network since the last block was created, as well as a hash of the previous block. New blocks are 'mined', or rather, generated, by Bitcoin clients correctly guessing sequences of characters in codes called 'hashes,' which are created using information from previous blocks. Bitcoin users may download specialized 'mining' software, which allows them to dedicate some amount of their processing power – however large or small – to guessing at strings within the hash of the previous block. Whoever makes the right guess first, thus creating a new block, receives a reward in Bitcoins.

The block chain is one of the two structures that makes Bitcoin secure, the other being the public-key encryption system on which Bitcoin trade is based. The block chain assures that not only is every single transaction that ever takes place recorded, but that every single transaction is recorded on the computer of anyone who chooses to store the relevant information. Many, many users have complete records of every transaction in Bitcoins history readily available to them at any point, and anyone who wants in the information can obtain it with ease. These things make Bitcoin very hard to fool.

The Bitcoin network takes considerable processing power to run, and since those with the most processing power can make the most guesses, those who put the most power toward to sustaining the network earn the most currency. Each correct guess yields, at present, fifty Bitcoins, and as Bitcoins are presently worth something (although the value still fluctuates) every miner who earns any number of Bitcoins makes money. Some miners pull in Bitcoins on their own; and some also join or form pools wherein all who contribute earn a share of the profits.

Therefore, first answer is a vehement “yes” – no only can miners collude to get more money, Bitcoin is designed to encourage them to do so. Bitcoin pools are communal affairs, and there is nothing dishonest or underhanded about them.

Of course, the real question is:

;Can they do so in ways not sanction by Bitcoin developers? Is there any way to rip off the network and make loads of money dishonestly?

Bitcoin isn't infallible. It can be cheated, but doing so is extremely difficult. Bitcoin was designed to evade some of the central problems with modern currencies – namely, that their trustworthiness hinges upon that of people who might not have users' best interests in mind. Every currency in the world (other than Bitcoin) is controlled by large institutions who keep track of what's done with done with it, and who can manipulate its value. And every other currency has value because people trust the institutions that control them.

Bitcoin doesn't ask that its users trust any institution. Its security is based on the cryptography that is an integral part of its structure, and that is readily available for any and all to see. Instead of one entity keeping track of transactions, the entire network does, so Bitcoins are astoundingly difficult to steal, or double-spend. Bitcoins are created in a regular and predictable fashion, and by many different users, so no one can decide to make a whole lot more and lessen their value. In short, Bitcoin is designed to be inflation-proof, double-spend-proof and completely distributed.

Nonetheless, there are a few ways that one can acquire Bitcoins dishonestly. Firstly, one can steal private keys. Key theft isn't something that Bitcoin security has been designed to prevent: it's up to users to keep theirs safe. But the cryptography is designed so that it is completely impossible to deduce someone's private from their public one. As long as you keep your private key to yourself, you don't have much to worry about. Furthermore, one could theoretically create a new block chain, but due to the way in which the block chain is constructed, this would be extremely difficult and require massive amounts of processing power. A full explanation of the difficulties involved can be found in the [[block chain]] article.

Bitcoin can be ripped off – but doing so would be extremely hard and require considerable expertise and a staggering amount of processing power. And it's only going to get harder with time. Bitcoin isn't impenetrable, but it's close enough to put any real worries in the peripherals.

;Could miners fundamentally change the nature of Bitcoin?

Once again, almost certainly not.

Bitcoin is a distributed network, so any changes implemented to the system must be accepted by all users. Someone trying to change the way Bitcoins are generated would have to convince every user to download and use their software – so the only changes that would go through are those that would be equally benefit all users.

And thus, it is more or less impossible for anyone to change the function of Bitcoin to their advantage. If users don't like the changes, they won't adopt them, whereas if users do like them, then these will help everyone equally. Of course, one can conceive of a situation where someone manages to get a change pushed through that provides them with an advantage that no one notices, but given that Bitcoin is structurally relatively simple, it is unlikely that any major changes will go through without someone noticing first.

The fact that such changes are so difficult to make testifies to the fully distributed nature of Bitcoin. Any centrally controlled currency can be modified by its central agency without the consent of its adherents. Bitcoin has no central authority, so it changes only at the behest of the whole community. Bitcoins development represents a kind of collective evolution; the first of its kind among currencies.

==Help==
===I'd like to learn more. Where can I get help?===

* Read the [[Introduction|introduction to bitcoin]]
* See the videos, podcasts, and blog posts from the [[Press]]
* Read and post on the [[Bitcoin:Community_portal#Bitcoin_Community_Forums|forums]]
* Chat on one of the [[Bitcoin:Community_portal#IRC_Chat|Bitcoin IRC]] channels
* Listen to [http://omegataupodcast.net/2011/03/59-bitcoin-a-digital-decentralized-currency/ this podcast], which goes into the details of how bitcoin works
* Ask questions on the [http://bitcoin.stackexchange.com Bitcoin Stack Exchange]

==See Also==

* [[Man page]]
* [[Introduction]]

[[de:FAQ]]
[[zh-cn:FAQ]]
[[fr:FAQ]]
[[ru:FAQ]]

[[Category:Technical]]
[[Category:Vocabulary]]

Help:FAQ

2012-10-25T15:42:24Z

Jepo: /* How divisible are Bitcoins? */

Here you will find answers to the most commonly asked questions.

== General ==
=== What are bitcoins? ===
Bitcoins are the unit of currency of the Bitcoin system. A commonly used shorthand for this is “BTC” to refer to a price or amount (eg: “100 BTC”).
There are such things as [[physical bitcoins]], but ultimately, a bitcoin is just a number associated with a [[Address|Bitcoin Address]]. A physical bitcoin is simply an object, such as a coin, with the number carefully embedded inside. See also an [[Introduction|easy intro]] to bitcoin.

=== How can I get bitcoins? ===

There are a variety of ways to acquire bitcoins:

* Accept bitcoins as payment for goods or services.
* There are several services where you can [[buying bitcoins|trade them]] for traditional currency.
* Find someone to trade cash for bitcoins in-person through a [https://en.bitcoin.it/wiki/Category:Directories local directory].
* Participate in a [[Pooled mining|mining pool]].
* If you have a lot of mining hardware, you can solo mine and attempt to create a new [[block]] (currently yields 50 bitcoins).

===Does Bitcoin guarantee an influx of free money?===

Since Bitcoin is a new technology, what it is and how it works may be initially unclear. Bitcoin is sometimes presented as being one of three things:
<ol style="list-style-type: upper-alpha;">
<li>Some sort of online 'get-rich-quick' scam.</li>
<li>A loophole in the market economy, the installation of which guarantees a steady influx of cash.</li>
<li>A sure investment that will almost certainly yield a profit.</li>
</ol>
In fact, none of the above are true. Let's look at them independently.

;Is Bitcoin a 'get-rich-quick' scheme?
:If you've spent much time on the Internet, you've probably seen ads for many 'get-rich-quick' schemes. These ads usually promise huge profits for a small amounts of easy work. Such schemes are usually pyramid/matrix-style schemes that make money from their own employees and offer nothing of any real value. Most convince one to buy packages that will make them earn hundreds a day, which in fact have the buyer distribute more such ads, and make minute profits.

:Bitcoin is in no way similar to these schemes. Bitcoin doesn't promise windfall profits. There is no way for the developers to make money from your involvement or to take money from you. That bitcoins are nearly impossible to acquire without the owner's consent represents one of its greatest strengths. Bitcoin is an experimental, virtual currency that may succeed or may fail. None of its developers expect to get rich off of it.

:A more detailed answer to this question can be found [http://bitcointalk.org/?topic=7815.0 here].

;Will I make money by installing the client?
:Most people who use Bitcoin don't earn anything by doing so, and the default client has no built-in way to earn Bitcoins. A small minority of people with dedicated, high-performance hardware do earn some Bitcoins by "''mining''" (generating new bitcoins, see [[#What is mining?|What is mining?]]) with special software, but joining Bitcoin shouldn't be construed as being the road to riches. Most Bitcoin users get involved because they find the project conceptually interesting and don't earn anything by doing so. This is also why you won't find much speculation about the political or economic repercussions of Bitcoin anywhere on this site: Bitcoin developers owe their dedication to the project's intellectual yieldings more than to those of a monetary nature. Bitcoin is still taking its first baby steps; it may go on to do great things but right now it only has something to offer those chasing conceptually interesting projects or bleeding edge technology.

;As an investment, is Bitcoin a sure thing?
:Bitcoin is a new and interesting electronic currency, the value of which is not backed by any single government or organization. Like other currencies, it is worth something partly because people are willing to trade it for goods and services. Its exchange rate fluctuates continuously, and sometimes wildly. It lacks wide acceptance and is vulnerable to manipulation by parties with modest funding. Security incidents such as website and account compromise may trigger major sell-offs. Other fluctuations can build into positive feedback loops cause much larger exchange rate fluctuations. Anyone who puts money into Bitcoin should take measures to reduce their risk and consider it as a high-risk currency. Later, as Bitcoin becomes better known and more widely accepted, it should stabilize, but for the time being it is unpredictable. Any investment in Bitcoin should be done carefully and with a clear plan to manage risk.

=== Can I buy bitcoins with Paypal? ===

It is possible to buy [[physical bitcoins]] with PayPal but it is otherwise difficult and/or expensive to do so, because of significant risk to the seller.

While it is possible to find an individual who wishes to sell Bitcoin to you via Paypal, (perhaps via [http://www.bitcoin-otc.com/ #bitcoin-otc] ) most exchanges do not allow funding through PayPal. This is due to repeated cases where someone pays for bitcoins with Paypal receives their bitcoins, and then fraudulently complains to Paypal that they never received their purchase. PayPal often sides with the fraudulent buyer in this case which means any seller would need to cover that risk with higher fees or refuse to accept PayPal altogether.

Buying Bitcoins from individuals with this method is still possible, but requires the seller to have some trust that the buyer will not file a claim with PayPal to reverse the payment.

=== Where can I find a forum to discuss Bitcoin? ===

Please visit the [[Bitcoin:Community_portal#Bitcoin_Community_Forums_on_various_platforms|Community Portal]] for links to Bitcoin-related forums.

=== How are new bitcoins created? ===

[[File:total_bitcoins_over_time_graph.png|thumb|Number of bitcoins over time, assuming a perfect 10-minute interval.]]
New bitcoins are generated by the network through the process of "[[#What is mining?|''mining'']]". In a process that is similar to a continuous lottery, mining nodes on the network are awarded bitcoins each time they find the solution to a certain mathematical problem (and thereby create a new [[block]]). Creating a block is a [[proof of work]] with a difficulty that varies with the overall strength of the network. The reward for solving a block is [[Controlled Currency Supply|automatically adjusted]] so that in roughly the first four years of operation of the Bitcoin network, {{formatnum:10500000}} BTC will be created. This amount is halved each four years, so it will be {{formatnum:5250000}} over years 4-8, {{formatnum:2625000}} over years 8-12, and so on. Thus the total number of bitcoins in existence will not exceed {{formatnum:21000000}}. See [[Controlled Currency Supply]].

Blocks are [[Mining|mined]] every 10 minutes, on average and for the first four years ({{formatnum:210000}} blocks) each block includes 50 new bitcoins. As the amount of processing power directed at mining changes, the difficulty of creating new bitcoins changes. This difficulty factor is calculated every 2016 blocks and is based upon the time taken to generate the previous 2016 blocks. See [[Mining]].

=== What's the current total number of bitcoins in existence? ===

[http://blockexplorer.com/q/totalbc Current count]. Also see [https://blockchain.info/charts/total-bitcoins Total bitcoins in circulation chart]

The number of blocks times the coin value of a block is the number of coins in existence. The coin value of a block is 50 BTC for each of the first {{formatnum:210000}} blocks, 25 BTC for the next {{formatnum:210000}} blocks, then 12.5 BTC, 6.25 BTC and so on.

=== How divisible are bitcoins? ===

A bitcoin can be divided down to 8 decimal places. Therefore, 0.00000001 BTC is the smallest amount that can be handled in a transaction. If necessary, the protocol and related software can be modified to handle even smaller amounts.

=== What do I call the various denominations of Bitcoins? ===

There is a lot of discussion about the naming of these fractions of Bitcoins. The leading candidates are:

* 1 BTC = 1 Bitcoin
* 0.01 BTC = 1 cBTC = 1 Centi-Bitcoin (also referred to as Bitcent)
* 0.001 BTC = 1 mBTC = 1 Milli-Bitcoin (also referred to as mbit (pronounced em-bit) or millibit or even bitmill)
* 0.000 001 BTC = 1 μBTC = 1 Micro-Bitcoin (also referred to as ubit (pronounced yu-bit) or microbit)

The above follows the accepted international SI prefixes for hundredths, thousandths, and millionths. There are many arguments against the special case of 0.01 BTC since it is unlikely to represent anything meaningful as the Bitcoin economy grows (it certainly won't be the equivalent of 0.01 USD, GBP or EUR). Equally, the inclusion of existing national currency denominations such as "cent", "nickel", "dime", "pence", "pound", "kopek" and so on are to be discouraged. This is a worldwide currency.

One exception is the "satoshi" which is smallest denomination currently possible

* 0.000 000 01 BTC = 1 Satoshi (pronounced sa-toh-shee)

which is so named in honour of Satoshi Nakamoto the pseudonym of the inventor of Bitcoin.

For an overview of all defined units of Bitcoin (including less common and niche units), see [[Units]].

Further discussion on this topic can be found on the forums here:

* [http://forum.bitcoin.org/index.php?topic=14438.msg195287#msg195287 We need names]
* [http://forum.bitcoin.org/index.php?topic=8282.0 What to call 0.001 BTC]

=== How does the halving work when the number gets really small? ===

Eventually the reward will go from 0.00000001 BTC to zero and no more bitcoins will be created.

The block reward calculation is done as a right bitwise shift of a 64-bit signed integer, which means it is divided by two and rounded down. The integer is equal to the value in BTC * 100,000,000 since internally in the reference client software, all Bitcoin balances and values are stored as unsigned integers.

With an initial block reward of 50 BTC, it will take many 4-year periods for the block reward to reach zero.

=== How long will it take to generate all the coins? ===

The last block that will generate coins will be block #6,929,999 which should be generated at or near the year 2140. The total number of coins in circulation will then remain static at 20,999,999.9769 BTC.

Even if the allowed precision is expanded from the current 8 decimals, the total BTC in circulation will always be slightly below 21 million (assuming everything else stays the same). For example, with 16 decimals of precision, the end total would be 20,999,999.999999999496 BTC.

=== If no more coins are going to be generated, will more blocks be created? ===

Absolutely! Even before the creation of coins ends, the use of [[transaction fee|transaction fees]] will likely make creating new blocks more valuable from the fees than the new coins being created. When coin generation ends, these fees will sustain the ability to use bitcoins and the Bitcoin network. There is no practical limit on the number of blocks that will be mined in the future.

=== But if no more coins are generated, what happens when Bitcoins are lost? Won't that be a problem? ===

Because of the law of supply and demand, when fewer bitcoins are available the ones that are left will be in higher demand, and therefore will have a higher value. So, as Bitcoins are lost, the remaining bitcoins will eventually increase in value to compensate. As the value of a bitcoin increases, the number of bitcoins required to purchase an item '''de'''creases. This is a [[Deflationary spiral|deflationary economic model]]. As the average transaction size reduces, transactions will probably be denominated in sub-units of a bitcoin such as millibitcoins ("Millies") or microbitcoins ("Mikes").

The Bitcoin protocol uses a base unit of one hundred-millionth of a Bitcoin ("a Satoshi"), but unused bits are available in the protocol fields that could be used to denote even smaller subdivisions.

=== If every transaction is broadcast via the network, does Bitcoin scale? ===
The Bitcoin protocol allows lightweight clients that can use Bitcoin without downloading the entire transaction history. As traffic grows and this becomes more critical, implementations of the concept will be developed. Full network nodes will at some point become a more specialized service.

With some modifications to the software, full Bitcoin nodes could easily keep up with both VISA and MasterCard combined, using only fairly modest hardware (a single high end server by todays standards). It is worth noting that the MasterCard network is structured somewhat like Bitcoin itself - as a peer to peer broadcast network.

Learn more about [[Scalability]].

==Economy==
=== Where does the value of Bitcoin stem from? What backs up Bitcoin? ===
Bitcoins have value because they are useful and because they are [[Controlled Currency Supply|scarce]]. As they are accepted by more merchants, their value will [http://en.wikipedia.org/wiki/Sticky_%28economics%29 stabilize]. See the [[Trade|list of Bitcoin-accepting sites]].

When we say that a currency is backed up by gold, we mean that there's a promise in place that you can exchange the currency for gold. Bitcoins, like dollars and euros, are not backed up by anything except the variety of merchants that accept them.

It's a common misconception that Bitcoins gain their value from the cost of electricity required to generate them. Cost doesn't equal value – hiring 1,000 men to shovel a big hole in the ground may be costly, but not valuable. Also, even though scarcity is a critical requirement for a useful currency, it alone doesn't make anything valuable. For example, your fingerprints are scarce, but that doesn't mean they have any exchange value.

=== Is Bitcoin a bubble? ===
Yes, in the same way as the euro and dollar are. They only have value in exchange and have no inherent value. If everyone suddenly stopped accepting your dollars, euros or bitcoins, the "bubble" would burst and their value would drop to zero. But that is unlikely to happen: even in Somalia, where the government collapsed 20 years ago, [http://en.wikipedia.org/wiki/Somali_shilling Somali shillings] are still accepted as payment.

=== Is Bitcoin a Ponzi scheme? ===
In a Ponzi Scheme, the founders persuade investors that they’ll profit. Bitcoin does not make such a guarantee. There is no central entity, just individuals building an economy.

A ponzi scheme is a zero sum game. Early adopters can only profit at the expense of late adopters. Bitcoin has possible win-win outcomes. Early adopters profit from the rise in value. Late adopters, and indeed, society as a whole, benefit from the usefulness of a stable, fast, inexpensive, and widely accepted p2p currency.

The fact that early adopters benefit more doesn't alone make anything a Ponzi scheme. All good investments in successful companies have this quality.

=== Doesn't Bitcoin unfairly benefit early adopters? ===
Early adopters have a large number of bitcoins now because they took a risk and invested resources in an unproven technology. By so doing, they have helped Bitcoin become what it is now and what it will be in the future (hopefully, a ubiquitous decentralized digital currency). It is only fair they will reap the benefits of their successful investment.

In any case, any bitcoin generated will probably change hands dozens of time as a medium of exchange, so the profit made from the initial distribution will be insignificant compared to the total commerce enabled by Bitcoin.

Since the pricing of Bitcoins has fallen greatly from its June 2011 peak, prices today are much more similar to those enjoyed by many early adopters. Those who are buying Bitcoins today likely believe that Bitcoin will grow significantly in the future. Setting aside the brief opportunity to have sold Bitcoins at the June 2011 peak enjoyed by few, the early-adopter window is arguably still open.

===Won't loss of wallets and the finite amount of Bitcoins create excessive deflation, destroying Bitcoin? ===
Worries about Bitcoin being destroyed by deflation are not entirely unfounded. Unlike most currencies, which experience inflation as their founding institutions create more and more units, Bitcoin will likely experience gradual deflation with the passage of time. Bitcoin is unique in that only a small amount of units will ever be produced (twenty-one million to be exact), this number has been known since the project's inception, and the units are created at a predicable rate.

Also, Bitcoin users are faced with a danger that doesn't threaten users of any other currency: if a Bitcoin user loses his wallet, his money is gone forever, unless he finds it again. And not just to him; it's gone completely out of circulation, rendered utterly inaccessible to anyone. As people will lose their wallets, the total number of Bitcoins will slowly decrease.

Therefore, Bitcoin seems to be faced with a unique problem. Whereas most currencies inflate over time, Bitcoin will mostly likely do the just the opposite. Time will see the irretrievable loss of an ever-increasing number of Bitcoins. An already small number will be permanently whittled down further and further. And as there become fewer and fewer Bitcoins, the laws of supply and demand suggest that their value will probably continually rise.

Thus Bitcoin is bound to once again stray into mysterious territory, because no one exactly knows what happens to a currency that grows continually more valuable. Economists generally agree that a low level of inflation is a good thing for a currency, but nobody is quite sure about what might happens to one that continually deflates. Although deflation could hardly be called a rare phenomenon, steady, constant deflation is unheard of. There may be a lot of speculation, no one has any hard data to back up their claims.

That being said, there is a mechanism in place to combat the obvious consequences. Extreme deflation would render most currencies highly impractical: if a single Canadian dollar could suddenly buy the holder a car, how would one go about buying bread or candy? Even pennies would fetch more than a person could carry. Bitcoin, however, offers a simple and stylish solution: infinite divisibility. Bitcoins can be divided up and trade into as small of pieces as one wants, so no matter how valuable Bitcoins become, one can trade them in practical quantities.

In fact, infinite divisibility should allow Bitcoins to function in cases of extreme wallet loss. Even if, in the far future, so many people have lost their wallets that only a single Bitcoin, or a fraction of one, remains, Bitcoin should continue to function just fine. No one can claim to be sure what is going to happen, but deflation may prove to present a smaller threat than many expect.

For more information, see the [[Deflationary spiral]] page.

=== What if someone bought up all the existing Bitcoins? ===
Bitcoin markets are competitive -- meaning the price of a bitcoin will rise or fall depending on supply and demand at certain price levels. Only a fraction of bitcoins issued to date are found on the exchange markets for sale. So even though technically a buyer with lots of money could buy all the bitcoins offered for sale, unless those holding the rest of the bitcoins offer them for sale as well, even the wealthiest, most determined buyer can't get at them.

Additionally, new currency continues to be issued daily and will continue to do so for decades though over time the rate at which they are issued declines to insignificant levels. Those who are mining aren't obligated to sell their bitcoins so not all bitcoins will make it to the markets even.

This situation doesn't suggest, however, that the markets aren't vulnerable to price manipulation. It doesn't take significant amounts of money to move the market price up or down and thus Bitcoin remains a volatile asset.

===What if someone creates a new block chain, or a new digital currency that renders Bitcoin obsolete?===

That the block chain cannot be easily forked represents one of the central security mechanisms of Bitcoin. Given the choice between two block chains, a Bitcoin miner always chooses the longer one - that is to say, the one with the more complex hash. Thusly, it ensures that each user can only spend their bitcoins once, and that no user gets ripped off.

As a consequence of the block chain structure, there may at any time be many different sub-branches, and the possibility always exists of a transaction being over-written by the longest branch, if it has been recorded in a shorter one. The older a transaction is though, the lower its chances of being over-written, and the higher of becoming permanent. Although the block chain prevents one from spending more Bitcoins than one has, it means that transactions can be accidentally nullified.

A new block chain would leave the network vulnerable to [[double-spending|double-spend]] attacks. However, the creation of a viable new chain presents considerable difficulty, and the possibility does not present much of a risk.

Bitcoin will always choose the longer Block Chain and determines the relative length of two branches by the complexities of their hashes. Since the hash of each new block is made from that of the block preceding it, to create a block with a more complex hash, one must be prepared to do more computation than has been done by the entire Bitcoin network from the fork point up to the newest of the blocks one is trying to supersede. Needless to say, such an undertaking would require a very large amount of processing power and since Bitcoin is continually growing and expanding, it will likely only require more with the passage of time.

A much more distinct and real threat to the Bitcoin use is the development of other, superior virtual currencies, which could supplant Bitcoin and render it obsolete and valueless.

A great deal of careful thought and ingenuity has gone into the development of Bitcoin, but it is the first of its breed, a prototype, and vulnerable to more highly-evolved competitors. At present, any threatening rivals have yet to rear its head; Bitcoin remains the first and foremost private virtual currency, but we can offer no guarantees that it will retain that position. It would certainly be in keeping with internet history for similar system built from the same principles to supersede and cast Bitcoin into obsolescence, after time had revealed its major shortcomings. Friendster and Myspace suffered similar fates at the hand of Facebook, Napster was ousted by Limeware, Bearshare and torrent applications, and Skype has all but crushed the last few disciples of the Microsoft Messenger army.

This may sound rather foreboding, so bear in mind that introduction of new and possibly better virtual currencies will not necessarily herald Bitcoin's demise. If Bitcoin establishes itself sufficiently firmly before the inception of the next generation of private, online currencies as to gain widespread acceptance and general stability, future currencies may pose little threat even if they can claim superior design.

==Sending and Receiving Payments==

=== Why do I have to wait 10 minutes before I can spend money I received? ===

10 minutes is the average time taken to find a block. It can be significantly more or less time than that depending on luck; 10 minutes is simply the average case.

You can see how long all other recent transactions have taken here: [http://bitcoinstats.org/ BitcoinStats.org].

[[Blocks]] (shown as "confirmations" in the GUI) are how the Bitcoin achieves consensus on who owns what. Once a block is found everyone agrees that you now own those coins, so you can spend them again. Until then it's possible that some network nodes believe otherwise, if somebody is attempting to defraud the system by reversing a transaction. The more confirmations a transaction has, the less risk there is of a reversal. Only 6 blocks or 1 hour is enough to make reversal computationally impractical. This is dramatically better than credit cards which can see chargebacks occur up to three months after the original transaction!

Ten minutes was specifically chosen by [[Satoshi]] as a tradeoff between propagation time of new blocks in large networks and the amount of work wasted due to chain splits. For a more technical explanation, see Satoshi's [http://www.bitcoin.org/bitcoin.pdf original technical paper].

[[File:TransactionConfirmationTimesExample.PNG]]

=== Do you have to wait until my transactions are confirmed in order to buy or sell things with Bitcoin? ===

YES, you do, IF the transaction is non-recourse. The Bitcoin reference software does not display transactions as confirmed until six blocks have passed (confirmations). As transactions are burred in the chain they become increasingly non-reversible but are very reversible before the first confirmation. Two to six confirmations are recommended for non-recourse situations depending on the value of the transactions involved.

When people ask this question they are usually thinking about applications like supermarkets. This generally is a recourse situation: if somebody tries to double-spend on a face-to-face transaction it might work a few times, but probabalistically speaking eventually one of the double-spends will get noticed, and the penalty for shoplifting charges in most localities is calibrated to be several times worse than the proceeds of a single shoplifting event.

Double-spends might be a concern for something like a snack machine in a low-traffic area with no nearby security cameras. Such a machine shouldn't honor 0-confirmation payments, and should instead use some other mechanism of clearing Bitcoin or validating transactions against reversal, see the wiki article [[Myths#Point_of_sale_with_bitcoins_isn.27t_possible_because_of_the_10_minute_wait_for_confirmation|here]] for alternatives.

When people ask this question they are usually thinking about applications that require immediate payment processing, like supermarkets or snack machines. Here is one way to reverse an unconfirmed payment:

A [[Double-spending#Finney_attack|Finney attack]], in which an attacker mines a block containing a movement of some coins back to themselves. Once they find a block solution, they quickly go to a merchant and make a purchase, then broadcast the block, thus taking back the coins. This attack is a risk primarily for goods that are dispatched immediately, like song downloads or currency trades. Because the attacker can't choose the time of the attack, it isn't a risk for merchants such as supermarkets where you can't choose exactly when to pay (due to queues, etc). The attack can fail if somebody else finds a block containing the purchasing transaction before you release your own block, therefore, merchants can reduce but not eliminate the risk by making purchasers wait some length of time that's less than a confirm.

Because pulling off this attack is not trivial, merchants who need to sell things automatically and instantly are most likely to just price the cost of reversal fraud in, or use insurance.

=== I was sent some bitcoins and they haven't arrived yet! Where are they? ===

Don't panic! There are a number of reasons why your bitcoins might not show up yet, and a number of ways to diagnose them.

The latest version of the Bitcoin-Qt client tells you how far it has yet to go in downloading the blockchain. Hover over the icon in the bottom right corner of the client to learn your client's status.

If it has not caught up then it's possible that your transaction hasn't been included in a block yet.

You can check pending transactions in the network by going [http://blockchain.info here] and then searching for your address. If the transaction is listed here then it's a matter of waiting until it gets included in a block before it will show in your client.

Bear in mind that if the transaction is based on a coin that was in a recent transaction then it could be considered a low priority transaction take longer to transfer if the transaction fee paid isn't high enough. Very low priority transactions with 0 fees might take hours or days to be included in a block.

=== Why does my Bitcoin address keep changing? ===

Whenever the address listed in "Your address" receives a transaction, Bitcoin replaces it with a new address. This is meant to encourage you to use a new address for every transaction, which enhances [[anonymity]]. All of your old addresses are still usable: you can see them in ''Settings -> Your Receiving Addresses''.

===How much will the transaction fee be?===

Some transactions might require a [[transaction fee]] for them to get confirmed in a timely manner. The transaction fee is processed by and received by the bitcoin miner. The most recent version of the Bitcoin client will estimate an appropriate fee when a fee might be required.

The fee is added to the payment amount. For example, if you are sending a 1.234 BTC payment and the client requires a 0.0005 BTC fee, then 1.2345 BTC will be subtracted from the wallet balance for the entire transaction and the address for where the payment was sent will receive a payment of 1.234 BTC.

In cases where a fee is required it is required because your transaction objectively looks like a denial of service attack to the bitcoin system, either due to it being burdensome to transmit or it recycles bitcoins you recently received. The wallet software attempts to avoid generating burdensome transactions, but it isn't always able if the funds in your wallet are new or are composed of many very tiny payments.

Because the fee is related to the amount of data that makes up the transaction and not to the amount of bitcoins being sent, the fee may seem extremely low (0.0005 BTC for a 1,000 BTC transfer) or unfairly high (0.004 BTC for a 0.02 BTC payment, or about 20%). If you are receiving tiny amounts (e.g., as small payments from a mining pool) then fees when sending will be higher than if your activity follows a more normal consumer or business transaction pattern. As of bitcoin 0.5.3 the required fee it will ask for will not be higher than 0.05 BTC, though for most users there is usually no required fee at all and 0.0005 is the most common when one is required.

=== What happens when someone sends me a bitcoin but my computer is powered off? ===

Bitcoins aren't actually "sent" to your wallet, the software only uses that term so that we can use the currency without having to learn new concepts. Your wallet is only needed when you wish to spend coins that you've received.

The coins that were sent to you when the client was not running will later appear as if they were received in your wallet when you later launch the client. It will download blocks and catch up with any transactions it didn't already have.

=== How long does "synchronizing" take when the Bitcoin client is first installed? What's it doing? ===

The popular Bitcoin client software from bitcoin.org implements a "full" Bitcoin node: It can carry out all the duties of the Bitcoin P2P system, it isn't simply a "client". One of the principles behind the operation of full Bitcoin nodes is that they don't assume that the other participants have followed the rules of the Bitcoin system. During synchronization, the software is processing historical Bitcoin transactions and making sure for itself that all of the rules of the system have been correctly followed.

In normal operation, after synchronizing, the software should use a hardly noticeable amount of IO, CPU, or network capacity.

The initial validation is very disk-IO-intensive, so the amount of time to synchronize depends on your disk speed and, to a lesser extent, your CPU speed. It can take anywhere from a few hours to a day or so. You can use the software while this process is going on, but you may not see recent payments to you until the synchronization has caught up to the point where those transactions happened.

If this is too long for you, you can download a pre-synchronized blockchain from [http://eu1.bitcoincharts.com/blockchain/ http://eu1.bitcoincharts.com/blockchain/]. Alternatively, you can try an alternative "lite" client such as Multibit or a super-light client like electrum, though these clients have somewhat weaker security, are less mature, and don't contribute to the health of the P2P network.

==Networking==
=== Do I need to configure my firewall to run Bitcoin? ===

Bitcoin will connect to other nodes, usually on TCP port 8333. You will need to allow outgoing TCP connections to port 8333 if you want to allow your Bitcoin client to connect to many nodes. [[Testnet]] uses TCP port 18333 instead of 8333.

If you want to restrict your firewall rules to a few IPs, you can find stable nodes in the [[Fallback Nodes|fallback nodes list]].

=== How does the peer finding mechanism work? ===

Bitcoin finds peers primarily by forwarding peer announcements within its own network and each node saves a database of peers that it's aware of, for future use. In order to bootstrap this process Bitcoin needs a list of initial peers, these can be provided manually but normally it obtains them by querying a set of DNS domain names which have automatically updated lists, if that doesn't work it falls back to a build-in list which is updated from time to time in new versions of the software. There is also an IRC based mechanism but it is disabled by default.

==Mining==
===What is mining?===
[[Mining]] is the process of spending computation power to secure Bitcoin transactions against reversal and introducing new Bitcoins to the system.

Technically speaking, mining is the calculation of a [[hash]] of the a block header, which includes among other things a reference to the previous block, a hash of a set of transactions and a [[nonce]]. If the hash value is found to be less than the current [[target]] (which is inversely proportional to the [[difficulty]]), a new block is formed and the miner gets the newly generated Bitcoins (50 per block at current levels). If the hash is not less than the current target, a new nonce is tried, and a new hash is calculated. This is done millions of times per second by each miner.

===Is mining used for some useful computation?===
The computations done when mining are internal to Bitcoin and not related to any other distributed computing projects. They serve the purpose of securing the Bitcoin network, which is useful.

===Is it not a waste of energy?===
Spending energy on creating and securing a free monetary system is hardly a waste. Also, services necessary for the operation of currently widespread monetary systems, such as banks and credit card companies, also spend energy, arguably more than Bitcoin would.

===Why don't we use calculations that are also useful for some other purpose?===
To provide security for the Bitcoin network, the calculations involved need to have some very specific features. These features are incompatible with leveraging the computation for other purposes.

===How can we stop miners from creating zero transaction blocks?===
The incentive for miners to include transactions is in the fees that come along with them. If we were to implement some minimum number of transactions per block it would be trivial for a miner to create and include transactions merely to surpass that threshold. As the network matures, the block reward drops, and miners become more dependent on transactions fees to pay their costs, the problem of zero transaction blocks should diminish over time.

===How does the proof-of-work system help secure Bitcoin?===
To give a general idea of the mining process, imagine this setup:

payload = <some data related to things happening on the Bitcoin network>
nonce = 1
hash = [http://en.wikipedia.org/wiki/SHA2 SHA2]( [http://en.wikipedia.org/wiki/SHA2 SHA2]( payload + nonce ) )

The work performed by a miner consists of repeatedly increasing "nonce" until
the hash function yields a value, that has the rare property of being below a certain
target threshold. (In other words: The hash "starts with a certain number of zeroes",
if you display it in the fixed-length representation, that is typically used.)

As can be seen, the mining process doesn't compute anything special. It merely
tries to find a number (also referred to as nonce) which - in combination with the payload -
results in a hash with special properties.

The advantage of using such a mechanism consists of the fact, that it is very easy to check a result: Given the payload and a specific nonce, only a single call of the hashing function is needed to verify that the hash has the required properties. Since there is no known way to find these hashes other than brute force, this can be used as a "proof of work" that someone invested a lot of computing power to find the correct nonce for this payload.

This feature is then used in the Bitcoin network to secure various aspects. An attacker
that wants to introduce malicious payload data into the network, will need to do the
required proof of work before it will be accepted. And as long as honest miners have more
computing power, they can always outpace an attacker.

Also see [http://en.wikipedia.org/wiki/SHA2 SHA2] and [http://en.wikipedia.org/wiki/Proof-of-work_system Proof-of-work system] on Wikipedia.

===Why was the "Generate coin" option of the client software removed?===

In the early days of Bitcoin, it was easy for anyone to find new blocks using standard CPUs. As more and more people started mining, the [[difficulty]] of finding new blocks has greatly increased to the point where the average time for a CPU to find a single block can be many years. The only cost-effective method of [[Mining|mining]] is using a high-end graphics card with special software (see also [[Why a GPU mines faster than a CPU]]) and/or joining a [[Bitcoin Pool|mining pool]]. Since solo CPU mining is essentially useless, it was removed from the GUI of the Bitcoin software.

==Security==

===Could miners collude to give themselves money or to fundamentally change the nature of Bitcoin?===

There are two questions in here. Let's look at them separately.

;Could miners gang up and give themselves money?

Mining itself is the process of creating new blocks in the block chain. Each block contains a list of all the transactions that have taken place across the entire Bitcoin network since the last block was created, as well as a hash of the previous block. New blocks are 'mined', or rather, generated, by Bitcoin clients correctly guessing sequences of characters in codes called 'hashes,' which are created using information from previous blocks. Bitcoin users may download specialized 'mining' software, which allows them to dedicate some amount of their processing power – however large or small – to guessing at strings within the hash of the previous block. Whoever makes the right guess first, thus creating a new block, receives a reward in Bitcoins.

The block chain is one of the two structures that makes Bitcoin secure, the other being the public-key encryption system on which Bitcoin trade is based. The block chain assures that not only is every single transaction that ever takes place recorded, but that every single transaction is recorded on the computer of anyone who chooses to store the relevant information. Many, many users have complete records of every transaction in Bitcoins history readily available to them at any point, and anyone who wants in the information can obtain it with ease. These things make Bitcoin very hard to fool.

The Bitcoin network takes considerable processing power to run, and since those with the most processing power can make the most guesses, those who put the most power toward to sustaining the network earn the most currency. Each correct guess yields, at present, fifty Bitcoins, and as Bitcoins are presently worth something (although the value still fluctuates) every miner who earns any number of Bitcoins makes money. Some miners pull in Bitcoins on their own; and some also join or form pools wherein all who contribute earn a share of the profits.

Therefore, first answer is a vehement “yes” – no only can miners collude to get more money, Bitcoin is designed to encourage them to do so. Bitcoin pools are communal affairs, and there is nothing dishonest or underhanded about them.

Of course, the real question is:

;Can they do so in ways not sanction by Bitcoin developers? Is there any way to rip off the network and make loads of money dishonestly?

Bitcoin isn't infallible. It can be cheated, but doing so is extremely difficult. Bitcoin was designed to evade some of the central problems with modern currencies – namely, that their trustworthiness hinges upon that of people who might not have users' best interests in mind. Every currency in the world (other than Bitcoin) is controlled by large institutions who keep track of what's done with done with it, and who can manipulate its value. And every other currency has value because people trust the institutions that control them.

Bitcoin doesn't ask that its users trust any institution. Its security is based on the cryptography that is an integral part of its structure, and that is readily available for any and all to see. Instead of one entity keeping track of transactions, the entire network does, so Bitcoins are astoundingly difficult to steal, or double-spend. Bitcoins are created in a regular and predictable fashion, and by many different users, so no one can decide to make a whole lot more and lessen their value. In short, Bitcoin is designed to be inflation-proof, double-spend-proof and completely distributed.

Nonetheless, there are a few ways that one can acquire Bitcoins dishonestly. Firstly, one can steal private keys. Key theft isn't something that Bitcoin security has been designed to prevent: it's up to users to keep theirs safe. But the cryptography is designed so that it is completely impossible to deduce someone's private from their public one. As long as you keep your private key to yourself, you don't have much to worry about. Furthermore, one could theoretically create a new block chain, but due to the way in which the block chain is constructed, this would be extremely difficult and require massive amounts of processing power. A full explanation of the difficulties involved can be found in the [[block chain]] article.

Bitcoin can be ripped off – but doing so would be extremely hard and require considerable expertise and a staggering amount of processing power. And it's only going to get harder with time. Bitcoin isn't impenetrable, but it's close enough to put any real worries in the peripherals.

;Could miners fundamentally change the nature of Bitcoin?

Once again, almost certainly not.

Bitcoin is a distributed network, so any changes implemented to the system must be accepted by all users. Someone trying to change the way Bitcoins are generated would have to convince every user to download and use their software – so the only changes that would go through are those that would be equally benefit all users.

And thus, it is more or less impossible for anyone to change the function of Bitcoin to their advantage. If users don't like the changes, they won't adopt them, whereas if users do like them, then these will help everyone equally. Of course, one can conceive of a situation where someone manages to get a change pushed through that provides them with an advantage that no one notices, but given that Bitcoin is structurally relatively simple, it is unlikely that any major changes will go through without someone noticing first.

The fact that such changes are so difficult to make testifies to the fully distributed nature of Bitcoin. Any centrally controlled currency can be modified by its central agency without the consent of its adherents. Bitcoin has no central authority, so it changes only at the behest of the whole community. Bitcoins development represents a kind of collective evolution; the first of its kind among currencies.

==Help==
===I'd like to learn more. Where can I get help?===

* Read the [[Introduction|introduction to bitcoin]]
* See the videos, podcasts, and blog posts from the [[Press]]
* Read and post on the [[Bitcoin:Community_portal#Bitcoin_Community_Forums|forums]]
* Chat on one of the [[Bitcoin:Community_portal#IRC_Chat|Bitcoin IRC]] channels
* Listen to [http://omegataupodcast.net/2011/03/59-bitcoin-a-digital-decentralized-currency/ this podcast], which goes into the details of how bitcoin works
* Ask questions on the [http://bitcoin.stackexchange.com Bitcoin Stack Exchange]

==See Also==

* [[Man page]]
* [[Introduction]]

[[de:FAQ]]
[[zh-cn:FAQ]]
[[fr:FAQ]]
[[ru:FAQ]]

[[Category:Technical]]
[[Category:Vocabulary]]

Help:FAQ

2012-10-25T15:41:45Z

Jepo: /* What's the current total number of Bitcoins in existence? */

Here you will find answers to the most commonly asked questions.

== General ==
=== What are bitcoins? ===
Bitcoins are the unit of currency of the Bitcoin system. A commonly used shorthand for this is “BTC” to refer to a price or amount (eg: “100 BTC”).
There are such things as [[physical bitcoins]], but ultimately, a bitcoin is just a number associated with a [[Address|Bitcoin Address]]. A physical bitcoin is simply an object, such as a coin, with the number carefully embedded inside. See also an [[Introduction|easy intro]] to bitcoin.

=== How can I get bitcoins? ===

There are a variety of ways to acquire bitcoins:

* Accept bitcoins as payment for goods or services.
* There are several services where you can [[buying bitcoins|trade them]] for traditional currency.
* Find someone to trade cash for bitcoins in-person through a [https://en.bitcoin.it/wiki/Category:Directories local directory].
* Participate in a [[Pooled mining|mining pool]].
* If you have a lot of mining hardware, you can solo mine and attempt to create a new [[block]] (currently yields 50 bitcoins).

===Does Bitcoin guarantee an influx of free money?===

Since Bitcoin is a new technology, what it is and how it works may be initially unclear. Bitcoin is sometimes presented as being one of three things:
<ol style="list-style-type: upper-alpha;">
<li>Some sort of online 'get-rich-quick' scam.</li>
<li>A loophole in the market economy, the installation of which guarantees a steady influx of cash.</li>
<li>A sure investment that will almost certainly yield a profit.</li>
</ol>
In fact, none of the above are true. Let's look at them independently.

;Is Bitcoin a 'get-rich-quick' scheme?
:If you've spent much time on the Internet, you've probably seen ads for many 'get-rich-quick' schemes. These ads usually promise huge profits for a small amounts of easy work. Such schemes are usually pyramid/matrix-style schemes that make money from their own employees and offer nothing of any real value. Most convince one to buy packages that will make them earn hundreds a day, which in fact have the buyer distribute more such ads, and make minute profits.

:Bitcoin is in no way similar to these schemes. Bitcoin doesn't promise windfall profits. There is no way for the developers to make money from your involvement or to take money from you. That bitcoins are nearly impossible to acquire without the owner's consent represents one of its greatest strengths. Bitcoin is an experimental, virtual currency that may succeed or may fail. None of its developers expect to get rich off of it.

:A more detailed answer to this question can be found [http://bitcointalk.org/?topic=7815.0 here].

;Will I make money by installing the client?
:Most people who use Bitcoin don't earn anything by doing so, and the default client has no built-in way to earn Bitcoins. A small minority of people with dedicated, high-performance hardware do earn some Bitcoins by "''mining''" (generating new bitcoins, see [[#What is mining?|What is mining?]]) with special software, but joining Bitcoin shouldn't be construed as being the road to riches. Most Bitcoin users get involved because they find the project conceptually interesting and don't earn anything by doing so. This is also why you won't find much speculation about the political or economic repercussions of Bitcoin anywhere on this site: Bitcoin developers owe their dedication to the project's intellectual yieldings more than to those of a monetary nature. Bitcoin is still taking its first baby steps; it may go on to do great things but right now it only has something to offer those chasing conceptually interesting projects or bleeding edge technology.

;As an investment, is Bitcoin a sure thing?
:Bitcoin is a new and interesting electronic currency, the value of which is not backed by any single government or organization. Like other currencies, it is worth something partly because people are willing to trade it for goods and services. Its exchange rate fluctuates continuously, and sometimes wildly. It lacks wide acceptance and is vulnerable to manipulation by parties with modest funding. Security incidents such as website and account compromise may trigger major sell-offs. Other fluctuations can build into positive feedback loops cause much larger exchange rate fluctuations. Anyone who puts money into Bitcoin should take measures to reduce their risk and consider it as a high-risk currency. Later, as Bitcoin becomes better known and more widely accepted, it should stabilize, but for the time being it is unpredictable. Any investment in Bitcoin should be done carefully and with a clear plan to manage risk.

=== Can I buy bitcoins with Paypal? ===

It is possible to buy [[physical bitcoins]] with PayPal but it is otherwise difficult and/or expensive to do so, because of significant risk to the seller.

While it is possible to find an individual who wishes to sell Bitcoin to you via Paypal, (perhaps via [http://www.bitcoin-otc.com/ #bitcoin-otc] ) most exchanges do not allow funding through PayPal. This is due to repeated cases where someone pays for bitcoins with Paypal receives their bitcoins, and then fraudulently complains to Paypal that they never received their purchase. PayPal often sides with the fraudulent buyer in this case which means any seller would need to cover that risk with higher fees or refuse to accept PayPal altogether.

Buying Bitcoins from individuals with this method is still possible, but requires the seller to have some trust that the buyer will not file a claim with PayPal to reverse the payment.

=== Where can I find a forum to discuss Bitcoin? ===

Please visit the [[Bitcoin:Community_portal#Bitcoin_Community_Forums_on_various_platforms|Community Portal]] for links to Bitcoin-related forums.

=== How are new bitcoins created? ===

[[File:total_bitcoins_over_time_graph.png|thumb|Number of bitcoins over time, assuming a perfect 10-minute interval.]]
New bitcoins are generated by the network through the process of "[[#What is mining?|''mining'']]". In a process that is similar to a continuous lottery, mining nodes on the network are awarded bitcoins each time they find the solution to a certain mathematical problem (and thereby create a new [[block]]). Creating a block is a [[proof of work]] with a difficulty that varies with the overall strength of the network. The reward for solving a block is [[Controlled Currency Supply|automatically adjusted]] so that in roughly the first four years of operation of the Bitcoin network, {{formatnum:10500000}} BTC will be created. This amount is halved each four years, so it will be {{formatnum:5250000}} over years 4-8, {{formatnum:2625000}} over years 8-12, and so on. Thus the total number of bitcoins in existence will not exceed {{formatnum:21000000}}. See [[Controlled Currency Supply]].

Blocks are [[Mining|mined]] every 10 minutes, on average and for the first four years ({{formatnum:210000}} blocks) each block includes 50 new bitcoins. As the amount of processing power directed at mining changes, the difficulty of creating new bitcoins changes. This difficulty factor is calculated every 2016 blocks and is based upon the time taken to generate the previous 2016 blocks. See [[Mining]].

=== What's the current total number of bitcoins in existence? ===

[http://blockexplorer.com/q/totalbc Current count]. Also see [https://blockchain.info/charts/total-bitcoins Total bitcoins in circulation chart]

The number of blocks times the coin value of a block is the number of coins in existence. The coin value of a block is 50 BTC for each of the first {{formatnum:210000}} blocks, 25 BTC for the next {{formatnum:210000}} blocks, then 12.5 BTC, 6.25 BTC and so on.

=== How divisible are Bitcoins? ===

A bitcoin can be divided down to 8 decimal places. Therefore, 0.00000001 BTC is the smallest amount that can be handled in a transaction. If necessary, the protocol and related software can be modified to handle even smaller amounts.

=== What do I call the various denominations of Bitcoins? ===

There is a lot of discussion about the naming of these fractions of Bitcoins. The leading candidates are:

* 1 BTC = 1 Bitcoin
* 0.01 BTC = 1 cBTC = 1 Centi-Bitcoin (also referred to as Bitcent)
* 0.001 BTC = 1 mBTC = 1 Milli-Bitcoin (also referred to as mbit (pronounced em-bit) or millibit or even bitmill)
* 0.000 001 BTC = 1 μBTC = 1 Micro-Bitcoin (also referred to as ubit (pronounced yu-bit) or microbit)

The above follows the accepted international SI prefixes for hundredths, thousandths, and millionths. There are many arguments against the special case of 0.01 BTC since it is unlikely to represent anything meaningful as the Bitcoin economy grows (it certainly won't be the equivalent of 0.01 USD, GBP or EUR). Equally, the inclusion of existing national currency denominations such as "cent", "nickel", "dime", "pence", "pound", "kopek" and so on are to be discouraged. This is a worldwide currency.

One exception is the "satoshi" which is smallest denomination currently possible

* 0.000 000 01 BTC = 1 Satoshi (pronounced sa-toh-shee)

which is so named in honour of Satoshi Nakamoto the pseudonym of the inventor of Bitcoin.

For an overview of all defined units of Bitcoin (including less common and niche units), see [[Units]].

Further discussion on this topic can be found on the forums here:

* [http://forum.bitcoin.org/index.php?topic=14438.msg195287#msg195287 We need names]
* [http://forum.bitcoin.org/index.php?topic=8282.0 What to call 0.001 BTC]

=== How does the halving work when the number gets really small? ===

Eventually the reward will go from 0.00000001 BTC to zero and no more bitcoins will be created.

The block reward calculation is done as a right bitwise shift of a 64-bit signed integer, which means it is divided by two and rounded down. The integer is equal to the value in BTC * 100,000,000 since internally in the reference client software, all Bitcoin balances and values are stored as unsigned integers.

With an initial block reward of 50 BTC, it will take many 4-year periods for the block reward to reach zero.

=== How long will it take to generate all the coins? ===

The last block that will generate coins will be block #6,929,999 which should be generated at or near the year 2140. The total number of coins in circulation will then remain static at 20,999,999.9769 BTC.

Even if the allowed precision is expanded from the current 8 decimals, the total BTC in circulation will always be slightly below 21 million (assuming everything else stays the same). For example, with 16 decimals of precision, the end total would be 20,999,999.999999999496 BTC.

=== If no more coins are going to be generated, will more blocks be created? ===

Absolutely! Even before the creation of coins ends, the use of [[transaction fee|transaction fees]] will likely make creating new blocks more valuable from the fees than the new coins being created. When coin generation ends, these fees will sustain the ability to use bitcoins and the Bitcoin network. There is no practical limit on the number of blocks that will be mined in the future.

=== But if no more coins are generated, what happens when Bitcoins are lost? Won't that be a problem? ===

Because of the law of supply and demand, when fewer bitcoins are available the ones that are left will be in higher demand, and therefore will have a higher value. So, as Bitcoins are lost, the remaining bitcoins will eventually increase in value to compensate. As the value of a bitcoin increases, the number of bitcoins required to purchase an item '''de'''creases. This is a [[Deflationary spiral|deflationary economic model]]. As the average transaction size reduces, transactions will probably be denominated in sub-units of a bitcoin such as millibitcoins ("Millies") or microbitcoins ("Mikes").

The Bitcoin protocol uses a base unit of one hundred-millionth of a Bitcoin ("a Satoshi"), but unused bits are available in the protocol fields that could be used to denote even smaller subdivisions.

=== If every transaction is broadcast via the network, does Bitcoin scale? ===
The Bitcoin protocol allows lightweight clients that can use Bitcoin without downloading the entire transaction history. As traffic grows and this becomes more critical, implementations of the concept will be developed. Full network nodes will at some point become a more specialized service.

With some modifications to the software, full Bitcoin nodes could easily keep up with both VISA and MasterCard combined, using only fairly modest hardware (a single high end server by todays standards). It is worth noting that the MasterCard network is structured somewhat like Bitcoin itself - as a peer to peer broadcast network.

Learn more about [[Scalability]].

==Economy==
=== Where does the value of Bitcoin stem from? What backs up Bitcoin? ===
Bitcoins have value because they are useful and because they are [[Controlled Currency Supply|scarce]]. As they are accepted by more merchants, their value will [http://en.wikipedia.org/wiki/Sticky_%28economics%29 stabilize]. See the [[Trade|list of Bitcoin-accepting sites]].

When we say that a currency is backed up by gold, we mean that there's a promise in place that you can exchange the currency for gold. Bitcoins, like dollars and euros, are not backed up by anything except the variety of merchants that accept them.

It's a common misconception that Bitcoins gain their value from the cost of electricity required to generate them. Cost doesn't equal value – hiring 1,000 men to shovel a big hole in the ground may be costly, but not valuable. Also, even though scarcity is a critical requirement for a useful currency, it alone doesn't make anything valuable. For example, your fingerprints are scarce, but that doesn't mean they have any exchange value.

=== Is Bitcoin a bubble? ===
Yes, in the same way as the euro and dollar are. They only have value in exchange and have no inherent value. If everyone suddenly stopped accepting your dollars, euros or bitcoins, the "bubble" would burst and their value would drop to zero. But that is unlikely to happen: even in Somalia, where the government collapsed 20 years ago, [http://en.wikipedia.org/wiki/Somali_shilling Somali shillings] are still accepted as payment.

=== Is Bitcoin a Ponzi scheme? ===
In a Ponzi Scheme, the founders persuade investors that they’ll profit. Bitcoin does not make such a guarantee. There is no central entity, just individuals building an economy.

A ponzi scheme is a zero sum game. Early adopters can only profit at the expense of late adopters. Bitcoin has possible win-win outcomes. Early adopters profit from the rise in value. Late adopters, and indeed, society as a whole, benefit from the usefulness of a stable, fast, inexpensive, and widely accepted p2p currency.

The fact that early adopters benefit more doesn't alone make anything a Ponzi scheme. All good investments in successful companies have this quality.

=== Doesn't Bitcoin unfairly benefit early adopters? ===
Early adopters have a large number of bitcoins now because they took a risk and invested resources in an unproven technology. By so doing, they have helped Bitcoin become what it is now and what it will be in the future (hopefully, a ubiquitous decentralized digital currency). It is only fair they will reap the benefits of their successful investment.

In any case, any bitcoin generated will probably change hands dozens of time as a medium of exchange, so the profit made from the initial distribution will be insignificant compared to the total commerce enabled by Bitcoin.

Since the pricing of Bitcoins has fallen greatly from its June 2011 peak, prices today are much more similar to those enjoyed by many early adopters. Those who are buying Bitcoins today likely believe that Bitcoin will grow significantly in the future. Setting aside the brief opportunity to have sold Bitcoins at the June 2011 peak enjoyed by few, the early-adopter window is arguably still open.

===Won't loss of wallets and the finite amount of Bitcoins create excessive deflation, destroying Bitcoin? ===
Worries about Bitcoin being destroyed by deflation are not entirely unfounded. Unlike most currencies, which experience inflation as their founding institutions create more and more units, Bitcoin will likely experience gradual deflation with the passage of time. Bitcoin is unique in that only a small amount of units will ever be produced (twenty-one million to be exact), this number has been known since the project's inception, and the units are created at a predicable rate.

Also, Bitcoin users are faced with a danger that doesn't threaten users of any other currency: if a Bitcoin user loses his wallet, his money is gone forever, unless he finds it again. And not just to him; it's gone completely out of circulation, rendered utterly inaccessible to anyone. As people will lose their wallets, the total number of Bitcoins will slowly decrease.

Therefore, Bitcoin seems to be faced with a unique problem. Whereas most currencies inflate over time, Bitcoin will mostly likely do the just the opposite. Time will see the irretrievable loss of an ever-increasing number of Bitcoins. An already small number will be permanently whittled down further and further. And as there become fewer and fewer Bitcoins, the laws of supply and demand suggest that their value will probably continually rise.

Thus Bitcoin is bound to once again stray into mysterious territory, because no one exactly knows what happens to a currency that grows continually more valuable. Economists generally agree that a low level of inflation is a good thing for a currency, but nobody is quite sure about what might happens to one that continually deflates. Although deflation could hardly be called a rare phenomenon, steady, constant deflation is unheard of. There may be a lot of speculation, no one has any hard data to back up their claims.

That being said, there is a mechanism in place to combat the obvious consequences. Extreme deflation would render most currencies highly impractical: if a single Canadian dollar could suddenly buy the holder a car, how would one go about buying bread or candy? Even pennies would fetch more than a person could carry. Bitcoin, however, offers a simple and stylish solution: infinite divisibility. Bitcoins can be divided up and trade into as small of pieces as one wants, so no matter how valuable Bitcoins become, one can trade them in practical quantities.

In fact, infinite divisibility should allow Bitcoins to function in cases of extreme wallet loss. Even if, in the far future, so many people have lost their wallets that only a single Bitcoin, or a fraction of one, remains, Bitcoin should continue to function just fine. No one can claim to be sure what is going to happen, but deflation may prove to present a smaller threat than many expect.

For more information, see the [[Deflationary spiral]] page.

=== What if someone bought up all the existing Bitcoins? ===
Bitcoin markets are competitive -- meaning the price of a bitcoin will rise or fall depending on supply and demand at certain price levels. Only a fraction of bitcoins issued to date are found on the exchange markets for sale. So even though technically a buyer with lots of money could buy all the bitcoins offered for sale, unless those holding the rest of the bitcoins offer them for sale as well, even the wealthiest, most determined buyer can't get at them.

Additionally, new currency continues to be issued daily and will continue to do so for decades though over time the rate at which they are issued declines to insignificant levels. Those who are mining aren't obligated to sell their bitcoins so not all bitcoins will make it to the markets even.

This situation doesn't suggest, however, that the markets aren't vulnerable to price manipulation. It doesn't take significant amounts of money to move the market price up or down and thus Bitcoin remains a volatile asset.

===What if someone creates a new block chain, or a new digital currency that renders Bitcoin obsolete?===

That the block chain cannot be easily forked represents one of the central security mechanisms of Bitcoin. Given the choice between two block chains, a Bitcoin miner always chooses the longer one - that is to say, the one with the more complex hash. Thusly, it ensures that each user can only spend their bitcoins once, and that no user gets ripped off.

As a consequence of the block chain structure, there may at any time be many different sub-branches, and the possibility always exists of a transaction being over-written by the longest branch, if it has been recorded in a shorter one. The older a transaction is though, the lower its chances of being over-written, and the higher of becoming permanent. Although the block chain prevents one from spending more Bitcoins than one has, it means that transactions can be accidentally nullified.

A new block chain would leave the network vulnerable to [[double-spending|double-spend]] attacks. However, the creation of a viable new chain presents considerable difficulty, and the possibility does not present much of a risk.

Bitcoin will always choose the longer Block Chain and determines the relative length of two branches by the complexities of their hashes. Since the hash of each new block is made from that of the block preceding it, to create a block with a more complex hash, one must be prepared to do more computation than has been done by the entire Bitcoin network from the fork point up to the newest of the blocks one is trying to supersede. Needless to say, such an undertaking would require a very large amount of processing power and since Bitcoin is continually growing and expanding, it will likely only require more with the passage of time.

A much more distinct and real threat to the Bitcoin use is the development of other, superior virtual currencies, which could supplant Bitcoin and render it obsolete and valueless.

A great deal of careful thought and ingenuity has gone into the development of Bitcoin, but it is the first of its breed, a prototype, and vulnerable to more highly-evolved competitors. At present, any threatening rivals have yet to rear its head; Bitcoin remains the first and foremost private virtual currency, but we can offer no guarantees that it will retain that position. It would certainly be in keeping with internet history for similar system built from the same principles to supersede and cast Bitcoin into obsolescence, after time had revealed its major shortcomings. Friendster and Myspace suffered similar fates at the hand of Facebook, Napster was ousted by Limeware, Bearshare and torrent applications, and Skype has all but crushed the last few disciples of the Microsoft Messenger army.

This may sound rather foreboding, so bear in mind that introduction of new and possibly better virtual currencies will not necessarily herald Bitcoin's demise. If Bitcoin establishes itself sufficiently firmly before the inception of the next generation of private, online currencies as to gain widespread acceptance and general stability, future currencies may pose little threat even if they can claim superior design.

==Sending and Receiving Payments==

=== Why do I have to wait 10 minutes before I can spend money I received? ===

10 minutes is the average time taken to find a block. It can be significantly more or less time than that depending on luck; 10 minutes is simply the average case.

You can see how long all other recent transactions have taken here: [http://bitcoinstats.org/ BitcoinStats.org].

[[Blocks]] (shown as "confirmations" in the GUI) are how the Bitcoin achieves consensus on who owns what. Once a block is found everyone agrees that you now own those coins, so you can spend them again. Until then it's possible that some network nodes believe otherwise, if somebody is attempting to defraud the system by reversing a transaction. The more confirmations a transaction has, the less risk there is of a reversal. Only 6 blocks or 1 hour is enough to make reversal computationally impractical. This is dramatically better than credit cards which can see chargebacks occur up to three months after the original transaction!

Ten minutes was specifically chosen by [[Satoshi]] as a tradeoff between propagation time of new blocks in large networks and the amount of work wasted due to chain splits. For a more technical explanation, see Satoshi's [http://www.bitcoin.org/bitcoin.pdf original technical paper].

[[File:TransactionConfirmationTimesExample.PNG]]

=== Do you have to wait until my transactions are confirmed in order to buy or sell things with Bitcoin? ===

YES, you do, IF the transaction is non-recourse. The Bitcoin reference software does not display transactions as confirmed until six blocks have passed (confirmations). As transactions are burred in the chain they become increasingly non-reversible but are very reversible before the first confirmation. Two to six confirmations are recommended for non-recourse situations depending on the value of the transactions involved.

When people ask this question they are usually thinking about applications like supermarkets. This generally is a recourse situation: if somebody tries to double-spend on a face-to-face transaction it might work a few times, but probabalistically speaking eventually one of the double-spends will get noticed, and the penalty for shoplifting charges in most localities is calibrated to be several times worse than the proceeds of a single shoplifting event.

Double-spends might be a concern for something like a snack machine in a low-traffic area with no nearby security cameras. Such a machine shouldn't honor 0-confirmation payments, and should instead use some other mechanism of clearing Bitcoin or validating transactions against reversal, see the wiki article [[Myths#Point_of_sale_with_bitcoins_isn.27t_possible_because_of_the_10_minute_wait_for_confirmation|here]] for alternatives.

When people ask this question they are usually thinking about applications that require immediate payment processing, like supermarkets or snack machines. Here is one way to reverse an unconfirmed payment:

A [[Double-spending#Finney_attack|Finney attack]], in which an attacker mines a block containing a movement of some coins back to themselves. Once they find a block solution, they quickly go to a merchant and make a purchase, then broadcast the block, thus taking back the coins. This attack is a risk primarily for goods that are dispatched immediately, like song downloads or currency trades. Because the attacker can't choose the time of the attack, it isn't a risk for merchants such as supermarkets where you can't choose exactly when to pay (due to queues, etc). The attack can fail if somebody else finds a block containing the purchasing transaction before you release your own block, therefore, merchants can reduce but not eliminate the risk by making purchasers wait some length of time that's less than a confirm.

Because pulling off this attack is not trivial, merchants who need to sell things automatically and instantly are most likely to just price the cost of reversal fraud in, or use insurance.

=== I was sent some bitcoins and they haven't arrived yet! Where are they? ===

Don't panic! There are a number of reasons why your bitcoins might not show up yet, and a number of ways to diagnose them.

The latest version of the Bitcoin-Qt client tells you how far it has yet to go in downloading the blockchain. Hover over the icon in the bottom right corner of the client to learn your client's status.

If it has not caught up then it's possible that your transaction hasn't been included in a block yet.

You can check pending transactions in the network by going [http://blockchain.info here] and then searching for your address. If the transaction is listed here then it's a matter of waiting until it gets included in a block before it will show in your client.

Bear in mind that if the transaction is based on a coin that was in a recent transaction then it could be considered a low priority transaction take longer to transfer if the transaction fee paid isn't high enough. Very low priority transactions with 0 fees might take hours or days to be included in a block.

=== Why does my Bitcoin address keep changing? ===

Whenever the address listed in "Your address" receives a transaction, Bitcoin replaces it with a new address. This is meant to encourage you to use a new address for every transaction, which enhances [[anonymity]]. All of your old addresses are still usable: you can see them in ''Settings -> Your Receiving Addresses''.

===How much will the transaction fee be?===

Some transactions might require a [[transaction fee]] for them to get confirmed in a timely manner. The transaction fee is processed by and received by the bitcoin miner. The most recent version of the Bitcoin client will estimate an appropriate fee when a fee might be required.

The fee is added to the payment amount. For example, if you are sending a 1.234 BTC payment and the client requires a 0.0005 BTC fee, then 1.2345 BTC will be subtracted from the wallet balance for the entire transaction and the address for where the payment was sent will receive a payment of 1.234 BTC.

In cases where a fee is required it is required because your transaction objectively looks like a denial of service attack to the bitcoin system, either due to it being burdensome to transmit or it recycles bitcoins you recently received. The wallet software attempts to avoid generating burdensome transactions, but it isn't always able if the funds in your wallet are new or are composed of many very tiny payments.

Because the fee is related to the amount of data that makes up the transaction and not to the amount of bitcoins being sent, the fee may seem extremely low (0.0005 BTC for a 1,000 BTC transfer) or unfairly high (0.004 BTC for a 0.02 BTC payment, or about 20%). If you are receiving tiny amounts (e.g., as small payments from a mining pool) then fees when sending will be higher than if your activity follows a more normal consumer or business transaction pattern. As of bitcoin 0.5.3 the required fee it will ask for will not be higher than 0.05 BTC, though for most users there is usually no required fee at all and 0.0005 is the most common when one is required.

=== What happens when someone sends me a bitcoin but my computer is powered off? ===

Bitcoins aren't actually "sent" to your wallet, the software only uses that term so that we can use the currency without having to learn new concepts. Your wallet is only needed when you wish to spend coins that you've received.

The coins that were sent to you when the client was not running will later appear as if they were received in your wallet when you later launch the client. It will download blocks and catch up with any transactions it didn't already have.

=== How long does "synchronizing" take when the Bitcoin client is first installed? What's it doing? ===

The popular Bitcoin client software from bitcoin.org implements a "full" Bitcoin node: It can carry out all the duties of the Bitcoin P2P system, it isn't simply a "client". One of the principles behind the operation of full Bitcoin nodes is that they don't assume that the other participants have followed the rules of the Bitcoin system. During synchronization, the software is processing historical Bitcoin transactions and making sure for itself that all of the rules of the system have been correctly followed.

In normal operation, after synchronizing, the software should use a hardly noticeable amount of IO, CPU, or network capacity.

The initial validation is very disk-IO-intensive, so the amount of time to synchronize depends on your disk speed and, to a lesser extent, your CPU speed. It can take anywhere from a few hours to a day or so. You can use the software while this process is going on, but you may not see recent payments to you until the synchronization has caught up to the point where those transactions happened.

If this is too long for you, you can download a pre-synchronized blockchain from [http://eu1.bitcoincharts.com/blockchain/ http://eu1.bitcoincharts.com/blockchain/]. Alternatively, you can try an alternative "lite" client such as Multibit or a super-light client like electrum, though these clients have somewhat weaker security, are less mature, and don't contribute to the health of the P2P network.

==Networking==
=== Do I need to configure my firewall to run Bitcoin? ===

Bitcoin will connect to other nodes, usually on TCP port 8333. You will need to allow outgoing TCP connections to port 8333 if you want to allow your Bitcoin client to connect to many nodes. [[Testnet]] uses TCP port 18333 instead of 8333.

If you want to restrict your firewall rules to a few IPs, you can find stable nodes in the [[Fallback Nodes|fallback nodes list]].

=== How does the peer finding mechanism work? ===

Bitcoin finds peers primarily by forwarding peer announcements within its own network and each node saves a database of peers that it's aware of, for future use. In order to bootstrap this process Bitcoin needs a list of initial peers, these can be provided manually but normally it obtains them by querying a set of DNS domain names which have automatically updated lists, if that doesn't work it falls back to a build-in list which is updated from time to time in new versions of the software. There is also an IRC based mechanism but it is disabled by default.

==Mining==
===What is mining?===
[[Mining]] is the process of spending computation power to secure Bitcoin transactions against reversal and introducing new Bitcoins to the system.

Technically speaking, mining is the calculation of a [[hash]] of the a block header, which includes among other things a reference to the previous block, a hash of a set of transactions and a [[nonce]]. If the hash value is found to be less than the current [[target]] (which is inversely proportional to the [[difficulty]]), a new block is formed and the miner gets the newly generated Bitcoins (50 per block at current levels). If the hash is not less than the current target, a new nonce is tried, and a new hash is calculated. This is done millions of times per second by each miner.

===Is mining used for some useful computation?===
The computations done when mining are internal to Bitcoin and not related to any other distributed computing projects. They serve the purpose of securing the Bitcoin network, which is useful.

===Is it not a waste of energy?===
Spending energy on creating and securing a free monetary system is hardly a waste. Also, services necessary for the operation of currently widespread monetary systems, such as banks and credit card companies, also spend energy, arguably more than Bitcoin would.

===Why don't we use calculations that are also useful for some other purpose?===
To provide security for the Bitcoin network, the calculations involved need to have some very specific features. These features are incompatible with leveraging the computation for other purposes.

===How can we stop miners from creating zero transaction blocks?===
The incentive for miners to include transactions is in the fees that come along with them. If we were to implement some minimum number of transactions per block it would be trivial for a miner to create and include transactions merely to surpass that threshold. As the network matures, the block reward drops, and miners become more dependent on transactions fees to pay their costs, the problem of zero transaction blocks should diminish over time.

===How does the proof-of-work system help secure Bitcoin?===
To give a general idea of the mining process, imagine this setup:

payload = <some data related to things happening on the Bitcoin network>
nonce = 1
hash = [http://en.wikipedia.org/wiki/SHA2 SHA2]( [http://en.wikipedia.org/wiki/SHA2 SHA2]( payload + nonce ) )

The work performed by a miner consists of repeatedly increasing "nonce" until
the hash function yields a value, that has the rare property of being below a certain
target threshold. (In other words: The hash "starts with a certain number of zeroes",
if you display it in the fixed-length representation, that is typically used.)

As can be seen, the mining process doesn't compute anything special. It merely
tries to find a number (also referred to as nonce) which - in combination with the payload -
results in a hash with special properties.

The advantage of using such a mechanism consists of the fact, that it is very easy to check a result: Given the payload and a specific nonce, only a single call of the hashing function is needed to verify that the hash has the required properties. Since there is no known way to find these hashes other than brute force, this can be used as a "proof of work" that someone invested a lot of computing power to find the correct nonce for this payload.

This feature is then used in the Bitcoin network to secure various aspects. An attacker
that wants to introduce malicious payload data into the network, will need to do the
required proof of work before it will be accepted. And as long as honest miners have more
computing power, they can always outpace an attacker.

Also see [http://en.wikipedia.org/wiki/SHA2 SHA2] and [http://en.wikipedia.org/wiki/Proof-of-work_system Proof-of-work system] on Wikipedia.

===Why was the "Generate coin" option of the client software removed?===

In the early days of Bitcoin, it was easy for anyone to find new blocks using standard CPUs. As more and more people started mining, the [[difficulty]] of finding new blocks has greatly increased to the point where the average time for a CPU to find a single block can be many years. The only cost-effective method of [[Mining|mining]] is using a high-end graphics card with special software (see also [[Why a GPU mines faster than a CPU]]) and/or joining a [[Bitcoin Pool|mining pool]]. Since solo CPU mining is essentially useless, it was removed from the GUI of the Bitcoin software.

==Security==

===Could miners collude to give themselves money or to fundamentally change the nature of Bitcoin?===

There are two questions in here. Let's look at them separately.

;Could miners gang up and give themselves money?

Mining itself is the process of creating new blocks in the block chain. Each block contains a list of all the transactions that have taken place across the entire Bitcoin network since the last block was created, as well as a hash of the previous block. New blocks are 'mined', or rather, generated, by Bitcoin clients correctly guessing sequences of characters in codes called 'hashes,' which are created using information from previous blocks. Bitcoin users may download specialized 'mining' software, which allows them to dedicate some amount of their processing power – however large or small – to guessing at strings within the hash of the previous block. Whoever makes the right guess first, thus creating a new block, receives a reward in Bitcoins.

The block chain is one of the two structures that makes Bitcoin secure, the other being the public-key encryption system on which Bitcoin trade is based. The block chain assures that not only is every single transaction that ever takes place recorded, but that every single transaction is recorded on the computer of anyone who chooses to store the relevant information. Many, many users have complete records of every transaction in Bitcoins history readily available to them at any point, and anyone who wants in the information can obtain it with ease. These things make Bitcoin very hard to fool.

The Bitcoin network takes considerable processing power to run, and since those with the most processing power can make the most guesses, those who put the most power toward to sustaining the network earn the most currency. Each correct guess yields, at present, fifty Bitcoins, and as Bitcoins are presently worth something (although the value still fluctuates) every miner who earns any number of Bitcoins makes money. Some miners pull in Bitcoins on their own; and some also join or form pools wherein all who contribute earn a share of the profits.

Therefore, first answer is a vehement “yes” – no only can miners collude to get more money, Bitcoin is designed to encourage them to do so. Bitcoin pools are communal affairs, and there is nothing dishonest or underhanded about them.

Of course, the real question is:

;Can they do so in ways not sanction by Bitcoin developers? Is there any way to rip off the network and make loads of money dishonestly?

Bitcoin isn't infallible. It can be cheated, but doing so is extremely difficult. Bitcoin was designed to evade some of the central problems with modern currencies – namely, that their trustworthiness hinges upon that of people who might not have users' best interests in mind. Every currency in the world (other than Bitcoin) is controlled by large institutions who keep track of what's done with done with it, and who can manipulate its value. And every other currency has value because people trust the institutions that control them.

Bitcoin doesn't ask that its users trust any institution. Its security is based on the cryptography that is an integral part of its structure, and that is readily available for any and all to see. Instead of one entity keeping track of transactions, the entire network does, so Bitcoins are astoundingly difficult to steal, or double-spend. Bitcoins are created in a regular and predictable fashion, and by many different users, so no one can decide to make a whole lot more and lessen their value. In short, Bitcoin is designed to be inflation-proof, double-spend-proof and completely distributed.

Nonetheless, there are a few ways that one can acquire Bitcoins dishonestly. Firstly, one can steal private keys. Key theft isn't something that Bitcoin security has been designed to prevent: it's up to users to keep theirs safe. But the cryptography is designed so that it is completely impossible to deduce someone's private from their public one. As long as you keep your private key to yourself, you don't have much to worry about. Furthermore, one could theoretically create a new block chain, but due to the way in which the block chain is constructed, this would be extremely difficult and require massive amounts of processing power. A full explanation of the difficulties involved can be found in the [[block chain]] article.

Bitcoin can be ripped off – but doing so would be extremely hard and require considerable expertise and a staggering amount of processing power. And it's only going to get harder with time. Bitcoin isn't impenetrable, but it's close enough to put any real worries in the peripherals.

;Could miners fundamentally change the nature of Bitcoin?

Once again, almost certainly not.

Bitcoin is a distributed network, so any changes implemented to the system must be accepted by all users. Someone trying to change the way Bitcoins are generated would have to convince every user to download and use their software – so the only changes that would go through are those that would be equally benefit all users.

And thus, it is more or less impossible for anyone to change the function of Bitcoin to their advantage. If users don't like the changes, they won't adopt them, whereas if users do like them, then these will help everyone equally. Of course, one can conceive of a situation where someone manages to get a change pushed through that provides them with an advantage that no one notices, but given that Bitcoin is structurally relatively simple, it is unlikely that any major changes will go through without someone noticing first.

The fact that such changes are so difficult to make testifies to the fully distributed nature of Bitcoin. Any centrally controlled currency can be modified by its central agency without the consent of its adherents. Bitcoin has no central authority, so it changes only at the behest of the whole community. Bitcoins development represents a kind of collective evolution; the first of its kind among currencies.

==Help==
===I'd like to learn more. Where can I get help?===

* Read the [[Introduction|introduction to bitcoin]]
* See the videos, podcasts, and blog posts from the [[Press]]
* Read and post on the [[Bitcoin:Community_portal#Bitcoin_Community_Forums|forums]]
* Chat on one of the [[Bitcoin:Community_portal#IRC_Chat|Bitcoin IRC]] channels
* Listen to [http://omegataupodcast.net/2011/03/59-bitcoin-a-digital-decentralized-currency/ this podcast], which goes into the details of how bitcoin works
* Ask questions on the [http://bitcoin.stackexchange.com Bitcoin Stack Exchange]

==See Also==

* [[Man page]]
* [[Introduction]]

[[de:FAQ]]
[[zh-cn:FAQ]]
[[fr:FAQ]]
[[ru:FAQ]]

[[Category:Technical]]
[[Category:Vocabulary]]

Help:FAQ

2012-10-25T15:40:12Z

Jepo: /* How are new bitcoins created? */

Here you will find answers to the most commonly asked questions.

== General ==
=== What are bitcoins? ===
Bitcoins are the unit of currency of the Bitcoin system. A commonly used shorthand for this is “BTC” to refer to a price or amount (eg: “100 BTC”).
There are such things as [[physical bitcoins]], but ultimately, a bitcoin is just a number associated with a [[Address|Bitcoin Address]]. A physical bitcoin is simply an object, such as a coin, with the number carefully embedded inside. See also an [[Introduction|easy intro]] to bitcoin.

=== How can I get bitcoins? ===

There are a variety of ways to acquire bitcoins:

* Accept bitcoins as payment for goods or services.
* There are several services where you can [[buying bitcoins|trade them]] for traditional currency.
* Find someone to trade cash for bitcoins in-person through a [https://en.bitcoin.it/wiki/Category:Directories local directory].
* Participate in a [[Pooled mining|mining pool]].
* If you have a lot of mining hardware, you can solo mine and attempt to create a new [[block]] (currently yields 50 bitcoins).

===Does Bitcoin guarantee an influx of free money?===

Since Bitcoin is a new technology, what it is and how it works may be initially unclear. Bitcoin is sometimes presented as being one of three things:
<ol style="list-style-type: upper-alpha;">
<li>Some sort of online 'get-rich-quick' scam.</li>
<li>A loophole in the market economy, the installation of which guarantees a steady influx of cash.</li>
<li>A sure investment that will almost certainly yield a profit.</li>
</ol>
In fact, none of the above are true. Let's look at them independently.

;Is Bitcoin a 'get-rich-quick' scheme?
:If you've spent much time on the Internet, you've probably seen ads for many 'get-rich-quick' schemes. These ads usually promise huge profits for a small amounts of easy work. Such schemes are usually pyramid/matrix-style schemes that make money from their own employees and offer nothing of any real value. Most convince one to buy packages that will make them earn hundreds a day, which in fact have the buyer distribute more such ads, and make minute profits.

:Bitcoin is in no way similar to these schemes. Bitcoin doesn't promise windfall profits. There is no way for the developers to make money from your involvement or to take money from you. That bitcoins are nearly impossible to acquire without the owner's consent represents one of its greatest strengths. Bitcoin is an experimental, virtual currency that may succeed or may fail. None of its developers expect to get rich off of it.

:A more detailed answer to this question can be found [http://bitcointalk.org/?topic=7815.0 here].

;Will I make money by installing the client?
:Most people who use Bitcoin don't earn anything by doing so, and the default client has no built-in way to earn Bitcoins. A small minority of people with dedicated, high-performance hardware do earn some Bitcoins by "''mining''" (generating new bitcoins, see [[#What is mining?|What is mining?]]) with special software, but joining Bitcoin shouldn't be construed as being the road to riches. Most Bitcoin users get involved because they find the project conceptually interesting and don't earn anything by doing so. This is also why you won't find much speculation about the political or economic repercussions of Bitcoin anywhere on this site: Bitcoin developers owe their dedication to the project's intellectual yieldings more than to those of a monetary nature. Bitcoin is still taking its first baby steps; it may go on to do great things but right now it only has something to offer those chasing conceptually interesting projects or bleeding edge technology.

;As an investment, is Bitcoin a sure thing?
:Bitcoin is a new and interesting electronic currency, the value of which is not backed by any single government or organization. Like other currencies, it is worth something partly because people are willing to trade it for goods and services. Its exchange rate fluctuates continuously, and sometimes wildly. It lacks wide acceptance and is vulnerable to manipulation by parties with modest funding. Security incidents such as website and account compromise may trigger major sell-offs. Other fluctuations can build into positive feedback loops cause much larger exchange rate fluctuations. Anyone who puts money into Bitcoin should take measures to reduce their risk and consider it as a high-risk currency. Later, as Bitcoin becomes better known and more widely accepted, it should stabilize, but for the time being it is unpredictable. Any investment in Bitcoin should be done carefully and with a clear plan to manage risk.

=== Can I buy bitcoins with Paypal? ===

It is possible to buy [[physical bitcoins]] with PayPal but it is otherwise difficult and/or expensive to do so, because of significant risk to the seller.

While it is possible to find an individual who wishes to sell Bitcoin to you via Paypal, (perhaps via [http://www.bitcoin-otc.com/ #bitcoin-otc] ) most exchanges do not allow funding through PayPal. This is due to repeated cases where someone pays for bitcoins with Paypal receives their bitcoins, and then fraudulently complains to Paypal that they never received their purchase. PayPal often sides with the fraudulent buyer in this case which means any seller would need to cover that risk with higher fees or refuse to accept PayPal altogether.

Buying Bitcoins from individuals with this method is still possible, but requires the seller to have some trust that the buyer will not file a claim with PayPal to reverse the payment.

=== Where can I find a forum to discuss Bitcoin? ===

Please visit the [[Bitcoin:Community_portal#Bitcoin_Community_Forums_on_various_platforms|Community Portal]] for links to Bitcoin-related forums.

=== How are new bitcoins created? ===

[[File:total_bitcoins_over_time_graph.png|thumb|Number of bitcoins over time, assuming a perfect 10-minute interval.]]
New bitcoins are generated by the network through the process of "[[#What is mining?|''mining'']]". In a process that is similar to a continuous lottery, mining nodes on the network are awarded bitcoins each time they find the solution to a certain mathematical problem (and thereby create a new [[block]]). Creating a block is a [[proof of work]] with a difficulty that varies with the overall strength of the network. The reward for solving a block is [[Controlled Currency Supply|automatically adjusted]] so that in roughly the first four years of operation of the Bitcoin network, {{formatnum:10500000}} BTC will be created. This amount is halved each four years, so it will be {{formatnum:5250000}} over years 4-8, {{formatnum:2625000}} over years 8-12, and so on. Thus the total number of bitcoins in existence will not exceed {{formatnum:21000000}}. See [[Controlled Currency Supply]].

Blocks are [[Mining|mined]] every 10 minutes, on average and for the first four years ({{formatnum:210000}} blocks) each block includes 50 new bitcoins. As the amount of processing power directed at mining changes, the difficulty of creating new bitcoins changes. This difficulty factor is calculated every 2016 blocks and is based upon the time taken to generate the previous 2016 blocks. See [[Mining]].

=== What's the current total number of Bitcoins in existence? ===

[http://blockexplorer.com/q/totalbc Current count]. Also see [https://blockchain.info/charts/total-bitcoins Total Bitcoins in circulation chart]

The number of blocks times the coin value of a block is the number of coins in existence. The coin value of a block is 50 BTC for each of the first 210,000 blocks, 25 BTC for the next 210,000 blocks, then 12.5 BTC, 6.25 BTC and so on.

=== How divisible are Bitcoins? ===

A bitcoin can be divided down to 8 decimal places. Therefore, 0.00000001 BTC is the smallest amount that can be handled in a transaction. If necessary, the protocol and related software can be modified to handle even smaller amounts.

=== What do I call the various denominations of Bitcoins? ===

There is a lot of discussion about the naming of these fractions of Bitcoins. The leading candidates are:

* 1 BTC = 1 Bitcoin
* 0.01 BTC = 1 cBTC = 1 Centi-Bitcoin (also referred to as Bitcent)
* 0.001 BTC = 1 mBTC = 1 Milli-Bitcoin (also referred to as mbit (pronounced em-bit) or millibit or even bitmill)
* 0.000 001 BTC = 1 μBTC = 1 Micro-Bitcoin (also referred to as ubit (pronounced yu-bit) or microbit)

The above follows the accepted international SI prefixes for hundredths, thousandths, and millionths. There are many arguments against the special case of 0.01 BTC since it is unlikely to represent anything meaningful as the Bitcoin economy grows (it certainly won't be the equivalent of 0.01 USD, GBP or EUR). Equally, the inclusion of existing national currency denominations such as "cent", "nickel", "dime", "pence", "pound", "kopek" and so on are to be discouraged. This is a worldwide currency.

One exception is the "satoshi" which is smallest denomination currently possible

* 0.000 000 01 BTC = 1 Satoshi (pronounced sa-toh-shee)

which is so named in honour of Satoshi Nakamoto the pseudonym of the inventor of Bitcoin.

For an overview of all defined units of Bitcoin (including less common and niche units), see [[Units]].

Further discussion on this topic can be found on the forums here:

* [http://forum.bitcoin.org/index.php?topic=14438.msg195287#msg195287 We need names]
* [http://forum.bitcoin.org/index.php?topic=8282.0 What to call 0.001 BTC]

=== How does the halving work when the number gets really small? ===

Eventually the reward will go from 0.00000001 BTC to zero and no more bitcoins will be created.

The block reward calculation is done as a right bitwise shift of a 64-bit signed integer, which means it is divided by two and rounded down. The integer is equal to the value in BTC * 100,000,000 since internally in the reference client software, all Bitcoin balances and values are stored as unsigned integers.

With an initial block reward of 50 BTC, it will take many 4-year periods for the block reward to reach zero.

=== How long will it take to generate all the coins? ===

The last block that will generate coins will be block #6,929,999 which should be generated at or near the year 2140. The total number of coins in circulation will then remain static at 20,999,999.9769 BTC.

Even if the allowed precision is expanded from the current 8 decimals, the total BTC in circulation will always be slightly below 21 million (assuming everything else stays the same). For example, with 16 decimals of precision, the end total would be 20,999,999.999999999496 BTC.

=== If no more coins are going to be generated, will more blocks be created? ===

Absolutely! Even before the creation of coins ends, the use of [[transaction fee|transaction fees]] will likely make creating new blocks more valuable from the fees than the new coins being created. When coin generation ends, these fees will sustain the ability to use bitcoins and the Bitcoin network. There is no practical limit on the number of blocks that will be mined in the future.

=== But if no more coins are generated, what happens when Bitcoins are lost? Won't that be a problem? ===

Because of the law of supply and demand, when fewer bitcoins are available the ones that are left will be in higher demand, and therefore will have a higher value. So, as Bitcoins are lost, the remaining bitcoins will eventually increase in value to compensate. As the value of a bitcoin increases, the number of bitcoins required to purchase an item '''de'''creases. This is a [[Deflationary spiral|deflationary economic model]]. As the average transaction size reduces, transactions will probably be denominated in sub-units of a bitcoin such as millibitcoins ("Millies") or microbitcoins ("Mikes").

The Bitcoin protocol uses a base unit of one hundred-millionth of a Bitcoin ("a Satoshi"), but unused bits are available in the protocol fields that could be used to denote even smaller subdivisions.

=== If every transaction is broadcast via the network, does Bitcoin scale? ===
The Bitcoin protocol allows lightweight clients that can use Bitcoin without downloading the entire transaction history. As traffic grows and this becomes more critical, implementations of the concept will be developed. Full network nodes will at some point become a more specialized service.

With some modifications to the software, full Bitcoin nodes could easily keep up with both VISA and MasterCard combined, using only fairly modest hardware (a single high end server by todays standards). It is worth noting that the MasterCard network is structured somewhat like Bitcoin itself - as a peer to peer broadcast network.

Learn more about [[Scalability]].

==Economy==
=== Where does the value of Bitcoin stem from? What backs up Bitcoin? ===
Bitcoins have value because they are useful and because they are [[Controlled Currency Supply|scarce]]. As they are accepted by more merchants, their value will [http://en.wikipedia.org/wiki/Sticky_%28economics%29 stabilize]. See the [[Trade|list of Bitcoin-accepting sites]].

When we say that a currency is backed up by gold, we mean that there's a promise in place that you can exchange the currency for gold. Bitcoins, like dollars and euros, are not backed up by anything except the variety of merchants that accept them.

It's a common misconception that Bitcoins gain their value from the cost of electricity required to generate them. Cost doesn't equal value – hiring 1,000 men to shovel a big hole in the ground may be costly, but not valuable. Also, even though scarcity is a critical requirement for a useful currency, it alone doesn't make anything valuable. For example, your fingerprints are scarce, but that doesn't mean they have any exchange value.

=== Is Bitcoin a bubble? ===
Yes, in the same way as the euro and dollar are. They only have value in exchange and have no inherent value. If everyone suddenly stopped accepting your dollars, euros or bitcoins, the "bubble" would burst and their value would drop to zero. But that is unlikely to happen: even in Somalia, where the government collapsed 20 years ago, [http://en.wikipedia.org/wiki/Somali_shilling Somali shillings] are still accepted as payment.

=== Is Bitcoin a Ponzi scheme? ===
In a Ponzi Scheme, the founders persuade investors that they’ll profit. Bitcoin does not make such a guarantee. There is no central entity, just individuals building an economy.

A ponzi scheme is a zero sum game. Early adopters can only profit at the expense of late adopters. Bitcoin has possible win-win outcomes. Early adopters profit from the rise in value. Late adopters, and indeed, society as a whole, benefit from the usefulness of a stable, fast, inexpensive, and widely accepted p2p currency.

The fact that early adopters benefit more doesn't alone make anything a Ponzi scheme. All good investments in successful companies have this quality.

=== Doesn't Bitcoin unfairly benefit early adopters? ===
Early adopters have a large number of bitcoins now because they took a risk and invested resources in an unproven technology. By so doing, they have helped Bitcoin become what it is now and what it will be in the future (hopefully, a ubiquitous decentralized digital currency). It is only fair they will reap the benefits of their successful investment.

In any case, any bitcoin generated will probably change hands dozens of time as a medium of exchange, so the profit made from the initial distribution will be insignificant compared to the total commerce enabled by Bitcoin.

Since the pricing of Bitcoins has fallen greatly from its June 2011 peak, prices today are much more similar to those enjoyed by many early adopters. Those who are buying Bitcoins today likely believe that Bitcoin will grow significantly in the future. Setting aside the brief opportunity to have sold Bitcoins at the June 2011 peak enjoyed by few, the early-adopter window is arguably still open.

===Won't loss of wallets and the finite amount of Bitcoins create excessive deflation, destroying Bitcoin? ===
Worries about Bitcoin being destroyed by deflation are not entirely unfounded. Unlike most currencies, which experience inflation as their founding institutions create more and more units, Bitcoin will likely experience gradual deflation with the passage of time. Bitcoin is unique in that only a small amount of units will ever be produced (twenty-one million to be exact), this number has been known since the project's inception, and the units are created at a predicable rate.

Also, Bitcoin users are faced with a danger that doesn't threaten users of any other currency: if a Bitcoin user loses his wallet, his money is gone forever, unless he finds it again. And not just to him; it's gone completely out of circulation, rendered utterly inaccessible to anyone. As people will lose their wallets, the total number of Bitcoins will slowly decrease.

Therefore, Bitcoin seems to be faced with a unique problem. Whereas most currencies inflate over time, Bitcoin will mostly likely do the just the opposite. Time will see the irretrievable loss of an ever-increasing number of Bitcoins. An already small number will be permanently whittled down further and further. And as there become fewer and fewer Bitcoins, the laws of supply and demand suggest that their value will probably continually rise.

Thus Bitcoin is bound to once again stray into mysterious territory, because no one exactly knows what happens to a currency that grows continually more valuable. Economists generally agree that a low level of inflation is a good thing for a currency, but nobody is quite sure about what might happens to one that continually deflates. Although deflation could hardly be called a rare phenomenon, steady, constant deflation is unheard of. There may be a lot of speculation, no one has any hard data to back up their claims.

That being said, there is a mechanism in place to combat the obvious consequences. Extreme deflation would render most currencies highly impractical: if a single Canadian dollar could suddenly buy the holder a car, how would one go about buying bread or candy? Even pennies would fetch more than a person could carry. Bitcoin, however, offers a simple and stylish solution: infinite divisibility. Bitcoins can be divided up and trade into as small of pieces as one wants, so no matter how valuable Bitcoins become, one can trade them in practical quantities.

In fact, infinite divisibility should allow Bitcoins to function in cases of extreme wallet loss. Even if, in the far future, so many people have lost their wallets that only a single Bitcoin, or a fraction of one, remains, Bitcoin should continue to function just fine. No one can claim to be sure what is going to happen, but deflation may prove to present a smaller threat than many expect.

For more information, see the [[Deflationary spiral]] page.

=== What if someone bought up all the existing Bitcoins? ===
Bitcoin markets are competitive -- meaning the price of a bitcoin will rise or fall depending on supply and demand at certain price levels. Only a fraction of bitcoins issued to date are found on the exchange markets for sale. So even though technically a buyer with lots of money could buy all the bitcoins offered for sale, unless those holding the rest of the bitcoins offer them for sale as well, even the wealthiest, most determined buyer can't get at them.

Additionally, new currency continues to be issued daily and will continue to do so for decades though over time the rate at which they are issued declines to insignificant levels. Those who are mining aren't obligated to sell their bitcoins so not all bitcoins will make it to the markets even.

This situation doesn't suggest, however, that the markets aren't vulnerable to price manipulation. It doesn't take significant amounts of money to move the market price up or down and thus Bitcoin remains a volatile asset.

===What if someone creates a new block chain, or a new digital currency that renders Bitcoin obsolete?===

That the block chain cannot be easily forked represents one of the central security mechanisms of Bitcoin. Given the choice between two block chains, a Bitcoin miner always chooses the longer one - that is to say, the one with the more complex hash. Thusly, it ensures that each user can only spend their bitcoins once, and that no user gets ripped off.

As a consequence of the block chain structure, there may at any time be many different sub-branches, and the possibility always exists of a transaction being over-written by the longest branch, if it has been recorded in a shorter one. The older a transaction is though, the lower its chances of being over-written, and the higher of becoming permanent. Although the block chain prevents one from spending more Bitcoins than one has, it means that transactions can be accidentally nullified.

A new block chain would leave the network vulnerable to [[double-spending|double-spend]] attacks. However, the creation of a viable new chain presents considerable difficulty, and the possibility does not present much of a risk.

Bitcoin will always choose the longer Block Chain and determines the relative length of two branches by the complexities of their hashes. Since the hash of each new block is made from that of the block preceding it, to create a block with a more complex hash, one must be prepared to do more computation than has been done by the entire Bitcoin network from the fork point up to the newest of the blocks one is trying to supersede. Needless to say, such an undertaking would require a very large amount of processing power and since Bitcoin is continually growing and expanding, it will likely only require more with the passage of time.

A much more distinct and real threat to the Bitcoin use is the development of other, superior virtual currencies, which could supplant Bitcoin and render it obsolete and valueless.

A great deal of careful thought and ingenuity has gone into the development of Bitcoin, but it is the first of its breed, a prototype, and vulnerable to more highly-evolved competitors. At present, any threatening rivals have yet to rear its head; Bitcoin remains the first and foremost private virtual currency, but we can offer no guarantees that it will retain that position. It would certainly be in keeping with internet history for similar system built from the same principles to supersede and cast Bitcoin into obsolescence, after time had revealed its major shortcomings. Friendster and Myspace suffered similar fates at the hand of Facebook, Napster was ousted by Limeware, Bearshare and torrent applications, and Skype has all but crushed the last few disciples of the Microsoft Messenger army.

This may sound rather foreboding, so bear in mind that introduction of new and possibly better virtual currencies will not necessarily herald Bitcoin's demise. If Bitcoin establishes itself sufficiently firmly before the inception of the next generation of private, online currencies as to gain widespread acceptance and general stability, future currencies may pose little threat even if they can claim superior design.

==Sending and Receiving Payments==

=== Why do I have to wait 10 minutes before I can spend money I received? ===

10 minutes is the average time taken to find a block. It can be significantly more or less time than that depending on luck; 10 minutes is simply the average case.

You can see how long all other recent transactions have taken here: [http://bitcoinstats.org/ BitcoinStats.org].

[[Blocks]] (shown as "confirmations" in the GUI) are how the Bitcoin achieves consensus on who owns what. Once a block is found everyone agrees that you now own those coins, so you can spend them again. Until then it's possible that some network nodes believe otherwise, if somebody is attempting to defraud the system by reversing a transaction. The more confirmations a transaction has, the less risk there is of a reversal. Only 6 blocks or 1 hour is enough to make reversal computationally impractical. This is dramatically better than credit cards which can see chargebacks occur up to three months after the original transaction!

Ten minutes was specifically chosen by [[Satoshi]] as a tradeoff between propagation time of new blocks in large networks and the amount of work wasted due to chain splits. For a more technical explanation, see Satoshi's [http://www.bitcoin.org/bitcoin.pdf original technical paper].

[[File:TransactionConfirmationTimesExample.PNG]]

=== Do you have to wait until my transactions are confirmed in order to buy or sell things with Bitcoin? ===

YES, you do, IF the transaction is non-recourse. The Bitcoin reference software does not display transactions as confirmed until six blocks have passed (confirmations). As transactions are burred in the chain they become increasingly non-reversible but are very reversible before the first confirmation. Two to six confirmations are recommended for non-recourse situations depending on the value of the transactions involved.

When people ask this question they are usually thinking about applications like supermarkets. This generally is a recourse situation: if somebody tries to double-spend on a face-to-face transaction it might work a few times, but probabalistically speaking eventually one of the double-spends will get noticed, and the penalty for shoplifting charges in most localities is calibrated to be several times worse than the proceeds of a single shoplifting event.

Double-spends might be a concern for something like a snack machine in a low-traffic area with no nearby security cameras. Such a machine shouldn't honor 0-confirmation payments, and should instead use some other mechanism of clearing Bitcoin or validating transactions against reversal, see the wiki article [[Myths#Point_of_sale_with_bitcoins_isn.27t_possible_because_of_the_10_minute_wait_for_confirmation|here]] for alternatives.

When people ask this question they are usually thinking about applications that require immediate payment processing, like supermarkets or snack machines. Here is one way to reverse an unconfirmed payment:

A [[Double-spending#Finney_attack|Finney attack]], in which an attacker mines a block containing a movement of some coins back to themselves. Once they find a block solution, they quickly go to a merchant and make a purchase, then broadcast the block, thus taking back the coins. This attack is a risk primarily for goods that are dispatched immediately, like song downloads or currency trades. Because the attacker can't choose the time of the attack, it isn't a risk for merchants such as supermarkets where you can't choose exactly when to pay (due to queues, etc). The attack can fail if somebody else finds a block containing the purchasing transaction before you release your own block, therefore, merchants can reduce but not eliminate the risk by making purchasers wait some length of time that's less than a confirm.

Because pulling off this attack is not trivial, merchants who need to sell things automatically and instantly are most likely to just price the cost of reversal fraud in, or use insurance.

=== I was sent some bitcoins and they haven't arrived yet! Where are they? ===

Don't panic! There are a number of reasons why your bitcoins might not show up yet, and a number of ways to diagnose them.

The latest version of the Bitcoin-Qt client tells you how far it has yet to go in downloading the blockchain. Hover over the icon in the bottom right corner of the client to learn your client's status.

If it has not caught up then it's possible that your transaction hasn't been included in a block yet.

You can check pending transactions in the network by going [http://blockchain.info here] and then searching for your address. If the transaction is listed here then it's a matter of waiting until it gets included in a block before it will show in your client.

Bear in mind that if the transaction is based on a coin that was in a recent transaction then it could be considered a low priority transaction take longer to transfer if the transaction fee paid isn't high enough. Very low priority transactions with 0 fees might take hours or days to be included in a block.

=== Why does my Bitcoin address keep changing? ===

Whenever the address listed in "Your address" receives a transaction, Bitcoin replaces it with a new address. This is meant to encourage you to use a new address for every transaction, which enhances [[anonymity]]. All of your old addresses are still usable: you can see them in ''Settings -> Your Receiving Addresses''.

===How much will the transaction fee be?===

Some transactions might require a [[transaction fee]] for them to get confirmed in a timely manner. The transaction fee is processed by and received by the bitcoin miner. The most recent version of the Bitcoin client will estimate an appropriate fee when a fee might be required.

The fee is added to the payment amount. For example, if you are sending a 1.234 BTC payment and the client requires a 0.0005 BTC fee, then 1.2345 BTC will be subtracted from the wallet balance for the entire transaction and the address for where the payment was sent will receive a payment of 1.234 BTC.

In cases where a fee is required it is required because your transaction objectively looks like a denial of service attack to the bitcoin system, either due to it being burdensome to transmit or it recycles bitcoins you recently received. The wallet software attempts to avoid generating burdensome transactions, but it isn't always able if the funds in your wallet are new or are composed of many very tiny payments.

Because the fee is related to the amount of data that makes up the transaction and not to the amount of bitcoins being sent, the fee may seem extremely low (0.0005 BTC for a 1,000 BTC transfer) or unfairly high (0.004 BTC for a 0.02 BTC payment, or about 20%). If you are receiving tiny amounts (e.g., as small payments from a mining pool) then fees when sending will be higher than if your activity follows a more normal consumer or business transaction pattern. As of bitcoin 0.5.3 the required fee it will ask for will not be higher than 0.05 BTC, though for most users there is usually no required fee at all and 0.0005 is the most common when one is required.

=== What happens when someone sends me a bitcoin but my computer is powered off? ===

Bitcoins aren't actually "sent" to your wallet, the software only uses that term so that we can use the currency without having to learn new concepts. Your wallet is only needed when you wish to spend coins that you've received.

The coins that were sent to you when the client was not running will later appear as if they were received in your wallet when you later launch the client. It will download blocks and catch up with any transactions it didn't already have.

=== How long does "synchronizing" take when the Bitcoin client is first installed? What's it doing? ===

The popular Bitcoin client software from bitcoin.org implements a "full" Bitcoin node: It can carry out all the duties of the Bitcoin P2P system, it isn't simply a "client". One of the principles behind the operation of full Bitcoin nodes is that they don't assume that the other participants have followed the rules of the Bitcoin system. During synchronization, the software is processing historical Bitcoin transactions and making sure for itself that all of the rules of the system have been correctly followed.

In normal operation, after synchronizing, the software should use a hardly noticeable amount of IO, CPU, or network capacity.

The initial validation is very disk-IO-intensive, so the amount of time to synchronize depends on your disk speed and, to a lesser extent, your CPU speed. It can take anywhere from a few hours to a day or so. You can use the software while this process is going on, but you may not see recent payments to you until the synchronization has caught up to the point where those transactions happened.

If this is too long for you, you can download a pre-synchronized blockchain from [http://eu1.bitcoincharts.com/blockchain/ http://eu1.bitcoincharts.com/blockchain/]. Alternatively, you can try an alternative "lite" client such as Multibit or a super-light client like electrum, though these clients have somewhat weaker security, are less mature, and don't contribute to the health of the P2P network.

==Networking==
=== Do I need to configure my firewall to run Bitcoin? ===

Bitcoin will connect to other nodes, usually on TCP port 8333. You will need to allow outgoing TCP connections to port 8333 if you want to allow your Bitcoin client to connect to many nodes. [[Testnet]] uses TCP port 18333 instead of 8333.

If you want to restrict your firewall rules to a few IPs, you can find stable nodes in the [[Fallback Nodes|fallback nodes list]].

=== How does the peer finding mechanism work? ===

Bitcoin finds peers primarily by forwarding peer announcements within its own network and each node saves a database of peers that it's aware of, for future use. In order to bootstrap this process Bitcoin needs a list of initial peers, these can be provided manually but normally it obtains them by querying a set of DNS domain names which have automatically updated lists, if that doesn't work it falls back to a build-in list which is updated from time to time in new versions of the software. There is also an IRC based mechanism but it is disabled by default.

==Mining==
===What is mining?===
[[Mining]] is the process of spending computation power to secure Bitcoin transactions against reversal and introducing new Bitcoins to the system.

Technically speaking, mining is the calculation of a [[hash]] of the a block header, which includes among other things a reference to the previous block, a hash of a set of transactions and a [[nonce]]. If the hash value is found to be less than the current [[target]] (which is inversely proportional to the [[difficulty]]), a new block is formed and the miner gets the newly generated Bitcoins (50 per block at current levels). If the hash is not less than the current target, a new nonce is tried, and a new hash is calculated. This is done millions of times per second by each miner.

===Is mining used for some useful computation?===
The computations done when mining are internal to Bitcoin and not related to any other distributed computing projects. They serve the purpose of securing the Bitcoin network, which is useful.

===Is it not a waste of energy?===
Spending energy on creating and securing a free monetary system is hardly a waste. Also, services necessary for the operation of currently widespread monetary systems, such as banks and credit card companies, also spend energy, arguably more than Bitcoin would.

===Why don't we use calculations that are also useful for some other purpose?===
To provide security for the Bitcoin network, the calculations involved need to have some very specific features. These features are incompatible with leveraging the computation for other purposes.

===How can we stop miners from creating zero transaction blocks?===
The incentive for miners to include transactions is in the fees that come along with them. If we were to implement some minimum number of transactions per block it would be trivial for a miner to create and include transactions merely to surpass that threshold. As the network matures, the block reward drops, and miners become more dependent on transactions fees to pay their costs, the problem of zero transaction blocks should diminish over time.

===How does the proof-of-work system help secure Bitcoin?===
To give a general idea of the mining process, imagine this setup:

payload = <some data related to things happening on the Bitcoin network>
nonce = 1
hash = [http://en.wikipedia.org/wiki/SHA2 SHA2]( [http://en.wikipedia.org/wiki/SHA2 SHA2]( payload + nonce ) )

The work performed by a miner consists of repeatedly increasing "nonce" until
the hash function yields a value, that has the rare property of being below a certain
target threshold. (In other words: The hash "starts with a certain number of zeroes",
if you display it in the fixed-length representation, that is typically used.)

As can be seen, the mining process doesn't compute anything special. It merely
tries to find a number (also referred to as nonce) which - in combination with the payload -
results in a hash with special properties.

The advantage of using such a mechanism consists of the fact, that it is very easy to check a result: Given the payload and a specific nonce, only a single call of the hashing function is needed to verify that the hash has the required properties. Since there is no known way to find these hashes other than brute force, this can be used as a "proof of work" that someone invested a lot of computing power to find the correct nonce for this payload.

This feature is then used in the Bitcoin network to secure various aspects. An attacker
that wants to introduce malicious payload data into the network, will need to do the
required proof of work before it will be accepted. And as long as honest miners have more
computing power, they can always outpace an attacker.

Also see [http://en.wikipedia.org/wiki/SHA2 SHA2] and [http://en.wikipedia.org/wiki/Proof-of-work_system Proof-of-work system] on Wikipedia.

===Why was the "Generate coin" option of the client software removed?===

In the early days of Bitcoin, it was easy for anyone to find new blocks using standard CPUs. As more and more people started mining, the [[difficulty]] of finding new blocks has greatly increased to the point where the average time for a CPU to find a single block can be many years. The only cost-effective method of [[Mining|mining]] is using a high-end graphics card with special software (see also [[Why a GPU mines faster than a CPU]]) and/or joining a [[Bitcoin Pool|mining pool]]. Since solo CPU mining is essentially useless, it was removed from the GUI of the Bitcoin software.

==Security==

===Could miners collude to give themselves money or to fundamentally change the nature of Bitcoin?===

There are two questions in here. Let's look at them separately.

;Could miners gang up and give themselves money?

Mining itself is the process of creating new blocks in the block chain. Each block contains a list of all the transactions that have taken place across the entire Bitcoin network since the last block was created, as well as a hash of the previous block. New blocks are 'mined', or rather, generated, by Bitcoin clients correctly guessing sequences of characters in codes called 'hashes,' which are created using information from previous blocks. Bitcoin users may download specialized 'mining' software, which allows them to dedicate some amount of their processing power – however large or small – to guessing at strings within the hash of the previous block. Whoever makes the right guess first, thus creating a new block, receives a reward in Bitcoins.

The block chain is one of the two structures that makes Bitcoin secure, the other being the public-key encryption system on which Bitcoin trade is based. The block chain assures that not only is every single transaction that ever takes place recorded, but that every single transaction is recorded on the computer of anyone who chooses to store the relevant information. Many, many users have complete records of every transaction in Bitcoins history readily available to them at any point, and anyone who wants in the information can obtain it with ease. These things make Bitcoin very hard to fool.

The Bitcoin network takes considerable processing power to run, and since those with the most processing power can make the most guesses, those who put the most power toward to sustaining the network earn the most currency. Each correct guess yields, at present, fifty Bitcoins, and as Bitcoins are presently worth something (although the value still fluctuates) every miner who earns any number of Bitcoins makes money. Some miners pull in Bitcoins on their own; and some also join or form pools wherein all who contribute earn a share of the profits.

Therefore, first answer is a vehement “yes” – no only can miners collude to get more money, Bitcoin is designed to encourage them to do so. Bitcoin pools are communal affairs, and there is nothing dishonest or underhanded about them.

Of course, the real question is:

;Can they do so in ways not sanction by Bitcoin developers? Is there any way to rip off the network and make loads of money dishonestly?

Bitcoin isn't infallible. It can be cheated, but doing so is extremely difficult. Bitcoin was designed to evade some of the central problems with modern currencies – namely, that their trustworthiness hinges upon that of people who might not have users' best interests in mind. Every currency in the world (other than Bitcoin) is controlled by large institutions who keep track of what's done with done with it, and who can manipulate its value. And every other currency has value because people trust the institutions that control them.

Bitcoin doesn't ask that its users trust any institution. Its security is based on the cryptography that is an integral part of its structure, and that is readily available for any and all to see. Instead of one entity keeping track of transactions, the entire network does, so Bitcoins are astoundingly difficult to steal, or double-spend. Bitcoins are created in a regular and predictable fashion, and by many different users, so no one can decide to make a whole lot more and lessen their value. In short, Bitcoin is designed to be inflation-proof, double-spend-proof and completely distributed.

Nonetheless, there are a few ways that one can acquire Bitcoins dishonestly. Firstly, one can steal private keys. Key theft isn't something that Bitcoin security has been designed to prevent: it's up to users to keep theirs safe. But the cryptography is designed so that it is completely impossible to deduce someone's private from their public one. As long as you keep your private key to yourself, you don't have much to worry about. Furthermore, one could theoretically create a new block chain, but due to the way in which the block chain is constructed, this would be extremely difficult and require massive amounts of processing power. A full explanation of the difficulties involved can be found in the [[block chain]] article.

Bitcoin can be ripped off – but doing so would be extremely hard and require considerable expertise and a staggering amount of processing power. And it's only going to get harder with time. Bitcoin isn't impenetrable, but it's close enough to put any real worries in the peripherals.

;Could miners fundamentally change the nature of Bitcoin?

Once again, almost certainly not.

Bitcoin is a distributed network, so any changes implemented to the system must be accepted by all users. Someone trying to change the way Bitcoins are generated would have to convince every user to download and use their software – so the only changes that would go through are those that would be equally benefit all users.

And thus, it is more or less impossible for anyone to change the function of Bitcoin to their advantage. If users don't like the changes, they won't adopt them, whereas if users do like them, then these will help everyone equally. Of course, one can conceive of a situation where someone manages to get a change pushed through that provides them with an advantage that no one notices, but given that Bitcoin is structurally relatively simple, it is unlikely that any major changes will go through without someone noticing first.

The fact that such changes are so difficult to make testifies to the fully distributed nature of Bitcoin. Any centrally controlled currency can be modified by its central agency without the consent of its adherents. Bitcoin has no central authority, so it changes only at the behest of the whole community. Bitcoins development represents a kind of collective evolution; the first of its kind among currencies.

==Help==
===I'd like to learn more. Where can I get help?===

* Read the [[Introduction|introduction to bitcoin]]
* See the videos, podcasts, and blog posts from the [[Press]]
* Read and post on the [[Bitcoin:Community_portal#Bitcoin_Community_Forums|forums]]
* Chat on one of the [[Bitcoin:Community_portal#IRC_Chat|Bitcoin IRC]] channels
* Listen to [http://omegataupodcast.net/2011/03/59-bitcoin-a-digital-decentralized-currency/ this podcast], which goes into the details of how bitcoin works
* Ask questions on the [http://bitcoin.stackexchange.com Bitcoin Stack Exchange]

==See Also==

* [[Man page]]
* [[Introduction]]

[[de:FAQ]]
[[zh-cn:FAQ]]
[[fr:FAQ]]
[[ru:FAQ]]

[[Category:Technical]]
[[Category:Vocabulary]]

Help:FAQ

2012-10-25T15:36:34Z

Jepo: /* Does Bitcoin guarantee an influx of free money? */

Here you will find answers to the most commonly asked questions.

== General ==
=== What are bitcoins? ===
Bitcoins are the unit of currency of the Bitcoin system. A commonly used shorthand for this is “BTC” to refer to a price or amount (eg: “100 BTC”).
There are such things as [[physical bitcoins]], but ultimately, a bitcoin is just a number associated with a [[Address|Bitcoin Address]]. A physical bitcoin is simply an object, such as a coin, with the number carefully embedded inside. See also an [[Introduction|easy intro]] to bitcoin.

=== How can I get bitcoins? ===

There are a variety of ways to acquire bitcoins:

* Accept bitcoins as payment for goods or services.
* There are several services where you can [[buying bitcoins|trade them]] for traditional currency.
* Find someone to trade cash for bitcoins in-person through a [https://en.bitcoin.it/wiki/Category:Directories local directory].
* Participate in a [[Pooled mining|mining pool]].
* If you have a lot of mining hardware, you can solo mine and attempt to create a new [[block]] (currently yields 50 bitcoins).

===Does Bitcoin guarantee an influx of free money?===

Since Bitcoin is a new technology, what it is and how it works may be initially unclear. Bitcoin is sometimes presented as being one of three things:
<ol style="list-style-type: upper-alpha;">
<li>Some sort of online 'get-rich-quick' scam.</li>
<li>A loophole in the market economy, the installation of which guarantees a steady influx of cash.</li>
<li>A sure investment that will almost certainly yield a profit.</li>
</ol>
In fact, none of the above are true. Let's look at them independently.

;Is Bitcoin a 'get-rich-quick' scheme?
:If you've spent much time on the Internet, you've probably seen ads for many 'get-rich-quick' schemes. These ads usually promise huge profits for a small amounts of easy work. Such schemes are usually pyramid/matrix-style schemes that make money from their own employees and offer nothing of any real value. Most convince one to buy packages that will make them earn hundreds a day, which in fact have the buyer distribute more such ads, and make minute profits.

:Bitcoin is in no way similar to these schemes. Bitcoin doesn't promise windfall profits. There is no way for the developers to make money from your involvement or to take money from you. That bitcoins are nearly impossible to acquire without the owner's consent represents one of its greatest strengths. Bitcoin is an experimental, virtual currency that may succeed or may fail. None of its developers expect to get rich off of it.

:A more detailed answer to this question can be found [http://bitcointalk.org/?topic=7815.0 here].

;Will I make money by installing the client?
:Most people who use Bitcoin don't earn anything by doing so, and the default client has no built-in way to earn Bitcoins. A small minority of people with dedicated, high-performance hardware do earn some Bitcoins by "''mining''" (generating new bitcoins, see [[#What is mining?|What is mining?]]) with special software, but joining Bitcoin shouldn't be construed as being the road to riches. Most Bitcoin users get involved because they find the project conceptually interesting and don't earn anything by doing so. This is also why you won't find much speculation about the political or economic repercussions of Bitcoin anywhere on this site: Bitcoin developers owe their dedication to the project's intellectual yieldings more than to those of a monetary nature. Bitcoin is still taking its first baby steps; it may go on to do great things but right now it only has something to offer those chasing conceptually interesting projects or bleeding edge technology.

;As an investment, is Bitcoin a sure thing?
:Bitcoin is a new and interesting electronic currency, the value of which is not backed by any single government or organization. Like other currencies, it is worth something partly because people are willing to trade it for goods and services. Its exchange rate fluctuates continuously, and sometimes wildly. It lacks wide acceptance and is vulnerable to manipulation by parties with modest funding. Security incidents such as website and account compromise may trigger major sell-offs. Other fluctuations can build into positive feedback loops cause much larger exchange rate fluctuations. Anyone who puts money into Bitcoin should take measures to reduce their risk and consider it as a high-risk currency. Later, as Bitcoin becomes better known and more widely accepted, it should stabilize, but for the time being it is unpredictable. Any investment in Bitcoin should be done carefully and with a clear plan to manage risk.

=== Can I buy bitcoins with Paypal? ===

It is possible to buy [[physical bitcoins]] with PayPal but it is otherwise difficult and/or expensive to do so, because of significant risk to the seller.

While it is possible to find an individual who wishes to sell Bitcoin to you via Paypal, (perhaps via [http://www.bitcoin-otc.com/ #bitcoin-otc] ) most exchanges do not allow funding through PayPal. This is due to repeated cases where someone pays for bitcoins with Paypal receives their bitcoins, and then fraudulently complains to Paypal that they never received their purchase. PayPal often sides with the fraudulent buyer in this case which means any seller would need to cover that risk with higher fees or refuse to accept PayPal altogether.

Buying Bitcoins from individuals with this method is still possible, but requires the seller to have some trust that the buyer will not file a claim with PayPal to reverse the payment.

=== Where can I find a forum to discuss Bitcoin? ===

Please visit the [[Bitcoin:Community_portal#Bitcoin_Community_Forums_on_various_platforms|Community Portal]] for links to Bitcoin-related forums.

=== How are new bitcoins created? ===

[[File:total_bitcoins_over_time_graph.png|thumb|Number of bitcoins over time, assuming a perfect 10-minute interval.]]
New bitcoins are generated by the network through the process of mining. In a process that is similar to a continuous lottery, mining nodes on the network are awarded bitcoins each time they find the solution to a certain mathematical problem (and thereby create a new [[block]]). Creating a block is a [[proof of work]] with a difficulty that varies with the overall strength of the network. The reward for solving a block is [[Controlled Currency Supply|automatically adjusted]] so that in roughly the first four years of operation of the Bitcoin network, 10,500,000 BTC will be created. This amount is halved each four years, so it will be 5,250,000 over years 4-8, 2,625,000 over years 8-12 and so on. Thus the total number of bitcoins in existence will not exceed 21,000,000. See [[Controlled Currency Supply]].

Blocks are [[Mining|mined]] every 10 minutes, on average and for the first four years (210,000 blocks) each block includes 50 new bitcoins. As the amount of processing power directed at mining changes, the difficulty of creating new bitcoins changes. This difficulty factor is calculated every 2016 blocks and is based upon the time taken to generate the previous 2016 blocks. See [[Mining]].

=== What's the current total number of Bitcoins in existence? ===

[http://blockexplorer.com/q/totalbc Current count]. Also see [https://blockchain.info/charts/total-bitcoins Total Bitcoins in circulation chart]

The number of blocks times the coin value of a block is the number of coins in existence. The coin value of a block is 50 BTC for each of the first 210,000 blocks, 25 BTC for the next 210,000 blocks, then 12.5 BTC, 6.25 BTC and so on.

=== How divisible are Bitcoins? ===

A bitcoin can be divided down to 8 decimal places. Therefore, 0.00000001 BTC is the smallest amount that can be handled in a transaction. If necessary, the protocol and related software can be modified to handle even smaller amounts.

=== What do I call the various denominations of Bitcoins? ===

There is a lot of discussion about the naming of these fractions of Bitcoins. The leading candidates are:

* 1 BTC = 1 Bitcoin
* 0.01 BTC = 1 cBTC = 1 Centi-Bitcoin (also referred to as Bitcent)
* 0.001 BTC = 1 mBTC = 1 Milli-Bitcoin (also referred to as mbit (pronounced em-bit) or millibit or even bitmill)
* 0.000 001 BTC = 1 μBTC = 1 Micro-Bitcoin (also referred to as ubit (pronounced yu-bit) or microbit)

The above follows the accepted international SI prefixes for hundredths, thousandths, and millionths. There are many arguments against the special case of 0.01 BTC since it is unlikely to represent anything meaningful as the Bitcoin economy grows (it certainly won't be the equivalent of 0.01 USD, GBP or EUR). Equally, the inclusion of existing national currency denominations such as "cent", "nickel", "dime", "pence", "pound", "kopek" and so on are to be discouraged. This is a worldwide currency.

One exception is the "satoshi" which is smallest denomination currently possible

* 0.000 000 01 BTC = 1 Satoshi (pronounced sa-toh-shee)

which is so named in honour of Satoshi Nakamoto the pseudonym of the inventor of Bitcoin.

For an overview of all defined units of Bitcoin (including less common and niche units), see [[Units]].

Further discussion on this topic can be found on the forums here:

* [http://forum.bitcoin.org/index.php?topic=14438.msg195287#msg195287 We need names]
* [http://forum.bitcoin.org/index.php?topic=8282.0 What to call 0.001 BTC]

=== How does the halving work when the number gets really small? ===

Eventually the reward will go from 0.00000001 BTC to zero and no more bitcoins will be created.

The block reward calculation is done as a right bitwise shift of a 64-bit signed integer, which means it is divided by two and rounded down. The integer is equal to the value in BTC * 100,000,000 since internally in the reference client software, all Bitcoin balances and values are stored as unsigned integers.

With an initial block reward of 50 BTC, it will take many 4-year periods for the block reward to reach zero.

=== How long will it take to generate all the coins? ===

The last block that will generate coins will be block #6,929,999 which should be generated at or near the year 2140. The total number of coins in circulation will then remain static at 20,999,999.9769 BTC.

Even if the allowed precision is expanded from the current 8 decimals, the total BTC in circulation will always be slightly below 21 million (assuming everything else stays the same). For example, with 16 decimals of precision, the end total would be 20,999,999.999999999496 BTC.

=== If no more coins are going to be generated, will more blocks be created? ===

Absolutely! Even before the creation of coins ends, the use of [[transaction fee|transaction fees]] will likely make creating new blocks more valuable from the fees than the new coins being created. When coin generation ends, these fees will sustain the ability to use bitcoins and the Bitcoin network. There is no practical limit on the number of blocks that will be mined in the future.

=== But if no more coins are generated, what happens when Bitcoins are lost? Won't that be a problem? ===

Because of the law of supply and demand, when fewer bitcoins are available the ones that are left will be in higher demand, and therefore will have a higher value. So, as Bitcoins are lost, the remaining bitcoins will eventually increase in value to compensate. As the value of a bitcoin increases, the number of bitcoins required to purchase an item '''de'''creases. This is a [[Deflationary spiral|deflationary economic model]]. As the average transaction size reduces, transactions will probably be denominated in sub-units of a bitcoin such as millibitcoins ("Millies") or microbitcoins ("Mikes").

The Bitcoin protocol uses a base unit of one hundred-millionth of a Bitcoin ("a Satoshi"), but unused bits are available in the protocol fields that could be used to denote even smaller subdivisions.

=== If every transaction is broadcast via the network, does Bitcoin scale? ===
The Bitcoin protocol allows lightweight clients that can use Bitcoin without downloading the entire transaction history. As traffic grows and this becomes more critical, implementations of the concept will be developed. Full network nodes will at some point become a more specialized service.

With some modifications to the software, full Bitcoin nodes could easily keep up with both VISA and MasterCard combined, using only fairly modest hardware (a single high end server by todays standards). It is worth noting that the MasterCard network is structured somewhat like Bitcoin itself - as a peer to peer broadcast network.

Learn more about [[Scalability]].

==Economy==
=== Where does the value of Bitcoin stem from? What backs up Bitcoin? ===
Bitcoins have value because they are useful and because they are [[Controlled Currency Supply|scarce]]. As they are accepted by more merchants, their value will [http://en.wikipedia.org/wiki/Sticky_%28economics%29 stabilize]. See the [[Trade|list of Bitcoin-accepting sites]].

When we say that a currency is backed up by gold, we mean that there's a promise in place that you can exchange the currency for gold. Bitcoins, like dollars and euros, are not backed up by anything except the variety of merchants that accept them.

It's a common misconception that Bitcoins gain their value from the cost of electricity required to generate them. Cost doesn't equal value – hiring 1,000 men to shovel a big hole in the ground may be costly, but not valuable. Also, even though scarcity is a critical requirement for a useful currency, it alone doesn't make anything valuable. For example, your fingerprints are scarce, but that doesn't mean they have any exchange value.

=== Is Bitcoin a bubble? ===
Yes, in the same way as the euro and dollar are. They only have value in exchange and have no inherent value. If everyone suddenly stopped accepting your dollars, euros or bitcoins, the "bubble" would burst and their value would drop to zero. But that is unlikely to happen: even in Somalia, where the government collapsed 20 years ago, [http://en.wikipedia.org/wiki/Somali_shilling Somali shillings] are still accepted as payment.

=== Is Bitcoin a Ponzi scheme? ===
In a Ponzi Scheme, the founders persuade investors that they’ll profit. Bitcoin does not make such a guarantee. There is no central entity, just individuals building an economy.

A ponzi scheme is a zero sum game. Early adopters can only profit at the expense of late adopters. Bitcoin has possible win-win outcomes. Early adopters profit from the rise in value. Late adopters, and indeed, society as a whole, benefit from the usefulness of a stable, fast, inexpensive, and widely accepted p2p currency.

The fact that early adopters benefit more doesn't alone make anything a Ponzi scheme. All good investments in successful companies have this quality.

=== Doesn't Bitcoin unfairly benefit early adopters? ===
Early adopters have a large number of bitcoins now because they took a risk and invested resources in an unproven technology. By so doing, they have helped Bitcoin become what it is now and what it will be in the future (hopefully, a ubiquitous decentralized digital currency). It is only fair they will reap the benefits of their successful investment.

In any case, any bitcoin generated will probably change hands dozens of time as a medium of exchange, so the profit made from the initial distribution will be insignificant compared to the total commerce enabled by Bitcoin.

Since the pricing of Bitcoins has fallen greatly from its June 2011 peak, prices today are much more similar to those enjoyed by many early adopters. Those who are buying Bitcoins today likely believe that Bitcoin will grow significantly in the future. Setting aside the brief opportunity to have sold Bitcoins at the June 2011 peak enjoyed by few, the early-adopter window is arguably still open.

===Won't loss of wallets and the finite amount of Bitcoins create excessive deflation, destroying Bitcoin? ===
Worries about Bitcoin being destroyed by deflation are not entirely unfounded. Unlike most currencies, which experience inflation as their founding institutions create more and more units, Bitcoin will likely experience gradual deflation with the passage of time. Bitcoin is unique in that only a small amount of units will ever be produced (twenty-one million to be exact), this number has been known since the project's inception, and the units are created at a predicable rate.

Also, Bitcoin users are faced with a danger that doesn't threaten users of any other currency: if a Bitcoin user loses his wallet, his money is gone forever, unless he finds it again. And not just to him; it's gone completely out of circulation, rendered utterly inaccessible to anyone. As people will lose their wallets, the total number of Bitcoins will slowly decrease.

Therefore, Bitcoin seems to be faced with a unique problem. Whereas most currencies inflate over time, Bitcoin will mostly likely do the just the opposite. Time will see the irretrievable loss of an ever-increasing number of Bitcoins. An already small number will be permanently whittled down further and further. And as there become fewer and fewer Bitcoins, the laws of supply and demand suggest that their value will probably continually rise.

Thus Bitcoin is bound to once again stray into mysterious territory, because no one exactly knows what happens to a currency that grows continually more valuable. Economists generally agree that a low level of inflation is a good thing for a currency, but nobody is quite sure about what might happens to one that continually deflates. Although deflation could hardly be called a rare phenomenon, steady, constant deflation is unheard of. There may be a lot of speculation, no one has any hard data to back up their claims.

That being said, there is a mechanism in place to combat the obvious consequences. Extreme deflation would render most currencies highly impractical: if a single Canadian dollar could suddenly buy the holder a car, how would one go about buying bread or candy? Even pennies would fetch more than a person could carry. Bitcoin, however, offers a simple and stylish solution: infinite divisibility. Bitcoins can be divided up and trade into as small of pieces as one wants, so no matter how valuable Bitcoins become, one can trade them in practical quantities.

In fact, infinite divisibility should allow Bitcoins to function in cases of extreme wallet loss. Even if, in the far future, so many people have lost their wallets that only a single Bitcoin, or a fraction of one, remains, Bitcoin should continue to function just fine. No one can claim to be sure what is going to happen, but deflation may prove to present a smaller threat than many expect.

For more information, see the [[Deflationary spiral]] page.

=== What if someone bought up all the existing Bitcoins? ===
Bitcoin markets are competitive -- meaning the price of a bitcoin will rise or fall depending on supply and demand at certain price levels. Only a fraction of bitcoins issued to date are found on the exchange markets for sale. So even though technically a buyer with lots of money could buy all the bitcoins offered for sale, unless those holding the rest of the bitcoins offer them for sale as well, even the wealthiest, most determined buyer can't get at them.

Additionally, new currency continues to be issued daily and will continue to do so for decades though over time the rate at which they are issued declines to insignificant levels. Those who are mining aren't obligated to sell their bitcoins so not all bitcoins will make it to the markets even.

This situation doesn't suggest, however, that the markets aren't vulnerable to price manipulation. It doesn't take significant amounts of money to move the market price up or down and thus Bitcoin remains a volatile asset.

===What if someone creates a new block chain, or a new digital currency that renders Bitcoin obsolete?===

That the block chain cannot be easily forked represents one of the central security mechanisms of Bitcoin. Given the choice between two block chains, a Bitcoin miner always chooses the longer one - that is to say, the one with the more complex hash. Thusly, it ensures that each user can only spend their bitcoins once, and that no user gets ripped off.

As a consequence of the block chain structure, there may at any time be many different sub-branches, and the possibility always exists of a transaction being over-written by the longest branch, if it has been recorded in a shorter one. The older a transaction is though, the lower its chances of being over-written, and the higher of becoming permanent. Although the block chain prevents one from spending more Bitcoins than one has, it means that transactions can be accidentally nullified.

A new block chain would leave the network vulnerable to [[double-spending|double-spend]] attacks. However, the creation of a viable new chain presents considerable difficulty, and the possibility does not present much of a risk.

Bitcoin will always choose the longer Block Chain and determines the relative length of two branches by the complexities of their hashes. Since the hash of each new block is made from that of the block preceding it, to create a block with a more complex hash, one must be prepared to do more computation than has been done by the entire Bitcoin network from the fork point up to the newest of the blocks one is trying to supersede. Needless to say, such an undertaking would require a very large amount of processing power and since Bitcoin is continually growing and expanding, it will likely only require more with the passage of time.

A much more distinct and real threat to the Bitcoin use is the development of other, superior virtual currencies, which could supplant Bitcoin and render it obsolete and valueless.

A great deal of careful thought and ingenuity has gone into the development of Bitcoin, but it is the first of its breed, a prototype, and vulnerable to more highly-evolved competitors. At present, any threatening rivals have yet to rear its head; Bitcoin remains the first and foremost private virtual currency, but we can offer no guarantees that it will retain that position. It would certainly be in keeping with internet history for similar system built from the same principles to supersede and cast Bitcoin into obsolescence, after time had revealed its major shortcomings. Friendster and Myspace suffered similar fates at the hand of Facebook, Napster was ousted by Limeware, Bearshare and torrent applications, and Skype has all but crushed the last few disciples of the Microsoft Messenger army.

This may sound rather foreboding, so bear in mind that introduction of new and possibly better virtual currencies will not necessarily herald Bitcoin's demise. If Bitcoin establishes itself sufficiently firmly before the inception of the next generation of private, online currencies as to gain widespread acceptance and general stability, future currencies may pose little threat even if they can claim superior design.

==Sending and Receiving Payments==

=== Why do I have to wait 10 minutes before I can spend money I received? ===

10 minutes is the average time taken to find a block. It can be significantly more or less time than that depending on luck; 10 minutes is simply the average case.

You can see how long all other recent transactions have taken here: [http://bitcoinstats.org/ BitcoinStats.org].

[[Blocks]] (shown as "confirmations" in the GUI) are how the Bitcoin achieves consensus on who owns what. Once a block is found everyone agrees that you now own those coins, so you can spend them again. Until then it's possible that some network nodes believe otherwise, if somebody is attempting to defraud the system by reversing a transaction. The more confirmations a transaction has, the less risk there is of a reversal. Only 6 blocks or 1 hour is enough to make reversal computationally impractical. This is dramatically better than credit cards which can see chargebacks occur up to three months after the original transaction!

Ten minutes was specifically chosen by [[Satoshi]] as a tradeoff between propagation time of new blocks in large networks and the amount of work wasted due to chain splits. For a more technical explanation, see Satoshi's [http://www.bitcoin.org/bitcoin.pdf original technical paper].

[[File:TransactionConfirmationTimesExample.PNG]]

=== Do you have to wait until my transactions are confirmed in order to buy or sell things with Bitcoin? ===

YES, you do, IF the transaction is non-recourse. The Bitcoin reference software does not display transactions as confirmed until six blocks have passed (confirmations). As transactions are burred in the chain they become increasingly non-reversible but are very reversible before the first confirmation. Two to six confirmations are recommended for non-recourse situations depending on the value of the transactions involved.

When people ask this question they are usually thinking about applications like supermarkets. This generally is a recourse situation: if somebody tries to double-spend on a face-to-face transaction it might work a few times, but probabalistically speaking eventually one of the double-spends will get noticed, and the penalty for shoplifting charges in most localities is calibrated to be several times worse than the proceeds of a single shoplifting event.

Double-spends might be a concern for something like a snack machine in a low-traffic area with no nearby security cameras. Such a machine shouldn't honor 0-confirmation payments, and should instead use some other mechanism of clearing Bitcoin or validating transactions against reversal, see the wiki article [[Myths#Point_of_sale_with_bitcoins_isn.27t_possible_because_of_the_10_minute_wait_for_confirmation|here]] for alternatives.

When people ask this question they are usually thinking about applications that require immediate payment processing, like supermarkets or snack machines. Here is one way to reverse an unconfirmed payment:

A [[Double-spending#Finney_attack|Finney attack]], in which an attacker mines a block containing a movement of some coins back to themselves. Once they find a block solution, they quickly go to a merchant and make a purchase, then broadcast the block, thus taking back the coins. This attack is a risk primarily for goods that are dispatched immediately, like song downloads or currency trades. Because the attacker can't choose the time of the attack, it isn't a risk for merchants such as supermarkets where you can't choose exactly when to pay (due to queues, etc). The attack can fail if somebody else finds a block containing the purchasing transaction before you release your own block, therefore, merchants can reduce but not eliminate the risk by making purchasers wait some length of time that's less than a confirm.

Because pulling off this attack is not trivial, merchants who need to sell things automatically and instantly are most likely to just price the cost of reversal fraud in, or use insurance.

=== I was sent some bitcoins and they haven't arrived yet! Where are they? ===

Don't panic! There are a number of reasons why your bitcoins might not show up yet, and a number of ways to diagnose them.

The latest version of the Bitcoin-Qt client tells you how far it has yet to go in downloading the blockchain. Hover over the icon in the bottom right corner of the client to learn your client's status.

If it has not caught up then it's possible that your transaction hasn't been included in a block yet.

You can check pending transactions in the network by going [http://blockchain.info here] and then searching for your address. If the transaction is listed here then it's a matter of waiting until it gets included in a block before it will show in your client.

Bear in mind that if the transaction is based on a coin that was in a recent transaction then it could be considered a low priority transaction take longer to transfer if the transaction fee paid isn't high enough. Very low priority transactions with 0 fees might take hours or days to be included in a block.

=== Why does my Bitcoin address keep changing? ===

Whenever the address listed in "Your address" receives a transaction, Bitcoin replaces it with a new address. This is meant to encourage you to use a new address for every transaction, which enhances [[anonymity]]. All of your old addresses are still usable: you can see them in ''Settings -> Your Receiving Addresses''.

===How much will the transaction fee be?===

Some transactions might require a [[transaction fee]] for them to get confirmed in a timely manner. The transaction fee is processed by and received by the bitcoin miner. The most recent version of the Bitcoin client will estimate an appropriate fee when a fee might be required.

The fee is added to the payment amount. For example, if you are sending a 1.234 BTC payment and the client requires a 0.0005 BTC fee, then 1.2345 BTC will be subtracted from the wallet balance for the entire transaction and the address for where the payment was sent will receive a payment of 1.234 BTC.

In cases where a fee is required it is required because your transaction objectively looks like a denial of service attack to the bitcoin system, either due to it being burdensome to transmit or it recycles bitcoins you recently received. The wallet software attempts to avoid generating burdensome transactions, but it isn't always able if the funds in your wallet are new or are composed of many very tiny payments.

Because the fee is related to the amount of data that makes up the transaction and not to the amount of bitcoins being sent, the fee may seem extremely low (0.0005 BTC for a 1,000 BTC transfer) or unfairly high (0.004 BTC for a 0.02 BTC payment, or about 20%). If you are receiving tiny amounts (e.g., as small payments from a mining pool) then fees when sending will be higher than if your activity follows a more normal consumer or business transaction pattern. As of bitcoin 0.5.3 the required fee it will ask for will not be higher than 0.05 BTC, though for most users there is usually no required fee at all and 0.0005 is the most common when one is required.

=== What happens when someone sends me a bitcoin but my computer is powered off? ===

Bitcoins aren't actually "sent" to your wallet, the software only uses that term so that we can use the currency without having to learn new concepts. Your wallet is only needed when you wish to spend coins that you've received.

The coins that were sent to you when the client was not running will later appear as if they were received in your wallet when you later launch the client. It will download blocks and catch up with any transactions it didn't already have.

=== How long does "synchronizing" take when the Bitcoin client is first installed? What's it doing? ===

The popular Bitcoin client software from bitcoin.org implements a "full" Bitcoin node: It can carry out all the duties of the Bitcoin P2P system, it isn't simply a "client". One of the principles behind the operation of full Bitcoin nodes is that they don't assume that the other participants have followed the rules of the Bitcoin system. During synchronization, the software is processing historical Bitcoin transactions and making sure for itself that all of the rules of the system have been correctly followed.

In normal operation, after synchronizing, the software should use a hardly noticeable amount of IO, CPU, or network capacity.

The initial validation is very disk-IO-intensive, so the amount of time to synchronize depends on your disk speed and, to a lesser extent, your CPU speed. It can take anywhere from a few hours to a day or so. You can use the software while this process is going on, but you may not see recent payments to you until the synchronization has caught up to the point where those transactions happened.

If this is too long for you, you can download a pre-synchronized blockchain from [http://eu1.bitcoincharts.com/blockchain/ http://eu1.bitcoincharts.com/blockchain/]. Alternatively, you can try an alternative "lite" client such as Multibit or a super-light client like electrum, though these clients have somewhat weaker security, are less mature, and don't contribute to the health of the P2P network.

==Networking==
=== Do I need to configure my firewall to run Bitcoin? ===

Bitcoin will connect to other nodes, usually on TCP port 8333. You will need to allow outgoing TCP connections to port 8333 if you want to allow your Bitcoin client to connect to many nodes. [[Testnet]] uses TCP port 18333 instead of 8333.

If you want to restrict your firewall rules to a few IPs, you can find stable nodes in the [[Fallback Nodes|fallback nodes list]].

=== How does the peer finding mechanism work? ===

Bitcoin finds peers primarily by forwarding peer announcements within its own network and each node saves a database of peers that it's aware of, for future use. In order to bootstrap this process Bitcoin needs a list of initial peers, these can be provided manually but normally it obtains them by querying a set of DNS domain names which have automatically updated lists, if that doesn't work it falls back to a build-in list which is updated from time to time in new versions of the software. There is also an IRC based mechanism but it is disabled by default.

==Mining==
===What is mining?===
[[Mining]] is the process of spending computation power to secure Bitcoin transactions against reversal and introducing new Bitcoins to the system.

Technically speaking, mining is the calculation of a [[hash]] of the a block header, which includes among other things a reference to the previous block, a hash of a set of transactions and a [[nonce]]. If the hash value is found to be less than the current [[target]] (which is inversely proportional to the [[difficulty]]), a new block is formed and the miner gets the newly generated Bitcoins (50 per block at current levels). If the hash is not less than the current target, a new nonce is tried, and a new hash is calculated. This is done millions of times per second by each miner.

===Is mining used for some useful computation?===
The computations done when mining are internal to Bitcoin and not related to any other distributed computing projects. They serve the purpose of securing the Bitcoin network, which is useful.

===Is it not a waste of energy?===
Spending energy on creating and securing a free monetary system is hardly a waste. Also, services necessary for the operation of currently widespread monetary systems, such as banks and credit card companies, also spend energy, arguably more than Bitcoin would.

===Why don't we use calculations that are also useful for some other purpose?===
To provide security for the Bitcoin network, the calculations involved need to have some very specific features. These features are incompatible with leveraging the computation for other purposes.

===How can we stop miners from creating zero transaction blocks?===
The incentive for miners to include transactions is in the fees that come along with them. If we were to implement some minimum number of transactions per block it would be trivial for a miner to create and include transactions merely to surpass that threshold. As the network matures, the block reward drops, and miners become more dependent on transactions fees to pay their costs, the problem of zero transaction blocks should diminish over time.

===How does the proof-of-work system help secure Bitcoin?===
To give a general idea of the mining process, imagine this setup:

payload = <some data related to things happening on the Bitcoin network>
nonce = 1
hash = [http://en.wikipedia.org/wiki/SHA2 SHA2]( [http://en.wikipedia.org/wiki/SHA2 SHA2]( payload + nonce ) )

The work performed by a miner consists of repeatedly increasing "nonce" until
the hash function yields a value, that has the rare property of being below a certain
target threshold. (In other words: The hash "starts with a certain number of zeroes",
if you display it in the fixed-length representation, that is typically used.)

As can be seen, the mining process doesn't compute anything special. It merely
tries to find a number (also referred to as nonce) which - in combination with the payload -
results in a hash with special properties.

The advantage of using such a mechanism consists of the fact, that it is very easy to check a result: Given the payload and a specific nonce, only a single call of the hashing function is needed to verify that the hash has the required properties. Since there is no known way to find these hashes other than brute force, this can be used as a "proof of work" that someone invested a lot of computing power to find the correct nonce for this payload.

This feature is then used in the Bitcoin network to secure various aspects. An attacker
that wants to introduce malicious payload data into the network, will need to do the
required proof of work before it will be accepted. And as long as honest miners have more
computing power, they can always outpace an attacker.

Also see [http://en.wikipedia.org/wiki/SHA2 SHA2] and [http://en.wikipedia.org/wiki/Proof-of-work_system Proof-of-work system] on Wikipedia.

===Why was the "Generate coin" option of the client software removed?===

In the early days of Bitcoin, it was easy for anyone to find new blocks using standard CPUs. As more and more people started mining, the [[difficulty]] of finding new blocks has greatly increased to the point where the average time for a CPU to find a single block can be many years. The only cost-effective method of [[Mining|mining]] is using a high-end graphics card with special software (see also [[Why a GPU mines faster than a CPU]]) and/or joining a [[Bitcoin Pool|mining pool]]. Since solo CPU mining is essentially useless, it was removed from the GUI of the Bitcoin software.

==Security==

===Could miners collude to give themselves money or to fundamentally change the nature of Bitcoin?===

There are two questions in here. Let's look at them separately.

;Could miners gang up and give themselves money?

Mining itself is the process of creating new blocks in the block chain. Each block contains a list of all the transactions that have taken place across the entire Bitcoin network since the last block was created, as well as a hash of the previous block. New blocks are 'mined', or rather, generated, by Bitcoin clients correctly guessing sequences of characters in codes called 'hashes,' which are created using information from previous blocks. Bitcoin users may download specialized 'mining' software, which allows them to dedicate some amount of their processing power – however large or small – to guessing at strings within the hash of the previous block. Whoever makes the right guess first, thus creating a new block, receives a reward in Bitcoins.

The block chain is one of the two structures that makes Bitcoin secure, the other being the public-key encryption system on which Bitcoin trade is based. The block chain assures that not only is every single transaction that ever takes place recorded, but that every single transaction is recorded on the computer of anyone who chooses to store the relevant information. Many, many users have complete records of every transaction in Bitcoins history readily available to them at any point, and anyone who wants in the information can obtain it with ease. These things make Bitcoin very hard to fool.

The Bitcoin network takes considerable processing power to run, and since those with the most processing power can make the most guesses, those who put the most power toward to sustaining the network earn the most currency. Each correct guess yields, at present, fifty Bitcoins, and as Bitcoins are presently worth something (although the value still fluctuates) every miner who earns any number of Bitcoins makes money. Some miners pull in Bitcoins on their own; and some also join or form pools wherein all who contribute earn a share of the profits.

Therefore, first answer is a vehement “yes” – no only can miners collude to get more money, Bitcoin is designed to encourage them to do so. Bitcoin pools are communal affairs, and there is nothing dishonest or underhanded about them.

Of course, the real question is:

;Can they do so in ways not sanction by Bitcoin developers? Is there any way to rip off the network and make loads of money dishonestly?

Bitcoin isn't infallible. It can be cheated, but doing so is extremely difficult. Bitcoin was designed to evade some of the central problems with modern currencies – namely, that their trustworthiness hinges upon that of people who might not have users' best interests in mind. Every currency in the world (other than Bitcoin) is controlled by large institutions who keep track of what's done with done with it, and who can manipulate its value. And every other currency has value because people trust the institutions that control them.

Bitcoin doesn't ask that its users trust any institution. Its security is based on the cryptography that is an integral part of its structure, and that is readily available for any and all to see. Instead of one entity keeping track of transactions, the entire network does, so Bitcoins are astoundingly difficult to steal, or double-spend. Bitcoins are created in a regular and predictable fashion, and by many different users, so no one can decide to make a whole lot more and lessen their value. In short, Bitcoin is designed to be inflation-proof, double-spend-proof and completely distributed.

Nonetheless, there are a few ways that one can acquire Bitcoins dishonestly. Firstly, one can steal private keys. Key theft isn't something that Bitcoin security has been designed to prevent: it's up to users to keep theirs safe. But the cryptography is designed so that it is completely impossible to deduce someone's private from their public one. As long as you keep your private key to yourself, you don't have much to worry about. Furthermore, one could theoretically create a new block chain, but due to the way in which the block chain is constructed, this would be extremely difficult and require massive amounts of processing power. A full explanation of the difficulties involved can be found in the [[block chain]] article.

Bitcoin can be ripped off – but doing so would be extremely hard and require considerable expertise and a staggering amount of processing power. And it's only going to get harder with time. Bitcoin isn't impenetrable, but it's close enough to put any real worries in the peripherals.

;Could miners fundamentally change the nature of Bitcoin?

Once again, almost certainly not.

Bitcoin is a distributed network, so any changes implemented to the system must be accepted by all users. Someone trying to change the way Bitcoins are generated would have to convince every user to download and use their software – so the only changes that would go through are those that would be equally benefit all users.

And thus, it is more or less impossible for anyone to change the function of Bitcoin to their advantage. If users don't like the changes, they won't adopt them, whereas if users do like them, then these will help everyone equally. Of course, one can conceive of a situation where someone manages to get a change pushed through that provides them with an advantage that no one notices, but given that Bitcoin is structurally relatively simple, it is unlikely that any major changes will go through without someone noticing first.

The fact that such changes are so difficult to make testifies to the fully distributed nature of Bitcoin. Any centrally controlled currency can be modified by its central agency without the consent of its adherents. Bitcoin has no central authority, so it changes only at the behest of the whole community. Bitcoins development represents a kind of collective evolution; the first of its kind among currencies.

==Help==
===I'd like to learn more. Where can I get help?===

* Read the [[Introduction|introduction to bitcoin]]
* See the videos, podcasts, and blog posts from the [[Press]]
* Read and post on the [[Bitcoin:Community_portal#Bitcoin_Community_Forums|forums]]
* Chat on one of the [[Bitcoin:Community_portal#IRC_Chat|Bitcoin IRC]] channels
* Listen to [http://omegataupodcast.net/2011/03/59-bitcoin-a-digital-decentralized-currency/ this podcast], which goes into the details of how bitcoin works
* Ask questions on the [http://bitcoin.stackexchange.com Bitcoin Stack Exchange]

==See Also==

* [[Man page]]
* [[Introduction]]

[[de:FAQ]]
[[zh-cn:FAQ]]
[[fr:FAQ]]
[[ru:FAQ]]

[[Category:Technical]]
[[Category:Vocabulary]]

Help:FAQ

2012-10-25T15:27:52Z

Jepo: /* Do I need to configure my firewall to run bitcoin? */

Here you will find answers to the most commonly asked questions.

== General ==
=== What are bitcoins? ===
Bitcoins are the unit of currency of the Bitcoin system. A commonly used shorthand for this is “BTC” to refer to a price or amount (eg: “100 BTC”).
There are such things as [[physical bitcoins]], but ultimately, a bitcoin is just a number associated with a [[Address|Bitcoin Address]]. A physical bitcoin is simply an object, such as a coin, with the number carefully embedded inside. See also an [[Introduction|easy intro]] to bitcoin.

=== How can I get bitcoins? ===

There are a variety of ways to acquire bitcoins:

* Accept bitcoins as payment for goods or services.
* There are several services where you can [[buying bitcoins|trade them]] for traditional currency.
* Find someone to trade cash for bitcoins in-person through a [https://en.bitcoin.it/wiki/Category:Directories local directory].
* Participate in a [[Pooled mining|mining pool]].
* If you have a lot of mining hardware, you can solo mine and attempt to create a new [[block]] (currently yields 50 bitcoins).

===Does Bitcoin guarantee an influx of free money?===

Since Bitcoin is a new technology, what it is and how it works may be initially unclear. Bitcoin is sometimes presented as being one of three things:

'''A)''' Some sort of online 'get-rich-quick' scam.

'''B)''' A loophole in the market economy, the installation of which guarantees a steady influx of cash.

'''C)''' A sure investment that will almost certainly yield a profit.

In fact, none of the above are true. Let's look at them independently.

;Is Bitcoin a 'get-rich-quick' scheme?

If you've spent much time on the Internet, you've probably seen ads for many 'get-rich-quick' schemes. These ads usually promise huge profits for a small amounts of easy work. Such schemes are usually pyramid/matrix-style schemes that make money from their own employees and offer nothing of any real value. Most convince one to buy packages that will make them earn hundreds a day, which in fact have the buyer distribute more such ads, and make minute profits.

Bitcoin is in no way similar to these schemes. Bitcoin doesn't promise windfall profits. There is no way for the developers to make money from your involvement or to take money from you. That bitcoins are nearly impossible to acquire without the owner's consent represents one of its greatest strengths. Bitcoin is an experimental, virtual currency that may succeed or may fail. None of its developers expect to get rich off of it.

A more detailed answer to this question can be found [http://bitcointalk.org/?topic=7815.0 here].

;Will I make money by installing the client?

Most people who use Bitcoin don't earn anything by doing so, and the default client has no built-in way to earn Bitcoins. A small minority of people with dedicated, high-performance hardware do earn some Bitcoins by "''mining''" (generating new bitcoins) with special software, but joining Bitcoin shouldn't be construed as being the road to riches. Most Bitcoin users get involved because they find the project conceptually interesting and don't earn anything by doing so. This is also why you won't find much speculation about the political or economic repercussions of Bitcoin anywhere on this site: Bitcoin developers owe their dedication to the project's intellectual yieldings more than to those of a monetary nature. Bitcoin is still taking its first baby steps; it may go on to do great things but right now it only has something to offer those chasing conceptually interesting projects or bleeding edge technology.

;As an investment, is Bitcoin a sure thing?

Bitcoin is a new and interesting electronic currency, the value of which is not backed by any single government or organization. Like other currencies, it is worth something partly because people are willing to trade it for goods and services. Its exchange rate fluctuates continuously, and sometimes wildly. It lacks wide acceptance and is vulnerable to manipulation by parties with modest funding. Security incidents such as website and account compromise may trigger major sell-offs. Other fluctuations can build into positive feedback loops cause much larger exchange rate fluctuations. Anyone who puts money into Bitcoin should take measures to reduce their risk and consider it as a high-risk currency. Later, as Bitcoin becomes better known and more widely accepted, it should stabilize, but for the time being it is unpredictable. Any investment in Bitcoin should be done carefully and with a clear plan to manage risk.

=== Can I buy bitcoins with Paypal? ===

It is possible to buy [[physical bitcoins]] with PayPal but it is otherwise difficult and/or expensive to do so, because of significant risk to the seller.

While it is possible to find an individual who wishes to sell Bitcoin to you via Paypal, (perhaps via [http://www.bitcoin-otc.com/ #bitcoin-otc] ) most exchanges do not allow funding through PayPal. This is due to repeated cases where someone pays for bitcoins with Paypal receives their bitcoins, and then fraudulently complains to Paypal that they never received their purchase. PayPal often sides with the fraudulent buyer in this case which means any seller would need to cover that risk with higher fees or refuse to accept PayPal altogether.

Buying Bitcoins from individuals with this method is still possible, but requires the seller to have some trust that the buyer will not file a claim with PayPal to reverse the payment.

=== Where can I find a forum to discuss Bitcoin? ===

Please visit the [[Bitcoin:Community_portal#Bitcoin_Community_Forums_on_various_platforms|Community Portal]] for links to Bitcoin-related forums.

=== How are new bitcoins created? ===

[[File:total_bitcoins_over_time_graph.png|thumb|Number of bitcoins over time, assuming a perfect 10-minute interval.]]
New bitcoins are generated by the network through the process of mining. In a process that is similar to a continuous lottery, mining nodes on the network are awarded bitcoins each time they find the solution to a certain mathematical problem (and thereby create a new [[block]]). Creating a block is a [[proof of work]] with a difficulty that varies with the overall strength of the network. The reward for solving a block is [[Controlled Currency Supply|automatically adjusted]] so that in roughly the first four years of operation of the Bitcoin network, 10,500,000 BTC will be created. This amount is halved each four years, so it will be 5,250,000 over years 4-8, 2,625,000 over years 8-12 and so on. Thus the total number of bitcoins in existence will not exceed 21,000,000. See [[Controlled Currency Supply]].

Blocks are [[Mining|mined]] every 10 minutes, on average and for the first four years (210,000 blocks) each block includes 50 new bitcoins. As the amount of processing power directed at mining changes, the difficulty of creating new bitcoins changes. This difficulty factor is calculated every 2016 blocks and is based upon the time taken to generate the previous 2016 blocks. See [[Mining]].

=== What's the current total number of Bitcoins in existence? ===

[http://blockexplorer.com/q/totalbc Current count]. Also see [https://blockchain.info/charts/total-bitcoins Total Bitcoins in circulation chart]

The number of blocks times the coin value of a block is the number of coins in existence. The coin value of a block is 50 BTC for each of the first 210,000 blocks, 25 BTC for the next 210,000 blocks, then 12.5 BTC, 6.25 BTC and so on.

=== How divisible are Bitcoins? ===

A bitcoin can be divided down to 8 decimal places. Therefore, 0.00000001 BTC is the smallest amount that can be handled in a transaction. If necessary, the protocol and related software can be modified to handle even smaller amounts.

=== What do I call the various denominations of Bitcoins? ===

There is a lot of discussion about the naming of these fractions of Bitcoins. The leading candidates are:

* 1 BTC = 1 Bitcoin
* 0.01 BTC = 1 cBTC = 1 Centi-Bitcoin (also referred to as Bitcent)
* 0.001 BTC = 1 mBTC = 1 Milli-Bitcoin (also referred to as mbit (pronounced em-bit) or millibit or even bitmill)
* 0.000 001 BTC = 1 μBTC = 1 Micro-Bitcoin (also referred to as ubit (pronounced yu-bit) or microbit)

The above follows the accepted international SI prefixes for hundredths, thousandths, and millionths. There are many arguments against the special case of 0.01 BTC since it is unlikely to represent anything meaningful as the Bitcoin economy grows (it certainly won't be the equivalent of 0.01 USD, GBP or EUR). Equally, the inclusion of existing national currency denominations such as "cent", "nickel", "dime", "pence", "pound", "kopek" and so on are to be discouraged. This is a worldwide currency.

One exception is the "satoshi" which is smallest denomination currently possible

* 0.000 000 01 BTC = 1 Satoshi (pronounced sa-toh-shee)

which is so named in honour of Satoshi Nakamoto the pseudonym of the inventor of Bitcoin.

For an overview of all defined units of Bitcoin (including less common and niche units), see [[Units]].

Further discussion on this topic can be found on the forums here:

* [http://forum.bitcoin.org/index.php?topic=14438.msg195287#msg195287 We need names]
* [http://forum.bitcoin.org/index.php?topic=8282.0 What to call 0.001 BTC]

=== How does the halving work when the number gets really small? ===

Eventually the reward will go from 0.00000001 BTC to zero and no more bitcoins will be created.

The block reward calculation is done as a right bitwise shift of a 64-bit signed integer, which means it is divided by two and rounded down. The integer is equal to the value in BTC * 100,000,000 since internally in the reference client software, all Bitcoin balances and values are stored as unsigned integers.

With an initial block reward of 50 BTC, it will take many 4-year periods for the block reward to reach zero.

=== How long will it take to generate all the coins? ===

The last block that will generate coins will be block #6,929,999 which should be generated at or near the year 2140. The total number of coins in circulation will then remain static at 20,999,999.9769 BTC.

Even if the allowed precision is expanded from the current 8 decimals, the total BTC in circulation will always be slightly below 21 million (assuming everything else stays the same). For example, with 16 decimals of precision, the end total would be 20,999,999.999999999496 BTC.

=== If no more coins are going to be generated, will more blocks be created? ===

Absolutely! Even before the creation of coins ends, the use of [[transaction fee|transaction fees]] will likely make creating new blocks more valuable from the fees than the new coins being created. When coin generation ends, these fees will sustain the ability to use bitcoins and the Bitcoin network. There is no practical limit on the number of blocks that will be mined in the future.

=== But if no more coins are generated, what happens when Bitcoins are lost? Won't that be a problem? ===

Because of the law of supply and demand, when fewer bitcoins are available the ones that are left will be in higher demand, and therefore will have a higher value. So, as Bitcoins are lost, the remaining bitcoins will eventually increase in value to compensate. As the value of a bitcoin increases, the number of bitcoins required to purchase an item '''de'''creases. This is a [[Deflationary spiral|deflationary economic model]]. As the average transaction size reduces, transactions will probably be denominated in sub-units of a bitcoin such as millibitcoins ("Millies") or microbitcoins ("Mikes").

The Bitcoin protocol uses a base unit of one hundred-millionth of a Bitcoin ("a Satoshi"), but unused bits are available in the protocol fields that could be used to denote even smaller subdivisions.

=== If every transaction is broadcast via the network, does Bitcoin scale? ===
The Bitcoin protocol allows lightweight clients that can use Bitcoin without downloading the entire transaction history. As traffic grows and this becomes more critical, implementations of the concept will be developed. Full network nodes will at some point become a more specialized service.

With some modifications to the software, full Bitcoin nodes could easily keep up with both VISA and MasterCard combined, using only fairly modest hardware (a single high end server by todays standards). It is worth noting that the MasterCard network is structured somewhat like Bitcoin itself - as a peer to peer broadcast network.

Learn more about [[Scalability]].

==Economy==
=== Where does the value of Bitcoin stem from? What backs up Bitcoin? ===
Bitcoins have value because they are useful and because they are [[Controlled Currency Supply|scarce]]. As they are accepted by more merchants, their value will [http://en.wikipedia.org/wiki/Sticky_%28economics%29 stabilize]. See the [[Trade|list of Bitcoin-accepting sites]].

When we say that a currency is backed up by gold, we mean that there's a promise in place that you can exchange the currency for gold. Bitcoins, like dollars and euros, are not backed up by anything except the variety of merchants that accept them.

It's a common misconception that Bitcoins gain their value from the cost of electricity required to generate them. Cost doesn't equal value – hiring 1,000 men to shovel a big hole in the ground may be costly, but not valuable. Also, even though scarcity is a critical requirement for a useful currency, it alone doesn't make anything valuable. For example, your fingerprints are scarce, but that doesn't mean they have any exchange value.

=== Is Bitcoin a bubble? ===
Yes, in the same way as the euro and dollar are. They only have value in exchange and have no inherent value. If everyone suddenly stopped accepting your dollars, euros or bitcoins, the "bubble" would burst and their value would drop to zero. But that is unlikely to happen: even in Somalia, where the government collapsed 20 years ago, [http://en.wikipedia.org/wiki/Somali_shilling Somali shillings] are still accepted as payment.

=== Is Bitcoin a Ponzi scheme? ===
In a Ponzi Scheme, the founders persuade investors that they’ll profit. Bitcoin does not make such a guarantee. There is no central entity, just individuals building an economy.

A ponzi scheme is a zero sum game. Early adopters can only profit at the expense of late adopters. Bitcoin has possible win-win outcomes. Early adopters profit from the rise in value. Late adopters, and indeed, society as a whole, benefit from the usefulness of a stable, fast, inexpensive, and widely accepted p2p currency.

The fact that early adopters benefit more doesn't alone make anything a Ponzi scheme. All good investments in successful companies have this quality.

=== Doesn't Bitcoin unfairly benefit early adopters? ===
Early adopters have a large number of bitcoins now because they took a risk and invested resources in an unproven technology. By so doing, they have helped Bitcoin become what it is now and what it will be in the future (hopefully, a ubiquitous decentralized digital currency). It is only fair they will reap the benefits of their successful investment.

In any case, any bitcoin generated will probably change hands dozens of time as a medium of exchange, so the profit made from the initial distribution will be insignificant compared to the total commerce enabled by Bitcoin.

Since the pricing of Bitcoins has fallen greatly from its June 2011 peak, prices today are much more similar to those enjoyed by many early adopters. Those who are buying Bitcoins today likely believe that Bitcoin will grow significantly in the future. Setting aside the brief opportunity to have sold Bitcoins at the June 2011 peak enjoyed by few, the early-adopter window is arguably still open.

===Won't loss of wallets and the finite amount of Bitcoins create excessive deflation, destroying Bitcoin? ===
Worries about Bitcoin being destroyed by deflation are not entirely unfounded. Unlike most currencies, which experience inflation as their founding institutions create more and more units, Bitcoin will likely experience gradual deflation with the passage of time. Bitcoin is unique in that only a small amount of units will ever be produced (twenty-one million to be exact), this number has been known since the project's inception, and the units are created at a predicable rate.

Also, Bitcoin users are faced with a danger that doesn't threaten users of any other currency: if a Bitcoin user loses his wallet, his money is gone forever, unless he finds it again. And not just to him; it's gone completely out of circulation, rendered utterly inaccessible to anyone. As people will lose their wallets, the total number of Bitcoins will slowly decrease.

Therefore, Bitcoin seems to be faced with a unique problem. Whereas most currencies inflate over time, Bitcoin will mostly likely do the just the opposite. Time will see the irretrievable loss of an ever-increasing number of Bitcoins. An already small number will be permanently whittled down further and further. And as there become fewer and fewer Bitcoins, the laws of supply and demand suggest that their value will probably continually rise.

Thus Bitcoin is bound to once again stray into mysterious territory, because no one exactly knows what happens to a currency that grows continually more valuable. Economists generally agree that a low level of inflation is a good thing for a currency, but nobody is quite sure about what might happens to one that continually deflates. Although deflation could hardly be called a rare phenomenon, steady, constant deflation is unheard of. There may be a lot of speculation, no one has any hard data to back up their claims.

That being said, there is a mechanism in place to combat the obvious consequences. Extreme deflation would render most currencies highly impractical: if a single Canadian dollar could suddenly buy the holder a car, how would one go about buying bread or candy? Even pennies would fetch more than a person could carry. Bitcoin, however, offers a simple and stylish solution: infinite divisibility. Bitcoins can be divided up and trade into as small of pieces as one wants, so no matter how valuable Bitcoins become, one can trade them in practical quantities.

In fact, infinite divisibility should allow Bitcoins to function in cases of extreme wallet loss. Even if, in the far future, so many people have lost their wallets that only a single Bitcoin, or a fraction of one, remains, Bitcoin should continue to function just fine. No one can claim to be sure what is going to happen, but deflation may prove to present a smaller threat than many expect.

For more information, see the [[Deflationary spiral]] page.

=== What if someone bought up all the existing Bitcoins? ===
Bitcoin markets are competitive -- meaning the price of a bitcoin will rise or fall depending on supply and demand at certain price levels. Only a fraction of bitcoins issued to date are found on the exchange markets for sale. So even though technically a buyer with lots of money could buy all the bitcoins offered for sale, unless those holding the rest of the bitcoins offer them for sale as well, even the wealthiest, most determined buyer can't get at them.

Additionally, new currency continues to be issued daily and will continue to do so for decades though over time the rate at which they are issued declines to insignificant levels. Those who are mining aren't obligated to sell their bitcoins so not all bitcoins will make it to the markets even.

This situation doesn't suggest, however, that the markets aren't vulnerable to price manipulation. It doesn't take significant amounts of money to move the market price up or down and thus Bitcoin remains a volatile asset.

===What if someone creates a new block chain, or a new digital currency that renders Bitcoin obsolete?===

That the block chain cannot be easily forked represents one of the central security mechanisms of Bitcoin. Given the choice between two block chains, a Bitcoin miner always chooses the longer one - that is to say, the one with the more complex hash. Thusly, it ensures that each user can only spend their bitcoins once, and that no user gets ripped off.

As a consequence of the block chain structure, there may at any time be many different sub-branches, and the possibility always exists of a transaction being over-written by the longest branch, if it has been recorded in a shorter one. The older a transaction is though, the lower its chances of being over-written, and the higher of becoming permanent. Although the block chain prevents one from spending more Bitcoins than one has, it means that transactions can be accidentally nullified.

A new block chain would leave the network vulnerable to [[double-spending|double-spend]] attacks. However, the creation of a viable new chain presents considerable difficulty, and the possibility does not present much of a risk.

Bitcoin will always choose the longer Block Chain and determines the relative length of two branches by the complexities of their hashes. Since the hash of each new block is made from that of the block preceding it, to create a block with a more complex hash, one must be prepared to do more computation than has been done by the entire Bitcoin network from the fork point up to the newest of the blocks one is trying to supersede. Needless to say, such an undertaking would require a very large amount of processing power and since Bitcoin is continually growing and expanding, it will likely only require more with the passage of time.

A much more distinct and real threat to the Bitcoin use is the development of other, superior virtual currencies, which could supplant Bitcoin and render it obsolete and valueless.

A great deal of careful thought and ingenuity has gone into the development of Bitcoin, but it is the first of its breed, a prototype, and vulnerable to more highly-evolved competitors. At present, any threatening rivals have yet to rear its head; Bitcoin remains the first and foremost private virtual currency, but we can offer no guarantees that it will retain that position. It would certainly be in keeping with internet history for similar system built from the same principles to supersede and cast Bitcoin into obsolescence, after time had revealed its major shortcomings. Friendster and Myspace suffered similar fates at the hand of Facebook, Napster was ousted by Limeware, Bearshare and torrent applications, and Skype has all but crushed the last few disciples of the Microsoft Messenger army.

This may sound rather foreboding, so bear in mind that introduction of new and possibly better virtual currencies will not necessarily herald Bitcoin's demise. If Bitcoin establishes itself sufficiently firmly before the inception of the next generation of private, online currencies as to gain widespread acceptance and general stability, future currencies may pose little threat even if they can claim superior design.

==Sending and Receiving Payments==

=== Why do I have to wait 10 minutes before I can spend money I received? ===

10 minutes is the average time taken to find a block. It can be significantly more or less time than that depending on luck; 10 minutes is simply the average case.

You can see how long all other recent transactions have taken here: [http://bitcoinstats.org/ BitcoinStats.org].

[[Blocks]] (shown as "confirmations" in the GUI) are how the Bitcoin achieves consensus on who owns what. Once a block is found everyone agrees that you now own those coins, so you can spend them again. Until then it's possible that some network nodes believe otherwise, if somebody is attempting to defraud the system by reversing a transaction. The more confirmations a transaction has, the less risk there is of a reversal. Only 6 blocks or 1 hour is enough to make reversal computationally impractical. This is dramatically better than credit cards which can see chargebacks occur up to three months after the original transaction!

Ten minutes was specifically chosen by [[Satoshi]] as a tradeoff between propagation time of new blocks in large networks and the amount of work wasted due to chain splits. For a more technical explanation, see Satoshi's [http://www.bitcoin.org/bitcoin.pdf original technical paper].

[[File:TransactionConfirmationTimesExample.PNG]]

=== Do you have to wait until my transactions are confirmed in order to buy or sell things with Bitcoin? ===

YES, you do, IF the transaction is non-recourse. The Bitcoin reference software does not display transactions as confirmed until six blocks have passed (confirmations). As transactions are burred in the chain they become increasingly non-reversible but are very reversible before the first confirmation. Two to six confirmations are recommended for non-recourse situations depending on the value of the transactions involved.

When people ask this question they are usually thinking about applications like supermarkets. This generally is a recourse situation: if somebody tries to double-spend on a face-to-face transaction it might work a few times, but probabalistically speaking eventually one of the double-spends will get noticed, and the penalty for shoplifting charges in most localities is calibrated to be several times worse than the proceeds of a single shoplifting event.

Double-spends might be a concern for something like a snack machine in a low-traffic area with no nearby security cameras. Such a machine shouldn't honor 0-confirmation payments, and should instead use some other mechanism of clearing Bitcoin or validating transactions against reversal, see the wiki article [[Myths#Point_of_sale_with_bitcoins_isn.27t_possible_because_of_the_10_minute_wait_for_confirmation|here]] for alternatives.

When people ask this question they are usually thinking about applications that require immediate payment processing, like supermarkets or snack machines. Here is one way to reverse an unconfirmed payment:

A [[Double-spending#Finney_attack|Finney attack]], in which an attacker mines a block containing a movement of some coins back to themselves. Once they find a block solution, they quickly go to a merchant and make a purchase, then broadcast the block, thus taking back the coins. This attack is a risk primarily for goods that are dispatched immediately, like song downloads or currency trades. Because the attacker can't choose the time of the attack, it isn't a risk for merchants such as supermarkets where you can't choose exactly when to pay (due to queues, etc). The attack can fail if somebody else finds a block containing the purchasing transaction before you release your own block, therefore, merchants can reduce but not eliminate the risk by making purchasers wait some length of time that's less than a confirm.

Because pulling off this attack is not trivial, merchants who need to sell things automatically and instantly are most likely to just price the cost of reversal fraud in, or use insurance.

=== I was sent some bitcoins and they haven't arrived yet! Where are they? ===

Don't panic! There are a number of reasons why your bitcoins might not show up yet, and a number of ways to diagnose them.

The latest version of the Bitcoin-Qt client tells you how far it has yet to go in downloading the blockchain. Hover over the icon in the bottom right corner of the client to learn your client's status.

If it has not caught up then it's possible that your transaction hasn't been included in a block yet.

You can check pending transactions in the network by going [http://blockchain.info here] and then searching for your address. If the transaction is listed here then it's a matter of waiting until it gets included in a block before it will show in your client.

Bear in mind that if the transaction is based on a coin that was in a recent transaction then it could be considered a low priority transaction take longer to transfer if the transaction fee paid isn't high enough. Very low priority transactions with 0 fees might take hours or days to be included in a block.

=== Why does my Bitcoin address keep changing? ===

Whenever the address listed in "Your address" receives a transaction, Bitcoin replaces it with a new address. This is meant to encourage you to use a new address for every transaction, which enhances [[anonymity]]. All of your old addresses are still usable: you can see them in ''Settings -> Your Receiving Addresses''.

===How much will the transaction fee be?===

Some transactions might require a [[transaction fee]] for them to get confirmed in a timely manner. The transaction fee is processed by and received by the bitcoin miner. The most recent version of the Bitcoin client will estimate an appropriate fee when a fee might be required.

The fee is added to the payment amount. For example, if you are sending a 1.234 BTC payment and the client requires a 0.0005 BTC fee, then 1.2345 BTC will be subtracted from the wallet balance for the entire transaction and the address for where the payment was sent will receive a payment of 1.234 BTC.

In cases where a fee is required it is required because your transaction objectively looks like a denial of service attack to the bitcoin system, either due to it being burdensome to transmit or it recycles bitcoins you recently received. The wallet software attempts to avoid generating burdensome transactions, but it isn't always able if the funds in your wallet are new or are composed of many very tiny payments.

Because the fee is related to the amount of data that makes up the transaction and not to the amount of bitcoins being sent, the fee may seem extremely low (0.0005 BTC for a 1,000 BTC transfer) or unfairly high (0.004 BTC for a 0.02 BTC payment, or about 20%). If you are receiving tiny amounts (e.g., as small payments from a mining pool) then fees when sending will be higher than if your activity follows a more normal consumer or business transaction pattern. As of bitcoin 0.5.3 the required fee it will ask for will not be higher than 0.05 BTC, though for most users there is usually no required fee at all and 0.0005 is the most common when one is required.

=== What happens when someone sends me a bitcoin but my computer is powered off? ===

Bitcoins aren't actually "sent" to your wallet, the software only uses that term so that we can use the currency without having to learn new concepts. Your wallet is only needed when you wish to spend coins that you've received.

The coins that were sent to you when the client was not running will later appear as if they were received in your wallet when you later launch the client. It will download blocks and catch up with any transactions it didn't already have.

=== How long does "synchronizing" take when the Bitcoin client is first installed? What's it doing? ===

The popular Bitcoin client software from bitcoin.org implements a "full" Bitcoin node: It can carry out all the duties of the Bitcoin P2P system, it isn't simply a "client". One of the principles behind the operation of full Bitcoin nodes is that they don't assume that the other participants have followed the rules of the Bitcoin system. During synchronization, the software is processing historical Bitcoin transactions and making sure for itself that all of the rules of the system have been correctly followed.

In normal operation, after synchronizing, the software should use a hardly noticeable amount of IO, CPU, or network capacity.

The initial validation is very disk-IO-intensive, so the amount of time to synchronize depends on your disk speed and, to a lesser extent, your CPU speed. It can take anywhere from a few hours to a day or so. You can use the software while this process is going on, but you may not see recent payments to you until the synchronization has caught up to the point where those transactions happened.

If this is too long for you, you can download a pre-synchronized blockchain from [http://eu1.bitcoincharts.com/blockchain/ http://eu1.bitcoincharts.com/blockchain/]. Alternatively, you can try an alternative "lite" client such as Multibit or a super-light client like electrum, though these clients have somewhat weaker security, are less mature, and don't contribute to the health of the P2P network.

==Networking==
=== Do I need to configure my firewall to run Bitcoin? ===

Bitcoin will connect to other nodes, usually on TCP port 8333. You will need to allow outgoing TCP connections to port 8333 if you want to allow your Bitcoin client to connect to many nodes. [[Testnet]] uses TCP port 18333 instead of 8333.

If you want to restrict your firewall rules to a few IPs, you can find stable nodes in the [[Fallback Nodes|fallback nodes list]].

=== How does the peer finding mechanism work? ===

Bitcoin finds peers primarily by forwarding peer announcements within its own network and each node saves a database of peers that it's aware of, for future use. In order to bootstrap this process Bitcoin needs a list of initial peers, these can be provided manually but normally it obtains them by querying a set of DNS domain names which have automatically updated lists, if that doesn't work it falls back to a build-in list which is updated from time to time in new versions of the software. There is also an IRC based mechanism but it is disabled by default.

==Mining==
===What is mining?===
[[Mining]] is the process of spending computation power to secure Bitcoin transactions against reversal and introducing new Bitcoins to the system.

Technically speaking, mining is the calculation of a [[hash]] of the a block header, which includes among other things a reference to the previous block, a hash of a set of transactions and a [[nonce]]. If the hash value is found to be less than the current [[target]] (which is inversely proportional to the [[difficulty]]), a new block is formed and the miner gets the newly generated Bitcoins (50 per block at current levels). If the hash is not less than the current target, a new nonce is tried, and a new hash is calculated. This is done millions of times per second by each miner.

===Is mining used for some useful computation?===
The computations done when mining are internal to Bitcoin and not related to any other distributed computing projects. They serve the purpose of securing the Bitcoin network, which is useful.

===Is it not a waste of energy?===
Spending energy on creating and securing a free monetary system is hardly a waste. Also, services necessary for the operation of currently widespread monetary systems, such as banks and credit card companies, also spend energy, arguably more than Bitcoin would.

===Why don't we use calculations that are also useful for some other purpose?===
To provide security for the Bitcoin network, the calculations involved need to have some very specific features. These features are incompatible with leveraging the computation for other purposes.

===How can we stop miners from creating zero transaction blocks?===
The incentive for miners to include transactions is in the fees that come along with them. If we were to implement some minimum number of transactions per block it would be trivial for a miner to create and include transactions merely to surpass that threshold. As the network matures, the block reward drops, and miners become more dependent on transactions fees to pay their costs, the problem of zero transaction blocks should diminish over time.

===How does the proof-of-work system help secure Bitcoin?===
To give a general idea of the mining process, imagine this setup:

payload = <some data related to things happening on the Bitcoin network>
nonce = 1
hash = [http://en.wikipedia.org/wiki/SHA2 SHA2]( [http://en.wikipedia.org/wiki/SHA2 SHA2]( payload + nonce ) )

The work performed by a miner consists of repeatedly increasing "nonce" until
the hash function yields a value, that has the rare property of being below a certain
target threshold. (In other words: The hash "starts with a certain number of zeroes",
if you display it in the fixed-length representation, that is typically used.)

As can be seen, the mining process doesn't compute anything special. It merely
tries to find a number (also referred to as nonce) which - in combination with the payload -
results in a hash with special properties.

The advantage of using such a mechanism consists of the fact, that it is very easy to check a result: Given the payload and a specific nonce, only a single call of the hashing function is needed to verify that the hash has the required properties. Since there is no known way to find these hashes other than brute force, this can be used as a "proof of work" that someone invested a lot of computing power to find the correct nonce for this payload.

This feature is then used in the Bitcoin network to secure various aspects. An attacker
that wants to introduce malicious payload data into the network, will need to do the
required proof of work before it will be accepted. And as long as honest miners have more
computing power, they can always outpace an attacker.

Also see [http://en.wikipedia.org/wiki/SHA2 SHA2] and [http://en.wikipedia.org/wiki/Proof-of-work_system Proof-of-work system] on Wikipedia.

===Why was the "Generate coin" option of the client software removed?===

In the early days of Bitcoin, it was easy for anyone to find new blocks using standard CPUs. As more and more people started mining, the [[difficulty]] of finding new blocks has greatly increased to the point where the average time for a CPU to find a single block can be many years. The only cost-effective method of [[Mining|mining]] is using a high-end graphics card with special software (see also [[Why a GPU mines faster than a CPU]]) and/or joining a [[Bitcoin Pool|mining pool]]. Since solo CPU mining is essentially useless, it was removed from the GUI of the Bitcoin software.

==Security==

===Could miners collude to give themselves money or to fundamentally change the nature of Bitcoin?===

There are two questions in here. Let's look at them separately.

;Could miners gang up and give themselves money?

Mining itself is the process of creating new blocks in the block chain. Each block contains a list of all the transactions that have taken place across the entire Bitcoin network since the last block was created, as well as a hash of the previous block. New blocks are 'mined', or rather, generated, by Bitcoin clients correctly guessing sequences of characters in codes called 'hashes,' which are created using information from previous blocks. Bitcoin users may download specialized 'mining' software, which allows them to dedicate some amount of their processing power – however large or small – to guessing at strings within the hash of the previous block. Whoever makes the right guess first, thus creating a new block, receives a reward in Bitcoins.

The block chain is one of the two structures that makes Bitcoin secure, the other being the public-key encryption system on which Bitcoin trade is based. The block chain assures that not only is every single transaction that ever takes place recorded, but that every single transaction is recorded on the computer of anyone who chooses to store the relevant information. Many, many users have complete records of every transaction in Bitcoins history readily available to them at any point, and anyone who wants in the information can obtain it with ease. These things make Bitcoin very hard to fool.

The Bitcoin network takes considerable processing power to run, and since those with the most processing power can make the most guesses, those who put the most power toward to sustaining the network earn the most currency. Each correct guess yields, at present, fifty Bitcoins, and as Bitcoins are presently worth something (although the value still fluctuates) every miner who earns any number of Bitcoins makes money. Some miners pull in Bitcoins on their own; and some also join or form pools wherein all who contribute earn a share of the profits.

Therefore, first answer is a vehement “yes” – no only can miners collude to get more money, Bitcoin is designed to encourage them to do so. Bitcoin pools are communal affairs, and there is nothing dishonest or underhanded about them.

Of course, the real question is:

;Can they do so in ways not sanction by Bitcoin developers? Is there any way to rip off the network and make loads of money dishonestly?

Bitcoin isn't infallible. It can be cheated, but doing so is extremely difficult. Bitcoin was designed to evade some of the central problems with modern currencies – namely, that their trustworthiness hinges upon that of people who might not have users' best interests in mind. Every currency in the world (other than Bitcoin) is controlled by large institutions who keep track of what's done with done with it, and who can manipulate its value. And every other currency has value because people trust the institutions that control them.

Bitcoin doesn't ask that its users trust any institution. Its security is based on the cryptography that is an integral part of its structure, and that is readily available for any and all to see. Instead of one entity keeping track of transactions, the entire network does, so Bitcoins are astoundingly difficult to steal, or double-spend. Bitcoins are created in a regular and predictable fashion, and by many different users, so no one can decide to make a whole lot more and lessen their value. In short, Bitcoin is designed to be inflation-proof, double-spend-proof and completely distributed.

Nonetheless, there are a few ways that one can acquire Bitcoins dishonestly. Firstly, one can steal private keys. Key theft isn't something that Bitcoin security has been designed to prevent: it's up to users to keep theirs safe. But the cryptography is designed so that it is completely impossible to deduce someone's private from their public one. As long as you keep your private key to yourself, you don't have much to worry about. Furthermore, one could theoretically create a new block chain, but due to the way in which the block chain is constructed, this would be extremely difficult and require massive amounts of processing power. A full explanation of the difficulties involved can be found in the [[block chain]] article.

Bitcoin can be ripped off – but doing so would be extremely hard and require considerable expertise and a staggering amount of processing power. And it's only going to get harder with time. Bitcoin isn't impenetrable, but it's close enough to put any real worries in the peripherals.

;Could miners fundamentally change the nature of Bitcoin?

Once again, almost certainly not.

Bitcoin is a distributed network, so any changes implemented to the system must be accepted by all users. Someone trying to change the way Bitcoins are generated would have to convince every user to download and use their software – so the only changes that would go through are those that would be equally benefit all users.

And thus, it is more or less impossible for anyone to change the function of Bitcoin to their advantage. If users don't like the changes, they won't adopt them, whereas if users do like them, then these will help everyone equally. Of course, one can conceive of a situation where someone manages to get a change pushed through that provides them with an advantage that no one notices, but given that Bitcoin is structurally relatively simple, it is unlikely that any major changes will go through without someone noticing first.

The fact that such changes are so difficult to make testifies to the fully distributed nature of Bitcoin. Any centrally controlled currency can be modified by its central agency without the consent of its adherents. Bitcoin has no central authority, so it changes only at the behest of the whole community. Bitcoins development represents a kind of collective evolution; the first of its kind among currencies.

==Help==
===I'd like to learn more. Where can I get help?===

* Read the [[Introduction|introduction to bitcoin]]
* See the videos, podcasts, and blog posts from the [[Press]]
* Read and post on the [[Bitcoin:Community_portal#Bitcoin_Community_Forums|forums]]
* Chat on one of the [[Bitcoin:Community_portal#IRC_Chat|Bitcoin IRC]] channels
* Listen to [http://omegataupodcast.net/2011/03/59-bitcoin-a-digital-decentralized-currency/ this podcast], which goes into the details of how bitcoin works
* Ask questions on the [http://bitcoin.stackexchange.com Bitcoin Stack Exchange]

==See Also==

* [[Man page]]
* [[Introduction]]

[[de:FAQ]]
[[zh-cn:FAQ]]
[[fr:FAQ]]
[[ru:FAQ]]

[[Category:Technical]]
[[Category:Vocabulary]]

Help:FAQ

2012-10-25T15:26:38Z

Jepo: /* How long does "synchronizing" take when the bitcoin client is first installed? What is it doing? */

Here you will find answers to the most commonly asked questions.

== General ==
=== What are bitcoins? ===
Bitcoins are the unit of currency of the Bitcoin system. A commonly used shorthand for this is “BTC” to refer to a price or amount (eg: “100 BTC”).
There are such things as [[physical bitcoins]], but ultimately, a bitcoin is just a number associated with a [[Address|Bitcoin Address]]. A physical bitcoin is simply an object, such as a coin, with the number carefully embedded inside. See also an [[Introduction|easy intro]] to bitcoin.

=== How can I get bitcoins? ===

There are a variety of ways to acquire bitcoins:

* Accept bitcoins as payment for goods or services.
* There are several services where you can [[buying bitcoins|trade them]] for traditional currency.
* Find someone to trade cash for bitcoins in-person through a [https://en.bitcoin.it/wiki/Category:Directories local directory].
* Participate in a [[Pooled mining|mining pool]].
* If you have a lot of mining hardware, you can solo mine and attempt to create a new [[block]] (currently yields 50 bitcoins).

===Does Bitcoin guarantee an influx of free money?===

Since Bitcoin is a new technology, what it is and how it works may be initially unclear. Bitcoin is sometimes presented as being one of three things:

'''A)''' Some sort of online 'get-rich-quick' scam.

'''B)''' A loophole in the market economy, the installation of which guarantees a steady influx of cash.

'''C)''' A sure investment that will almost certainly yield a profit.

In fact, none of the above are true. Let's look at them independently.

;Is Bitcoin a 'get-rich-quick' scheme?

If you've spent much time on the Internet, you've probably seen ads for many 'get-rich-quick' schemes. These ads usually promise huge profits for a small amounts of easy work. Such schemes are usually pyramid/matrix-style schemes that make money from their own employees and offer nothing of any real value. Most convince one to buy packages that will make them earn hundreds a day, which in fact have the buyer distribute more such ads, and make minute profits.

Bitcoin is in no way similar to these schemes. Bitcoin doesn't promise windfall profits. There is no way for the developers to make money from your involvement or to take money from you. That bitcoins are nearly impossible to acquire without the owner's consent represents one of its greatest strengths. Bitcoin is an experimental, virtual currency that may succeed or may fail. None of its developers expect to get rich off of it.

A more detailed answer to this question can be found [http://bitcointalk.org/?topic=7815.0 here].

;Will I make money by installing the client?

Most people who use Bitcoin don't earn anything by doing so, and the default client has no built-in way to earn Bitcoins. A small minority of people with dedicated, high-performance hardware do earn some Bitcoins by "''mining''" (generating new bitcoins) with special software, but joining Bitcoin shouldn't be construed as being the road to riches. Most Bitcoin users get involved because they find the project conceptually interesting and don't earn anything by doing so. This is also why you won't find much speculation about the political or economic repercussions of Bitcoin anywhere on this site: Bitcoin developers owe their dedication to the project's intellectual yieldings more than to those of a monetary nature. Bitcoin is still taking its first baby steps; it may go on to do great things but right now it only has something to offer those chasing conceptually interesting projects or bleeding edge technology.

;As an investment, is Bitcoin a sure thing?

Bitcoin is a new and interesting electronic currency, the value of which is not backed by any single government or organization. Like other currencies, it is worth something partly because people are willing to trade it for goods and services. Its exchange rate fluctuates continuously, and sometimes wildly. It lacks wide acceptance and is vulnerable to manipulation by parties with modest funding. Security incidents such as website and account compromise may trigger major sell-offs. Other fluctuations can build into positive feedback loops cause much larger exchange rate fluctuations. Anyone who puts money into Bitcoin should take measures to reduce their risk and consider it as a high-risk currency. Later, as Bitcoin becomes better known and more widely accepted, it should stabilize, but for the time being it is unpredictable. Any investment in Bitcoin should be done carefully and with a clear plan to manage risk.

=== Can I buy bitcoins with Paypal? ===

It is possible to buy [[physical bitcoins]] with PayPal but it is otherwise difficult and/or expensive to do so, because of significant risk to the seller.

While it is possible to find an individual who wishes to sell Bitcoin to you via Paypal, (perhaps via [http://www.bitcoin-otc.com/ #bitcoin-otc] ) most exchanges do not allow funding through PayPal. This is due to repeated cases where someone pays for bitcoins with Paypal receives their bitcoins, and then fraudulently complains to Paypal that they never received their purchase. PayPal often sides with the fraudulent buyer in this case which means any seller would need to cover that risk with higher fees or refuse to accept PayPal altogether.

Buying Bitcoins from individuals with this method is still possible, but requires the seller to have some trust that the buyer will not file a claim with PayPal to reverse the payment.

=== Where can I find a forum to discuss Bitcoin? ===

Please visit the [[Bitcoin:Community_portal#Bitcoin_Community_Forums_on_various_platforms|Community Portal]] for links to Bitcoin-related forums.

=== How are new bitcoins created? ===

[[File:total_bitcoins_over_time_graph.png|thumb|Number of bitcoins over time, assuming a perfect 10-minute interval.]]
New bitcoins are generated by the network through the process of mining. In a process that is similar to a continuous lottery, mining nodes on the network are awarded bitcoins each time they find the solution to a certain mathematical problem (and thereby create a new [[block]]). Creating a block is a [[proof of work]] with a difficulty that varies with the overall strength of the network. The reward for solving a block is [[Controlled Currency Supply|automatically adjusted]] so that in roughly the first four years of operation of the Bitcoin network, 10,500,000 BTC will be created. This amount is halved each four years, so it will be 5,250,000 over years 4-8, 2,625,000 over years 8-12 and so on. Thus the total number of bitcoins in existence will not exceed 21,000,000. See [[Controlled Currency Supply]].

Blocks are [[Mining|mined]] every 10 minutes, on average and for the first four years (210,000 blocks) each block includes 50 new bitcoins. As the amount of processing power directed at mining changes, the difficulty of creating new bitcoins changes. This difficulty factor is calculated every 2016 blocks and is based upon the time taken to generate the previous 2016 blocks. See [[Mining]].

=== What's the current total number of Bitcoins in existence? ===

[http://blockexplorer.com/q/totalbc Current count]. Also see [https://blockchain.info/charts/total-bitcoins Total Bitcoins in circulation chart]

The number of blocks times the coin value of a block is the number of coins in existence. The coin value of a block is 50 BTC for each of the first 210,000 blocks, 25 BTC for the next 210,000 blocks, then 12.5 BTC, 6.25 BTC and so on.

=== How divisible are Bitcoins? ===

A bitcoin can be divided down to 8 decimal places. Therefore, 0.00000001 BTC is the smallest amount that can be handled in a transaction. If necessary, the protocol and related software can be modified to handle even smaller amounts.

=== What do I call the various denominations of Bitcoins? ===

There is a lot of discussion about the naming of these fractions of Bitcoins. The leading candidates are:

* 1 BTC = 1 Bitcoin
* 0.01 BTC = 1 cBTC = 1 Centi-Bitcoin (also referred to as Bitcent)
* 0.001 BTC = 1 mBTC = 1 Milli-Bitcoin (also referred to as mbit (pronounced em-bit) or millibit or even bitmill)
* 0.000 001 BTC = 1 μBTC = 1 Micro-Bitcoin (also referred to as ubit (pronounced yu-bit) or microbit)

The above follows the accepted international SI prefixes for hundredths, thousandths, and millionths. There are many arguments against the special case of 0.01 BTC since it is unlikely to represent anything meaningful as the Bitcoin economy grows (it certainly won't be the equivalent of 0.01 USD, GBP or EUR). Equally, the inclusion of existing national currency denominations such as "cent", "nickel", "dime", "pence", "pound", "kopek" and so on are to be discouraged. This is a worldwide currency.

One exception is the "satoshi" which is smallest denomination currently possible

* 0.000 000 01 BTC = 1 Satoshi (pronounced sa-toh-shee)

which is so named in honour of Satoshi Nakamoto the pseudonym of the inventor of Bitcoin.

For an overview of all defined units of Bitcoin (including less common and niche units), see [[Units]].

Further discussion on this topic can be found on the forums here:

* [http://forum.bitcoin.org/index.php?topic=14438.msg195287#msg195287 We need names]
* [http://forum.bitcoin.org/index.php?topic=8282.0 What to call 0.001 BTC]

=== How does the halving work when the number gets really small? ===

Eventually the reward will go from 0.00000001 BTC to zero and no more bitcoins will be created.

The block reward calculation is done as a right bitwise shift of a 64-bit signed integer, which means it is divided by two and rounded down. The integer is equal to the value in BTC * 100,000,000 since internally in the reference client software, all Bitcoin balances and values are stored as unsigned integers.

With an initial block reward of 50 BTC, it will take many 4-year periods for the block reward to reach zero.

=== How long will it take to generate all the coins? ===

The last block that will generate coins will be block #6,929,999 which should be generated at or near the year 2140. The total number of coins in circulation will then remain static at 20,999,999.9769 BTC.

Even if the allowed precision is expanded from the current 8 decimals, the total BTC in circulation will always be slightly below 21 million (assuming everything else stays the same). For example, with 16 decimals of precision, the end total would be 20,999,999.999999999496 BTC.

=== If no more coins are going to be generated, will more blocks be created? ===

Absolutely! Even before the creation of coins ends, the use of [[transaction fee|transaction fees]] will likely make creating new blocks more valuable from the fees than the new coins being created. When coin generation ends, these fees will sustain the ability to use bitcoins and the Bitcoin network. There is no practical limit on the number of blocks that will be mined in the future.

=== But if no more coins are generated, what happens when Bitcoins are lost? Won't that be a problem? ===

Because of the law of supply and demand, when fewer bitcoins are available the ones that are left will be in higher demand, and therefore will have a higher value. So, as Bitcoins are lost, the remaining bitcoins will eventually increase in value to compensate. As the value of a bitcoin increases, the number of bitcoins required to purchase an item '''de'''creases. This is a [[Deflationary spiral|deflationary economic model]]. As the average transaction size reduces, transactions will probably be denominated in sub-units of a bitcoin such as millibitcoins ("Millies") or microbitcoins ("Mikes").

The Bitcoin protocol uses a base unit of one hundred-millionth of a Bitcoin ("a Satoshi"), but unused bits are available in the protocol fields that could be used to denote even smaller subdivisions.

=== If every transaction is broadcast via the network, does Bitcoin scale? ===
The Bitcoin protocol allows lightweight clients that can use Bitcoin without downloading the entire transaction history. As traffic grows and this becomes more critical, implementations of the concept will be developed. Full network nodes will at some point become a more specialized service.

With some modifications to the software, full Bitcoin nodes could easily keep up with both VISA and MasterCard combined, using only fairly modest hardware (a single high end server by todays standards). It is worth noting that the MasterCard network is structured somewhat like Bitcoin itself - as a peer to peer broadcast network.

Learn more about [[Scalability]].

==Economy==
=== Where does the value of Bitcoin stem from? What backs up Bitcoin? ===
Bitcoins have value because they are useful and because they are [[Controlled Currency Supply|scarce]]. As they are accepted by more merchants, their value will [http://en.wikipedia.org/wiki/Sticky_%28economics%29 stabilize]. See the [[Trade|list of Bitcoin-accepting sites]].

When we say that a currency is backed up by gold, we mean that there's a promise in place that you can exchange the currency for gold. Bitcoins, like dollars and euros, are not backed up by anything except the variety of merchants that accept them.

It's a common misconception that Bitcoins gain their value from the cost of electricity required to generate them. Cost doesn't equal value – hiring 1,000 men to shovel a big hole in the ground may be costly, but not valuable. Also, even though scarcity is a critical requirement for a useful currency, it alone doesn't make anything valuable. For example, your fingerprints are scarce, but that doesn't mean they have any exchange value.

=== Is Bitcoin a bubble? ===
Yes, in the same way as the euro and dollar are. They only have value in exchange and have no inherent value. If everyone suddenly stopped accepting your dollars, euros or bitcoins, the "bubble" would burst and their value would drop to zero. But that is unlikely to happen: even in Somalia, where the government collapsed 20 years ago, [http://en.wikipedia.org/wiki/Somali_shilling Somali shillings] are still accepted as payment.

=== Is Bitcoin a Ponzi scheme? ===
In a Ponzi Scheme, the founders persuade investors that they’ll profit. Bitcoin does not make such a guarantee. There is no central entity, just individuals building an economy.

A ponzi scheme is a zero sum game. Early adopters can only profit at the expense of late adopters. Bitcoin has possible win-win outcomes. Early adopters profit from the rise in value. Late adopters, and indeed, society as a whole, benefit from the usefulness of a stable, fast, inexpensive, and widely accepted p2p currency.

The fact that early adopters benefit more doesn't alone make anything a Ponzi scheme. All good investments in successful companies have this quality.

=== Doesn't Bitcoin unfairly benefit early adopters? ===
Early adopters have a large number of bitcoins now because they took a risk and invested resources in an unproven technology. By so doing, they have helped Bitcoin become what it is now and what it will be in the future (hopefully, a ubiquitous decentralized digital currency). It is only fair they will reap the benefits of their successful investment.

In any case, any bitcoin generated will probably change hands dozens of time as a medium of exchange, so the profit made from the initial distribution will be insignificant compared to the total commerce enabled by Bitcoin.

Since the pricing of Bitcoins has fallen greatly from its June 2011 peak, prices today are much more similar to those enjoyed by many early adopters. Those who are buying Bitcoins today likely believe that Bitcoin will grow significantly in the future. Setting aside the brief opportunity to have sold Bitcoins at the June 2011 peak enjoyed by few, the early-adopter window is arguably still open.

===Won't loss of wallets and the finite amount of Bitcoins create excessive deflation, destroying Bitcoin? ===
Worries about Bitcoin being destroyed by deflation are not entirely unfounded. Unlike most currencies, which experience inflation as their founding institutions create more and more units, Bitcoin will likely experience gradual deflation with the passage of time. Bitcoin is unique in that only a small amount of units will ever be produced (twenty-one million to be exact), this number has been known since the project's inception, and the units are created at a predicable rate.

Also, Bitcoin users are faced with a danger that doesn't threaten users of any other currency: if a Bitcoin user loses his wallet, his money is gone forever, unless he finds it again. And not just to him; it's gone completely out of circulation, rendered utterly inaccessible to anyone. As people will lose their wallets, the total number of Bitcoins will slowly decrease.

Therefore, Bitcoin seems to be faced with a unique problem. Whereas most currencies inflate over time, Bitcoin will mostly likely do the just the opposite. Time will see the irretrievable loss of an ever-increasing number of Bitcoins. An already small number will be permanently whittled down further and further. And as there become fewer and fewer Bitcoins, the laws of supply and demand suggest that their value will probably continually rise.

Thus Bitcoin is bound to once again stray into mysterious territory, because no one exactly knows what happens to a currency that grows continually more valuable. Economists generally agree that a low level of inflation is a good thing for a currency, but nobody is quite sure about what might happens to one that continually deflates. Although deflation could hardly be called a rare phenomenon, steady, constant deflation is unheard of. There may be a lot of speculation, no one has any hard data to back up their claims.

That being said, there is a mechanism in place to combat the obvious consequences. Extreme deflation would render most currencies highly impractical: if a single Canadian dollar could suddenly buy the holder a car, how would one go about buying bread or candy? Even pennies would fetch more than a person could carry. Bitcoin, however, offers a simple and stylish solution: infinite divisibility. Bitcoins can be divided up and trade into as small of pieces as one wants, so no matter how valuable Bitcoins become, one can trade them in practical quantities.

In fact, infinite divisibility should allow Bitcoins to function in cases of extreme wallet loss. Even if, in the far future, so many people have lost their wallets that only a single Bitcoin, or a fraction of one, remains, Bitcoin should continue to function just fine. No one can claim to be sure what is going to happen, but deflation may prove to present a smaller threat than many expect.

For more information, see the [[Deflationary spiral]] page.

=== What if someone bought up all the existing Bitcoins? ===
Bitcoin markets are competitive -- meaning the price of a bitcoin will rise or fall depending on supply and demand at certain price levels. Only a fraction of bitcoins issued to date are found on the exchange markets for sale. So even though technically a buyer with lots of money could buy all the bitcoins offered for sale, unless those holding the rest of the bitcoins offer them for sale as well, even the wealthiest, most determined buyer can't get at them.

Additionally, new currency continues to be issued daily and will continue to do so for decades though over time the rate at which they are issued declines to insignificant levels. Those who are mining aren't obligated to sell their bitcoins so not all bitcoins will make it to the markets even.

This situation doesn't suggest, however, that the markets aren't vulnerable to price manipulation. It doesn't take significant amounts of money to move the market price up or down and thus Bitcoin remains a volatile asset.

===What if someone creates a new block chain, or a new digital currency that renders Bitcoin obsolete?===

That the block chain cannot be easily forked represents one of the central security mechanisms of Bitcoin. Given the choice between two block chains, a Bitcoin miner always chooses the longer one - that is to say, the one with the more complex hash. Thusly, it ensures that each user can only spend their bitcoins once, and that no user gets ripped off.

As a consequence of the block chain structure, there may at any time be many different sub-branches, and the possibility always exists of a transaction being over-written by the longest branch, if it has been recorded in a shorter one. The older a transaction is though, the lower its chances of being over-written, and the higher of becoming permanent. Although the block chain prevents one from spending more Bitcoins than one has, it means that transactions can be accidentally nullified.

A new block chain would leave the network vulnerable to [[double-spending|double-spend]] attacks. However, the creation of a viable new chain presents considerable difficulty, and the possibility does not present much of a risk.

Bitcoin will always choose the longer Block Chain and determines the relative length of two branches by the complexities of their hashes. Since the hash of each new block is made from that of the block preceding it, to create a block with a more complex hash, one must be prepared to do more computation than has been done by the entire Bitcoin network from the fork point up to the newest of the blocks one is trying to supersede. Needless to say, such an undertaking would require a very large amount of processing power and since Bitcoin is continually growing and expanding, it will likely only require more with the passage of time.

A much more distinct and real threat to the Bitcoin use is the development of other, superior virtual currencies, which could supplant Bitcoin and render it obsolete and valueless.

A great deal of careful thought and ingenuity has gone into the development of Bitcoin, but it is the first of its breed, a prototype, and vulnerable to more highly-evolved competitors. At present, any threatening rivals have yet to rear its head; Bitcoin remains the first and foremost private virtual currency, but we can offer no guarantees that it will retain that position. It would certainly be in keeping with internet history for similar system built from the same principles to supersede and cast Bitcoin into obsolescence, after time had revealed its major shortcomings. Friendster and Myspace suffered similar fates at the hand of Facebook, Napster was ousted by Limeware, Bearshare and torrent applications, and Skype has all but crushed the last few disciples of the Microsoft Messenger army.

This may sound rather foreboding, so bear in mind that introduction of new and possibly better virtual currencies will not necessarily herald Bitcoin's demise. If Bitcoin establishes itself sufficiently firmly before the inception of the next generation of private, online currencies as to gain widespread acceptance and general stability, future currencies may pose little threat even if they can claim superior design.

==Sending and Receiving Payments==

=== Why do I have to wait 10 minutes before I can spend money I received? ===

10 minutes is the average time taken to find a block. It can be significantly more or less time than that depending on luck; 10 minutes is simply the average case.

You can see how long all other recent transactions have taken here: [http://bitcoinstats.org/ BitcoinStats.org].

[[Blocks]] (shown as "confirmations" in the GUI) are how the Bitcoin achieves consensus on who owns what. Once a block is found everyone agrees that you now own those coins, so you can spend them again. Until then it's possible that some network nodes believe otherwise, if somebody is attempting to defraud the system by reversing a transaction. The more confirmations a transaction has, the less risk there is of a reversal. Only 6 blocks or 1 hour is enough to make reversal computationally impractical. This is dramatically better than credit cards which can see chargebacks occur up to three months after the original transaction!

Ten minutes was specifically chosen by [[Satoshi]] as a tradeoff between propagation time of new blocks in large networks and the amount of work wasted due to chain splits. For a more technical explanation, see Satoshi's [http://www.bitcoin.org/bitcoin.pdf original technical paper].

[[File:TransactionConfirmationTimesExample.PNG]]

=== Do you have to wait until my transactions are confirmed in order to buy or sell things with Bitcoin? ===

YES, you do, IF the transaction is non-recourse. The Bitcoin reference software does not display transactions as confirmed until six blocks have passed (confirmations). As transactions are burred in the chain they become increasingly non-reversible but are very reversible before the first confirmation. Two to six confirmations are recommended for non-recourse situations depending on the value of the transactions involved.

When people ask this question they are usually thinking about applications like supermarkets. This generally is a recourse situation: if somebody tries to double-spend on a face-to-face transaction it might work a few times, but probabalistically speaking eventually one of the double-spends will get noticed, and the penalty for shoplifting charges in most localities is calibrated to be several times worse than the proceeds of a single shoplifting event.

Double-spends might be a concern for something like a snack machine in a low-traffic area with no nearby security cameras. Such a machine shouldn't honor 0-confirmation payments, and should instead use some other mechanism of clearing Bitcoin or validating transactions against reversal, see the wiki article [[Myths#Point_of_sale_with_bitcoins_isn.27t_possible_because_of_the_10_minute_wait_for_confirmation|here]] for alternatives.

When people ask this question they are usually thinking about applications that require immediate payment processing, like supermarkets or snack machines. Here is one way to reverse an unconfirmed payment:

A [[Double-spending#Finney_attack|Finney attack]], in which an attacker mines a block containing a movement of some coins back to themselves. Once they find a block solution, they quickly go to a merchant and make a purchase, then broadcast the block, thus taking back the coins. This attack is a risk primarily for goods that are dispatched immediately, like song downloads or currency trades. Because the attacker can't choose the time of the attack, it isn't a risk for merchants such as supermarkets where you can't choose exactly when to pay (due to queues, etc). The attack can fail if somebody else finds a block containing the purchasing transaction before you release your own block, therefore, merchants can reduce but not eliminate the risk by making purchasers wait some length of time that's less than a confirm.

Because pulling off this attack is not trivial, merchants who need to sell things automatically and instantly are most likely to just price the cost of reversal fraud in, or use insurance.

=== I was sent some bitcoins and they haven't arrived yet! Where are they? ===

Don't panic! There are a number of reasons why your bitcoins might not show up yet, and a number of ways to diagnose them.

The latest version of the Bitcoin-Qt client tells you how far it has yet to go in downloading the blockchain. Hover over the icon in the bottom right corner of the client to learn your client's status.

If it has not caught up then it's possible that your transaction hasn't been included in a block yet.

You can check pending transactions in the network by going [http://blockchain.info here] and then searching for your address. If the transaction is listed here then it's a matter of waiting until it gets included in a block before it will show in your client.

Bear in mind that if the transaction is based on a coin that was in a recent transaction then it could be considered a low priority transaction take longer to transfer if the transaction fee paid isn't high enough. Very low priority transactions with 0 fees might take hours or days to be included in a block.

=== Why does my Bitcoin address keep changing? ===

Whenever the address listed in "Your address" receives a transaction, Bitcoin replaces it with a new address. This is meant to encourage you to use a new address for every transaction, which enhances [[anonymity]]. All of your old addresses are still usable: you can see them in ''Settings -> Your Receiving Addresses''.

===How much will the transaction fee be?===

Some transactions might require a [[transaction fee]] for them to get confirmed in a timely manner. The transaction fee is processed by and received by the bitcoin miner. The most recent version of the Bitcoin client will estimate an appropriate fee when a fee might be required.

The fee is added to the payment amount. For example, if you are sending a 1.234 BTC payment and the client requires a 0.0005 BTC fee, then 1.2345 BTC will be subtracted from the wallet balance for the entire transaction and the address for where the payment was sent will receive a payment of 1.234 BTC.

In cases where a fee is required it is required because your transaction objectively looks like a denial of service attack to the bitcoin system, either due to it being burdensome to transmit or it recycles bitcoins you recently received. The wallet software attempts to avoid generating burdensome transactions, but it isn't always able if the funds in your wallet are new or are composed of many very tiny payments.

Because the fee is related to the amount of data that makes up the transaction and not to the amount of bitcoins being sent, the fee may seem extremely low (0.0005 BTC for a 1,000 BTC transfer) or unfairly high (0.004 BTC for a 0.02 BTC payment, or about 20%). If you are receiving tiny amounts (e.g., as small payments from a mining pool) then fees when sending will be higher than if your activity follows a more normal consumer or business transaction pattern. As of bitcoin 0.5.3 the required fee it will ask for will not be higher than 0.05 BTC, though for most users there is usually no required fee at all and 0.0005 is the most common when one is required.

=== What happens when someone sends me a bitcoin but my computer is powered off? ===

Bitcoins aren't actually "sent" to your wallet, the software only uses that term so that we can use the currency without having to learn new concepts. Your wallet is only needed when you wish to spend coins that you've received.

The coins that were sent to you when the client was not running will later appear as if they were received in your wallet when you later launch the client. It will download blocks and catch up with any transactions it didn't already have.

=== How long does "synchronizing" take when the Bitcoin client is first installed? What's it doing? ===

The popular Bitcoin client software from bitcoin.org implements a "full" Bitcoin node: It can carry out all the duties of the Bitcoin P2P system, it isn't simply a "client". One of the principles behind the operation of full Bitcoin nodes is that they don't assume that the other participants have followed the rules of the Bitcoin system. During synchronization, the software is processing historical Bitcoin transactions and making sure for itself that all of the rules of the system have been correctly followed.

In normal operation, after synchronizing, the software should use a hardly noticeable amount of IO, CPU, or network capacity.

The initial validation is very disk-IO-intensive, so the amount of time to synchronize depends on your disk speed and, to a lesser extent, your CPU speed. It can take anywhere from a few hours to a day or so. You can use the software while this process is going on, but you may not see recent payments to you until the synchronization has caught up to the point where those transactions happened.

If this is too long for you, you can download a pre-synchronized blockchain from [http://eu1.bitcoincharts.com/blockchain/ http://eu1.bitcoincharts.com/blockchain/]. Alternatively, you can try an alternative "lite" client such as Multibit or a super-light client like electrum, though these clients have somewhat weaker security, are less mature, and don't contribute to the health of the P2P network.

==Networking==
=== Do I need to configure my firewall to run bitcoin? ===

Bitcoin will connect to other nodes, usually on TCP port 8333. You will need to allow outgoing TCP connections to port 8333 if you want to allow your bitcoin client to connect to many nodes. [[Testnet]] uses TCP port 18333 instead of 8333.

If you want to restrict your firewall rules to a few IPs, you can find stable nodes in the [[Fallback Nodes|fallback nodes list]].

=== How does the peer finding mechanism work? ===

Bitcoin finds peers primarily by forwarding peer announcements within its own network and each node saves a database of peers that it's aware of, for future use. In order to bootstrap this process Bitcoin needs a list of initial peers, these can be provided manually but normally it obtains them by querying a set of DNS domain names which have automatically updated lists, if that doesn't work it falls back to a build-in list which is updated from time to time in new versions of the software. There is also an IRC based mechanism but it is disabled by default.

==Mining==
===What is mining?===
[[Mining]] is the process of spending computation power to secure Bitcoin transactions against reversal and introducing new Bitcoins to the system.

Technically speaking, mining is the calculation of a [[hash]] of the a block header, which includes among other things a reference to the previous block, a hash of a set of transactions and a [[nonce]]. If the hash value is found to be less than the current [[target]] (which is inversely proportional to the [[difficulty]]), a new block is formed and the miner gets the newly generated Bitcoins (50 per block at current levels). If the hash is not less than the current target, a new nonce is tried, and a new hash is calculated. This is done millions of times per second by each miner.

===Is mining used for some useful computation?===
The computations done when mining are internal to Bitcoin and not related to any other distributed computing projects. They serve the purpose of securing the Bitcoin network, which is useful.

===Is it not a waste of energy?===
Spending energy on creating and securing a free monetary system is hardly a waste. Also, services necessary for the operation of currently widespread monetary systems, such as banks and credit card companies, also spend energy, arguably more than Bitcoin would.

===Why don't we use calculations that are also useful for some other purpose?===
To provide security for the Bitcoin network, the calculations involved need to have some very specific features. These features are incompatible with leveraging the computation for other purposes.

===How can we stop miners from creating zero transaction blocks?===
The incentive for miners to include transactions is in the fees that come along with them. If we were to implement some minimum number of transactions per block it would be trivial for a miner to create and include transactions merely to surpass that threshold. As the network matures, the block reward drops, and miners become more dependent on transactions fees to pay their costs, the problem of zero transaction blocks should diminish over time.

===How does the proof-of-work system help secure Bitcoin?===
To give a general idea of the mining process, imagine this setup:

payload = <some data related to things happening on the Bitcoin network>
nonce = 1
hash = [http://en.wikipedia.org/wiki/SHA2 SHA2]( [http://en.wikipedia.org/wiki/SHA2 SHA2]( payload + nonce ) )

The work performed by a miner consists of repeatedly increasing "nonce" until
the hash function yields a value, that has the rare property of being below a certain
target threshold. (In other words: The hash "starts with a certain number of zeroes",
if you display it in the fixed-length representation, that is typically used.)

As can be seen, the mining process doesn't compute anything special. It merely
tries to find a number (also referred to as nonce) which - in combination with the payload -
results in a hash with special properties.

The advantage of using such a mechanism consists of the fact, that it is very easy to check a result: Given the payload and a specific nonce, only a single call of the hashing function is needed to verify that the hash has the required properties. Since there is no known way to find these hashes other than brute force, this can be used as a "proof of work" that someone invested a lot of computing power to find the correct nonce for this payload.

This feature is then used in the Bitcoin network to secure various aspects. An attacker
that wants to introduce malicious payload data into the network, will need to do the
required proof of work before it will be accepted. And as long as honest miners have more
computing power, they can always outpace an attacker.

Also see [http://en.wikipedia.org/wiki/SHA2 SHA2] and [http://en.wikipedia.org/wiki/Proof-of-work_system Proof-of-work system] on Wikipedia.

===Why was the "Generate coin" option of the client software removed?===

In the early days of Bitcoin, it was easy for anyone to find new blocks using standard CPUs. As more and more people started mining, the [[difficulty]] of finding new blocks has greatly increased to the point where the average time for a CPU to find a single block can be many years. The only cost-effective method of [[Mining|mining]] is using a high-end graphics card with special software (see also [[Why a GPU mines faster than a CPU]]) and/or joining a [[Bitcoin Pool|mining pool]]. Since solo CPU mining is essentially useless, it was removed from the GUI of the Bitcoin software.

==Security==

===Could miners collude to give themselves money or to fundamentally change the nature of Bitcoin?===

There are two questions in here. Let's look at them separately.

;Could miners gang up and give themselves money?

Mining itself is the process of creating new blocks in the block chain. Each block contains a list of all the transactions that have taken place across the entire Bitcoin network since the last block was created, as well as a hash of the previous block. New blocks are 'mined', or rather, generated, by Bitcoin clients correctly guessing sequences of characters in codes called 'hashes,' which are created using information from previous blocks. Bitcoin users may download specialized 'mining' software, which allows them to dedicate some amount of their processing power – however large or small – to guessing at strings within the hash of the previous block. Whoever makes the right guess first, thus creating a new block, receives a reward in Bitcoins.

The block chain is one of the two structures that makes Bitcoin secure, the other being the public-key encryption system on which Bitcoin trade is based. The block chain assures that not only is every single transaction that ever takes place recorded, but that every single transaction is recorded on the computer of anyone who chooses to store the relevant information. Many, many users have complete records of every transaction in Bitcoins history readily available to them at any point, and anyone who wants in the information can obtain it with ease. These things make Bitcoin very hard to fool.

The Bitcoin network takes considerable processing power to run, and since those with the most processing power can make the most guesses, those who put the most power toward to sustaining the network earn the most currency. Each correct guess yields, at present, fifty Bitcoins, and as Bitcoins are presently worth something (although the value still fluctuates) every miner who earns any number of Bitcoins makes money. Some miners pull in Bitcoins on their own; and some also join or form pools wherein all who contribute earn a share of the profits.

Therefore, first answer is a vehement “yes” – no only can miners collude to get more money, Bitcoin is designed to encourage them to do so. Bitcoin pools are communal affairs, and there is nothing dishonest or underhanded about them.

Of course, the real question is:

;Can they do so in ways not sanction by Bitcoin developers? Is there any way to rip off the network and make loads of money dishonestly?

Bitcoin isn't infallible. It can be cheated, but doing so is extremely difficult. Bitcoin was designed to evade some of the central problems with modern currencies – namely, that their trustworthiness hinges upon that of people who might not have users' best interests in mind. Every currency in the world (other than Bitcoin) is controlled by large institutions who keep track of what's done with done with it, and who can manipulate its value. And every other currency has value because people trust the institutions that control them.

Bitcoin doesn't ask that its users trust any institution. Its security is based on the cryptography that is an integral part of its structure, and that is readily available for any and all to see. Instead of one entity keeping track of transactions, the entire network does, so Bitcoins are astoundingly difficult to steal, or double-spend. Bitcoins are created in a regular and predictable fashion, and by many different users, so no one can decide to make a whole lot more and lessen their value. In short, Bitcoin is designed to be inflation-proof, double-spend-proof and completely distributed.

Nonetheless, there are a few ways that one can acquire Bitcoins dishonestly. Firstly, one can steal private keys. Key theft isn't something that Bitcoin security has been designed to prevent: it's up to users to keep theirs safe. But the cryptography is designed so that it is completely impossible to deduce someone's private from their public one. As long as you keep your private key to yourself, you don't have much to worry about. Furthermore, one could theoretically create a new block chain, but due to the way in which the block chain is constructed, this would be extremely difficult and require massive amounts of processing power. A full explanation of the difficulties involved can be found in the [[block chain]] article.

Bitcoin can be ripped off – but doing so would be extremely hard and require considerable expertise and a staggering amount of processing power. And it's only going to get harder with time. Bitcoin isn't impenetrable, but it's close enough to put any real worries in the peripherals.

;Could miners fundamentally change the nature of Bitcoin?

Once again, almost certainly not.

Bitcoin is a distributed network, so any changes implemented to the system must be accepted by all users. Someone trying to change the way Bitcoins are generated would have to convince every user to download and use their software – so the only changes that would go through are those that would be equally benefit all users.

And thus, it is more or less impossible for anyone to change the function of Bitcoin to their advantage. If users don't like the changes, they won't adopt them, whereas if users do like them, then these will help everyone equally. Of course, one can conceive of a situation where someone manages to get a change pushed through that provides them with an advantage that no one notices, but given that Bitcoin is structurally relatively simple, it is unlikely that any major changes will go through without someone noticing first.

The fact that such changes are so difficult to make testifies to the fully distributed nature of Bitcoin. Any centrally controlled currency can be modified by its central agency without the consent of its adherents. Bitcoin has no central authority, so it changes only at the behest of the whole community. Bitcoins development represents a kind of collective evolution; the first of its kind among currencies.

==Help==
===I'd like to learn more. Where can I get help?===

* Read the [[Introduction|introduction to bitcoin]]
* See the videos, podcasts, and blog posts from the [[Press]]
* Read and post on the [[Bitcoin:Community_portal#Bitcoin_Community_Forums|forums]]
* Chat on one of the [[Bitcoin:Community_portal#IRC_Chat|Bitcoin IRC]] channels
* Listen to [http://omegataupodcast.net/2011/03/59-bitcoin-a-digital-decentralized-currency/ this podcast], which goes into the details of how bitcoin works
* Ask questions on the [http://bitcoin.stackexchange.com Bitcoin Stack Exchange]

==See Also==

* [[Man page]]
* [[Introduction]]

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[[Category:Vocabulary]]

Help:FAQ

2012-10-25T15:19:10Z

Jepo: /* Does Bitcoin guarantee an influx of free money? */

Here you will find answers to the most commonly asked questions.

== General ==
=== What are bitcoins? ===
Bitcoins are the unit of currency of the Bitcoin system. A commonly used shorthand for this is “BTC” to refer to a price or amount (eg: “100 BTC”).
There are such things as [[physical bitcoins]], but ultimately, a bitcoin is just a number associated with a [[Address|Bitcoin Address]]. A physical bitcoin is simply an object, such as a coin, with the number carefully embedded inside. See also an [[Introduction|easy intro]] to bitcoin.

=== How can I get bitcoins? ===

There are a variety of ways to acquire bitcoins:

* Accept bitcoins as payment for goods or services.
* There are several services where you can [[buying bitcoins|trade them]] for traditional currency.
* Find someone to trade cash for bitcoins in-person through a [https://en.bitcoin.it/wiki/Category:Directories local directory].
* Participate in a [[Pooled mining|mining pool]].
* If you have a lot of mining hardware, you can solo mine and attempt to create a new [[block]] (currently yields 50 bitcoins).

===Does Bitcoin guarantee an influx of free money?===

Since Bitcoin is a new technology, what it is and how it works may be initially unclear. Bitcoin is sometimes presented as being one of three things:

'''A)''' Some sort of online 'get-rich-quick' scam.

'''B)''' A loophole in the market economy, the installation of which guarantees a steady influx of cash.

'''C)''' A sure investment that will almost certainly yield a profit.

In fact, none of the above are true. Let's look at them independently.

;Is Bitcoin a 'get-rich-quick' scheme?

If you've spent much time on the Internet, you've probably seen ads for many 'get-rich-quick' schemes. These ads usually promise huge profits for a small amounts of easy work. Such schemes are usually pyramid/matrix-style schemes that make money from their own employees and offer nothing of any real value. Most convince one to buy packages that will make them earn hundreds a day, which in fact have the buyer distribute more such ads, and make minute profits.

Bitcoin is in no way similar to these schemes. Bitcoin doesn't promise windfall profits. There is no way for the developers to make money from your involvement or to take money from you. That bitcoins are nearly impossible to acquire without the owner's consent represents one of its greatest strengths. Bitcoin is an experimental, virtual currency that may succeed or may fail. None of its developers expect to get rich off of it.

A more detailed answer to this question can be found [http://bitcointalk.org/?topic=7815.0 here].

;Will I make money by installing the client?

Most people who use Bitcoin don't earn anything by doing so, and the default client has no built-in way to earn Bitcoins. A small minority of people with dedicated, high-performance hardware do earn some Bitcoins by "''mining''" (generating new bitcoins) with special software, but joining Bitcoin shouldn't be construed as being the road to riches. Most Bitcoin users get involved because they find the project conceptually interesting and don't earn anything by doing so. This is also why you won't find much speculation about the political or economic repercussions of Bitcoin anywhere on this site: Bitcoin developers owe their dedication to the project's intellectual yieldings more than to those of a monetary nature. Bitcoin is still taking its first baby steps; it may go on to do great things but right now it only has something to offer those chasing conceptually interesting projects or bleeding edge technology.

;As an investment, is Bitcoin a sure thing?

Bitcoin is a new and interesting electronic currency, the value of which is not backed by any single government or organization. Like other currencies, it is worth something partly because people are willing to trade it for goods and services. Its exchange rate fluctuates continuously, and sometimes wildly. It lacks wide acceptance and is vulnerable to manipulation by parties with modest funding. Security incidents such as website and account compromise may trigger major sell-offs. Other fluctuations can build into positive feedback loops cause much larger exchange rate fluctuations. Anyone who puts money into Bitcoin should take measures to reduce their risk and consider it as a high-risk currency. Later, as Bitcoin becomes better known and more widely accepted, it should stabilize, but for the time being it is unpredictable. Any investment in Bitcoin should be done carefully and with a clear plan to manage risk.

=== Can I buy bitcoins with Paypal? ===

It is possible to buy [[physical bitcoins]] with PayPal but it is otherwise difficult and/or expensive to do so, because of significant risk to the seller.

While it is possible to find an individual who wishes to sell Bitcoin to you via Paypal, (perhaps via [http://www.bitcoin-otc.com/ #bitcoin-otc] ) most exchanges do not allow funding through PayPal. This is due to repeated cases where someone pays for bitcoins with Paypal receives their bitcoins, and then fraudulently complains to Paypal that they never received their purchase. PayPal often sides with the fraudulent buyer in this case which means any seller would need to cover that risk with higher fees or refuse to accept PayPal altogether.

Buying Bitcoins from individuals with this method is still possible, but requires the seller to have some trust that the buyer will not file a claim with PayPal to reverse the payment.

=== Where can I find a forum to discuss Bitcoin? ===

Please visit the [[Bitcoin:Community_portal#Bitcoin_Community_Forums_on_various_platforms|Community Portal]] for links to Bitcoin-related forums.

=== How are new bitcoins created? ===

[[File:total_bitcoins_over_time_graph.png|thumb|Number of bitcoins over time, assuming a perfect 10-minute interval.]]
New bitcoins are generated by the network through the process of mining. In a process that is similar to a continuous lottery, mining nodes on the network are awarded bitcoins each time they find the solution to a certain mathematical problem (and thereby create a new [[block]]). Creating a block is a [[proof of work]] with a difficulty that varies with the overall strength of the network. The reward for solving a block is [[Controlled Currency Supply|automatically adjusted]] so that in roughly the first four years of operation of the Bitcoin network, 10,500,000 BTC will be created. This amount is halved each four years, so it will be 5,250,000 over years 4-8, 2,625,000 over years 8-12 and so on. Thus the total number of bitcoins in existence will not exceed 21,000,000. See [[Controlled Currency Supply]].

Blocks are [[Mining|mined]] every 10 minutes, on average and for the first four years (210,000 blocks) each block includes 50 new bitcoins. As the amount of processing power directed at mining changes, the difficulty of creating new bitcoins changes. This difficulty factor is calculated every 2016 blocks and is based upon the time taken to generate the previous 2016 blocks. See [[Mining]].

=== What's the current total number of Bitcoins in existence? ===

[http://blockexplorer.com/q/totalbc Current count]. Also see [https://blockchain.info/charts/total-bitcoins Total Bitcoins in circulation chart]

The number of blocks times the coin value of a block is the number of coins in existence. The coin value of a block is 50 BTC for each of the first 210,000 blocks, 25 BTC for the next 210,000 blocks, then 12.5 BTC, 6.25 BTC and so on.

=== How divisible are Bitcoins? ===

A bitcoin can be divided down to 8 decimal places. Therefore, 0.00000001 BTC is the smallest amount that can be handled in a transaction. If necessary, the protocol and related software can be modified to handle even smaller amounts.

=== What do I call the various denominations of Bitcoins? ===

There is a lot of discussion about the naming of these fractions of Bitcoins. The leading candidates are:

* 1 BTC = 1 Bitcoin
* 0.01 BTC = 1 cBTC = 1 Centi-Bitcoin (also referred to as Bitcent)
* 0.001 BTC = 1 mBTC = 1 Milli-Bitcoin (also referred to as mbit (pronounced em-bit) or millibit or even bitmill)
* 0.000 001 BTC = 1 μBTC = 1 Micro-Bitcoin (also referred to as ubit (pronounced yu-bit) or microbit)

The above follows the accepted international SI prefixes for hundredths, thousandths, and millionths. There are many arguments against the special case of 0.01 BTC since it is unlikely to represent anything meaningful as the Bitcoin economy grows (it certainly won't be the equivalent of 0.01 USD, GBP or EUR). Equally, the inclusion of existing national currency denominations such as "cent", "nickel", "dime", "pence", "pound", "kopek" and so on are to be discouraged. This is a worldwide currency.

One exception is the "satoshi" which is smallest denomination currently possible

* 0.000 000 01 BTC = 1 Satoshi (pronounced sa-toh-shee)

which is so named in honour of Satoshi Nakamoto the pseudonym of the inventor of Bitcoin.

For an overview of all defined units of Bitcoin (including less common and niche units), see [[Units]].

Further discussion on this topic can be found on the forums here:

* [http://forum.bitcoin.org/index.php?topic=14438.msg195287#msg195287 We need names]
* [http://forum.bitcoin.org/index.php?topic=8282.0 What to call 0.001 BTC]

=== How does the halving work when the number gets really small? ===

Eventually the reward will go from 0.00000001 BTC to zero and no more bitcoins will be created.

The block reward calculation is done as a right bitwise shift of a 64-bit signed integer, which means it is divided by two and rounded down. The integer is equal to the value in BTC * 100,000,000 since internally in the reference client software, all Bitcoin balances and values are stored as unsigned integers.

With an initial block reward of 50 BTC, it will take many 4-year periods for the block reward to reach zero.

=== How long will it take to generate all the coins? ===

The last block that will generate coins will be block #6,929,999 which should be generated at or near the year 2140. The total number of coins in circulation will then remain static at 20,999,999.9769 BTC.

Even if the allowed precision is expanded from the current 8 decimals, the total BTC in circulation will always be slightly below 21 million (assuming everything else stays the same). For example, with 16 decimals of precision, the end total would be 20,999,999.999999999496 BTC.

=== If no more coins are going to be generated, will more blocks be created? ===

Absolutely! Even before the creation of coins ends, the use of [[transaction fee|transaction fees]] will likely make creating new blocks more valuable from the fees than the new coins being created. When coin generation ends, these fees will sustain the ability to use bitcoins and the Bitcoin network. There is no practical limit on the number of blocks that will be mined in the future.

=== But if no more coins are generated, what happens when Bitcoins are lost? Won't that be a problem? ===

Because of the law of supply and demand, when fewer bitcoins are available the ones that are left will be in higher demand, and therefore will have a higher value. So, as Bitcoins are lost, the remaining bitcoins will eventually increase in value to compensate. As the value of a bitcoin increases, the number of bitcoins required to purchase an item '''de'''creases. This is a [[Deflationary spiral|deflationary economic model]]. As the average transaction size reduces, transactions will probably be denominated in sub-units of a bitcoin such as millibitcoins ("Millies") or microbitcoins ("Mikes").

The Bitcoin protocol uses a base unit of one hundred-millionth of a Bitcoin ("a Satoshi"), but unused bits are available in the protocol fields that could be used to denote even smaller subdivisions.

=== If every transaction is broadcast via the network, does Bitcoin scale? ===
The Bitcoin protocol allows lightweight clients that can use Bitcoin without downloading the entire transaction history. As traffic grows and this becomes more critical, implementations of the concept will be developed. Full network nodes will at some point become a more specialized service.

With some modifications to the software, full Bitcoin nodes could easily keep up with both VISA and MasterCard combined, using only fairly modest hardware (a single high end server by todays standards). It is worth noting that the MasterCard network is structured somewhat like Bitcoin itself - as a peer to peer broadcast network.

Learn more about [[Scalability]].

==Economy==
=== Where does the value of Bitcoin stem from? What backs up Bitcoin? ===
Bitcoins have value because they are useful and because they are [[Controlled Currency Supply|scarce]]. As they are accepted by more merchants, their value will [http://en.wikipedia.org/wiki/Sticky_%28economics%29 stabilize]. See the [[Trade|list of Bitcoin-accepting sites]].

When we say that a currency is backed up by gold, we mean that there's a promise in place that you can exchange the currency for gold. Bitcoins, like dollars and euros, are not backed up by anything except the variety of merchants that accept them.

It's a common misconception that Bitcoins gain their value from the cost of electricity required to generate them. Cost doesn't equal value – hiring 1,000 men to shovel a big hole in the ground may be costly, but not valuable. Also, even though scarcity is a critical requirement for a useful currency, it alone doesn't make anything valuable. For example, your fingerprints are scarce, but that doesn't mean they have any exchange value.

=== Is Bitcoin a bubble? ===
Yes, in the same way as the euro and dollar are. They only have value in exchange and have no inherent value. If everyone suddenly stopped accepting your dollars, euros or bitcoins, the "bubble" would burst and their value would drop to zero. But that is unlikely to happen: even in Somalia, where the government collapsed 20 years ago, [http://en.wikipedia.org/wiki/Somali_shilling Somali shillings] are still accepted as payment.

=== Is Bitcoin a Ponzi scheme? ===
In a Ponzi Scheme, the founders persuade investors that they’ll profit. Bitcoin does not make such a guarantee. There is no central entity, just individuals building an economy.

A ponzi scheme is a zero sum game. Early adopters can only profit at the expense of late adopters. Bitcoin has possible win-win outcomes. Early adopters profit from the rise in value. Late adopters, and indeed, society as a whole, benefit from the usefulness of a stable, fast, inexpensive, and widely accepted p2p currency.

The fact that early adopters benefit more doesn't alone make anything a Ponzi scheme. All good investments in successful companies have this quality.

=== Doesn't Bitcoin unfairly benefit early adopters? ===
Early adopters have a large number of bitcoins now because they took a risk and invested resources in an unproven technology. By so doing, they have helped Bitcoin become what it is now and what it will be in the future (hopefully, a ubiquitous decentralized digital currency). It is only fair they will reap the benefits of their successful investment.

In any case, any bitcoin generated will probably change hands dozens of time as a medium of exchange, so the profit made from the initial distribution will be insignificant compared to the total commerce enabled by Bitcoin.

Since the pricing of Bitcoins has fallen greatly from its June 2011 peak, prices today are much more similar to those enjoyed by many early adopters. Those who are buying Bitcoins today likely believe that Bitcoin will grow significantly in the future. Setting aside the brief opportunity to have sold Bitcoins at the June 2011 peak enjoyed by few, the early-adopter window is arguably still open.

===Won't loss of wallets and the finite amount of Bitcoins create excessive deflation, destroying Bitcoin? ===
Worries about Bitcoin being destroyed by deflation are not entirely unfounded. Unlike most currencies, which experience inflation as their founding institutions create more and more units, Bitcoin will likely experience gradual deflation with the passage of time. Bitcoin is unique in that only a small amount of units will ever be produced (twenty-one million to be exact), this number has been known since the project's inception, and the units are created at a predicable rate.

Also, Bitcoin users are faced with a danger that doesn't threaten users of any other currency: if a Bitcoin user loses his wallet, his money is gone forever, unless he finds it again. And not just to him; it's gone completely out of circulation, rendered utterly inaccessible to anyone. As people will lose their wallets, the total number of Bitcoins will slowly decrease.

Therefore, Bitcoin seems to be faced with a unique problem. Whereas most currencies inflate over time, Bitcoin will mostly likely do the just the opposite. Time will see the irretrievable loss of an ever-increasing number of Bitcoins. An already small number will be permanently whittled down further and further. And as there become fewer and fewer Bitcoins, the laws of supply and demand suggest that their value will probably continually rise.

Thus Bitcoin is bound to once again stray into mysterious territory, because no one exactly knows what happens to a currency that grows continually more valuable. Economists generally agree that a low level of inflation is a good thing for a currency, but nobody is quite sure about what might happens to one that continually deflates. Although deflation could hardly be called a rare phenomenon, steady, constant deflation is unheard of. There may be a lot of speculation, no one has any hard data to back up their claims.

That being said, there is a mechanism in place to combat the obvious consequences. Extreme deflation would render most currencies highly impractical: if a single Canadian dollar could suddenly buy the holder a car, how would one go about buying bread or candy? Even pennies would fetch more than a person could carry. Bitcoin, however, offers a simple and stylish solution: infinite divisibility. Bitcoins can be divided up and trade into as small of pieces as one wants, so no matter how valuable Bitcoins become, one can trade them in practical quantities.

In fact, infinite divisibility should allow Bitcoins to function in cases of extreme wallet loss. Even if, in the far future, so many people have lost their wallets that only a single Bitcoin, or a fraction of one, remains, Bitcoin should continue to function just fine. No one can claim to be sure what is going to happen, but deflation may prove to present a smaller threat than many expect.

For more information, see the [[Deflationary spiral]] page.

=== What if someone bought up all the existing Bitcoins? ===
Bitcoin markets are competitive -- meaning the price of a bitcoin will rise or fall depending on supply and demand at certain price levels. Only a fraction of bitcoins issued to date are found on the exchange markets for sale. So even though technically a buyer with lots of money could buy all the bitcoins offered for sale, unless those holding the rest of the bitcoins offer them for sale as well, even the wealthiest, most determined buyer can't get at them.

Additionally, new currency continues to be issued daily and will continue to do so for decades though over time the rate at which they are issued declines to insignificant levels. Those who are mining aren't obligated to sell their bitcoins so not all bitcoins will make it to the markets even.

This situation doesn't suggest, however, that the markets aren't vulnerable to price manipulation. It doesn't take significant amounts of money to move the market price up or down and thus Bitcoin remains a volatile asset.

===What if someone creates a new block chain, or a new digital currency that renders Bitcoin obsolete?===

That the block chain cannot be easily forked represents one of the central security mechanisms of Bitcoin. Given the choice between two block chains, a Bitcoin miner always chooses the longer one - that is to say, the one with the more complex hash. Thusly, it ensures that each user can only spend their bitcoins once, and that no user gets ripped off.

As a consequence of the block chain structure, there may at any time be many different sub-branches, and the possibility always exists of a transaction being over-written by the longest branch, if it has been recorded in a shorter one. The older a transaction is though, the lower its chances of being over-written, and the higher of becoming permanent. Although the block chain prevents one from spending more Bitcoins than one has, it means that transactions can be accidentally nullified.

A new block chain would leave the network vulnerable to [[double-spending|double-spend]] attacks. However, the creation of a viable new chain presents considerable difficulty, and the possibility does not present much of a risk.

Bitcoin will always choose the longer Block Chain and determines the relative length of two branches by the complexities of their hashes. Since the hash of each new block is made from that of the block preceding it, to create a block with a more complex hash, one must be prepared to do more computation than has been done by the entire Bitcoin network from the fork point up to the newest of the blocks one is trying to supersede. Needless to say, such an undertaking would require a very large amount of processing power and since Bitcoin is continually growing and expanding, it will likely only require more with the passage of time.

A much more distinct and real threat to the Bitcoin use is the development of other, superior virtual currencies, which could supplant Bitcoin and render it obsolete and valueless.

A great deal of careful thought and ingenuity has gone into the development of Bitcoin, but it is the first of its breed, a prototype, and vulnerable to more highly-evolved competitors. At present, any threatening rivals have yet to rear its head; Bitcoin remains the first and foremost private virtual currency, but we can offer no guarantees that it will retain that position. It would certainly be in keeping with internet history for similar system built from the same principles to supersede and cast Bitcoin into obsolescence, after time had revealed its major shortcomings. Friendster and Myspace suffered similar fates at the hand of Facebook, Napster was ousted by Limeware, Bearshare and torrent applications, and Skype has all but crushed the last few disciples of the Microsoft Messenger army.

This may sound rather foreboding, so bear in mind that introduction of new and possibly better virtual currencies will not necessarily herald Bitcoin's demise. If Bitcoin establishes itself sufficiently firmly before the inception of the next generation of private, online currencies as to gain widespread acceptance and general stability, future currencies may pose little threat even if they can claim superior design.

==Sending and Receiving Payments==

=== Why do I have to wait 10 minutes before I can spend money I received? ===

10 minutes is the average time taken to find a block. It can be significantly more or less time than that depending on luck; 10 minutes is simply the average case.

You can see how long all other recent transactions have taken here: [http://bitcoinstats.org/ BitcoinStats.org].

[[Blocks]] (shown as "confirmations" in the GUI) are how the Bitcoin achieves consensus on who owns what. Once a block is found everyone agrees that you now own those coins, so you can spend them again. Until then it's possible that some network nodes believe otherwise, if somebody is attempting to defraud the system by reversing a transaction. The more confirmations a transaction has, the less risk there is of a reversal. Only 6 blocks or 1 hour is enough to make reversal computationally impractical. This is dramatically better than credit cards which can see chargebacks occur up to three months after the original transaction!

Ten minutes was specifically chosen by [[Satoshi]] as a tradeoff between propagation time of new blocks in large networks and the amount of work wasted due to chain splits. For a more technical explanation, see Satoshi's [http://www.bitcoin.org/bitcoin.pdf original technical paper].

[[File:TransactionConfirmationTimesExample.PNG]]

=== Do you have to wait until my transactions are confirmed in order to buy or sell things with Bitcoin? ===

YES, you do, IF the transaction is non-recourse. The Bitcoin reference software does not display transactions as confirmed until six blocks have passed (confirmations). As transactions are burred in the chain they become increasingly non-reversible but are very reversible before the first confirmation. Two to six confirmations are recommended for non-recourse situations depending on the value of the transactions involved.

When people ask this question they are usually thinking about applications like supermarkets. This generally is a recourse situation: if somebody tries to double-spend on a face-to-face transaction it might work a few times, but probabalistically speaking eventually one of the double-spends will get noticed, and the penalty for shoplifting charges in most localities is calibrated to be several times worse than the proceeds of a single shoplifting event.

Double-spends might be a concern for something like a snack machine in a low-traffic area with no nearby security cameras. Such a machine shouldn't honor 0-confirmation payments, and should instead use some other mechanism of clearing Bitcoin or validating transactions against reversal, see the wiki article [[Myths#Point_of_sale_with_bitcoins_isn.27t_possible_because_of_the_10_minute_wait_for_confirmation|here]] for alternatives.

When people ask this question they are usually thinking about applications that require immediate payment processing, like supermarkets or snack machines. Here is one way to reverse an unconfirmed payment:

A [[Double-spending#Finney_attack|Finney attack]], in which an attacker mines a block containing a movement of some coins back to themselves. Once they find a block solution, they quickly go to a merchant and make a purchase, then broadcast the block, thus taking back the coins. This attack is a risk primarily for goods that are dispatched immediately, like song downloads or currency trades. Because the attacker can't choose the time of the attack, it isn't a risk for merchants such as supermarkets where you can't choose exactly when to pay (due to queues, etc). The attack can fail if somebody else finds a block containing the purchasing transaction before you release your own block, therefore, merchants can reduce but not eliminate the risk by making purchasers wait some length of time that's less than a confirm.

Because pulling off this attack is not trivial, merchants who need to sell things automatically and instantly are most likely to just price the cost of reversal fraud in, or use insurance.

=== I was sent some bitcoins and they haven't arrived yet! Where are they? ===

Don't panic! There are a number of reasons why your bitcoins might not show up yet, and a number of ways to diagnose them.

The latest version of the Bitcoin-Qt client tells you how far it has yet to go in downloading the blockchain. Hover over the icon in the bottom right corner of the client to learn your client's status.

If it has not caught up then it's possible that your transaction hasn't been included in a block yet.

You can check pending transactions in the network by going [http://blockchain.info here] and then searching for your address. If the transaction is listed here then it's a matter of waiting until it gets included in a block before it will show in your client.

Bear in mind that if the transaction is based on a coin that was in a recent transaction then it could be considered a low priority transaction take longer to transfer if the transaction fee paid isn't high enough. Very low priority transactions with 0 fees might take hours or days to be included in a block.

=== Why does my Bitcoin address keep changing? ===

Whenever the address listed in "Your address" receives a transaction, Bitcoin replaces it with a new address. This is meant to encourage you to use a new address for every transaction, which enhances [[anonymity]]. All of your old addresses are still usable: you can see them in ''Settings -> Your Receiving Addresses''.

===How much will the transaction fee be?===

Some transactions might require a [[transaction fee]] for them to get confirmed in a timely manner. The transaction fee is processed by and received by the bitcoin miner. The most recent version of the Bitcoin client will estimate an appropriate fee when a fee might be required.

The fee is added to the payment amount. For example, if you are sending a 1.234 BTC payment and the client requires a 0.0005 BTC fee, then 1.2345 BTC will be subtracted from the wallet balance for the entire transaction and the address for where the payment was sent will receive a payment of 1.234 BTC.

In cases where a fee is required it is required because your transaction objectively looks like a denial of service attack to the bitcoin system, either due to it being burdensome to transmit or it recycles bitcoins you recently received. The wallet software attempts to avoid generating burdensome transactions, but it isn't always able if the funds in your wallet are new or are composed of many very tiny payments.

Because the fee is related to the amount of data that makes up the transaction and not to the amount of bitcoins being sent, the fee may seem extremely low (0.0005 BTC for a 1,000 BTC transfer) or unfairly high (0.004 BTC for a 0.02 BTC payment, or about 20%). If you are receiving tiny amounts (e.g., as small payments from a mining pool) then fees when sending will be higher than if your activity follows a more normal consumer or business transaction pattern. As of bitcoin 0.5.3 the required fee it will ask for will not be higher than 0.05 BTC, though for most users there is usually no required fee at all and 0.0005 is the most common when one is required.

=== What happens when someone sends me a bitcoin but my computer is powered off? ===

Bitcoins aren't actually "sent" to your wallet, the software only uses that term so that we can use the currency without having to learn new concepts. Your wallet is only needed when you wish to spend coins that you've received.

The coins that were sent to you when the client was not running will later appear as if they were received in your wallet when you later launch the client. It will download blocks and catch up with any transactions it didn't already have.

=== How long does "synchronizing" take when the bitcoin client is first installed? What is it doing? ===

The popular bitcoin client software from bitcoin.org implements a "full" bitcoin node: It can carry out all the duties of the bitcoin P2P system, it isn't simply a "client". One of the principles behind the operation of full bitcoin nodes is that they don't trust that the other participants have followed the rules of the bitcoin system. During synchronization the software is processing historical bitcoin transactions and making sure for itself that all of the rules of the system have been correctly followed.

In normal operation after synchronizing the software should use a hardly noticeable amount of IO, CPU, or network capacity.

The initial validation is very disk IO intensive so the amount of time to synchronize depend on your disk speed and, to a lesser extent, your cpu speed. It can take anywhere from a few hours to a day or so. You can use the software while this process is going on, but you may not see recent payments to you until the synchronization has caught up to the point where those transactions happened.

If this is too long for you, you can download a pre-synchronized blockchain from [http://eu1.bitcoincharts.com/blockchain/ http://eu1.bitcoincharts.com/blockchain/]. Alternatively, you can try an alternative "lite" client such as Multibit or a super-light client like electrum though these clients have somewhat weaker security, are less mature, and don't contribute to the health of the P2P network.

==Networking==
=== Do I need to configure my firewall to run bitcoin? ===

Bitcoin will connect to other nodes, usually on TCP port 8333. You will need to allow outgoing TCP connections to port 8333 if you want to allow your bitcoin client to connect to many nodes. [[Testnet]] uses TCP port 18333 instead of 8333.

If you want to restrict your firewall rules to a few IPs, you can find stable nodes in the [[Fallback Nodes|fallback nodes list]].

=== How does the peer finding mechanism work? ===

Bitcoin finds peers primarily by forwarding peer announcements within its own network and each node saves a database of peers that it's aware of, for future use. In order to bootstrap this process Bitcoin needs a list of initial peers, these can be provided manually but normally it obtains them by querying a set of DNS domain names which have automatically updated lists, if that doesn't work it falls back to a build-in list which is updated from time to time in new versions of the software. There is also an IRC based mechanism but it is disabled by default.

==Mining==
===What is mining?===
[[Mining]] is the process of spending computation power to secure Bitcoin transactions against reversal and introducing new Bitcoins to the system.

Technically speaking, mining is the calculation of a [[hash]] of the a block header, which includes among other things a reference to the previous block, a hash of a set of transactions and a [[nonce]]. If the hash value is found to be less than the current [[target]] (which is inversely proportional to the [[difficulty]]), a new block is formed and the miner gets the newly generated Bitcoins (50 per block at current levels). If the hash is not less than the current target, a new nonce is tried, and a new hash is calculated. This is done millions of times per second by each miner.

===Is mining used for some useful computation?===
The computations done when mining are internal to Bitcoin and not related to any other distributed computing projects. They serve the purpose of securing the Bitcoin network, which is useful.

===Is it not a waste of energy?===
Spending energy on creating and securing a free monetary system is hardly a waste. Also, services necessary for the operation of currently widespread monetary systems, such as banks and credit card companies, also spend energy, arguably more than Bitcoin would.

===Why don't we use calculations that are also useful for some other purpose?===
To provide security for the Bitcoin network, the calculations involved need to have some very specific features. These features are incompatible with leveraging the computation for other purposes.

===How can we stop miners from creating zero transaction blocks?===
The incentive for miners to include transactions is in the fees that come along with them. If we were to implement some minimum number of transactions per block it would be trivial for a miner to create and include transactions merely to surpass that threshold. As the network matures, the block reward drops, and miners become more dependent on transactions fees to pay their costs, the problem of zero transaction blocks should diminish over time.

===How does the proof-of-work system help secure Bitcoin?===
To give a general idea of the mining process, imagine this setup:

payload = <some data related to things happening on the Bitcoin network>
nonce = 1
hash = [http://en.wikipedia.org/wiki/SHA2 SHA2]( [http://en.wikipedia.org/wiki/SHA2 SHA2]( payload + nonce ) )

The work performed by a miner consists of repeatedly increasing "nonce" until
the hash function yields a value, that has the rare property of being below a certain
target threshold. (In other words: The hash "starts with a certain number of zeroes",
if you display it in the fixed-length representation, that is typically used.)

As can be seen, the mining process doesn't compute anything special. It merely
tries to find a number (also referred to as nonce) which - in combination with the payload -
results in a hash with special properties.

The advantage of using such a mechanism consists of the fact, that it is very easy to check a result: Given the payload and a specific nonce, only a single call of the hashing function is needed to verify that the hash has the required properties. Since there is no known way to find these hashes other than brute force, this can be used as a "proof of work" that someone invested a lot of computing power to find the correct nonce for this payload.

This feature is then used in the Bitcoin network to secure various aspects. An attacker
that wants to introduce malicious payload data into the network, will need to do the
required proof of work before it will be accepted. And as long as honest miners have more
computing power, they can always outpace an attacker.

Also see [http://en.wikipedia.org/wiki/SHA2 SHA2] and [http://en.wikipedia.org/wiki/Proof-of-work_system Proof-of-work system] on Wikipedia.

===Why was the "Generate coin" option of the client software removed?===

In the early days of Bitcoin, it was easy for anyone to find new blocks using standard CPUs. As more and more people started mining, the [[difficulty]] of finding new blocks has greatly increased to the point where the average time for a CPU to find a single block can be many years. The only cost-effective method of [[Mining|mining]] is using a high-end graphics card with special software (see also [[Why a GPU mines faster than a CPU]]) and/or joining a [[Bitcoin Pool|mining pool]]. Since solo CPU mining is essentially useless, it was removed from the GUI of the Bitcoin software.

==Security==

===Could miners collude to give themselves money or to fundamentally change the nature of Bitcoin?===

There are two questions in here. Let's look at them separately.

;Could miners gang up and give themselves money?

Mining itself is the process of creating new blocks in the block chain. Each block contains a list of all the transactions that have taken place across the entire Bitcoin network since the last block was created, as well as a hash of the previous block. New blocks are 'mined', or rather, generated, by Bitcoin clients correctly guessing sequences of characters in codes called 'hashes,' which are created using information from previous blocks. Bitcoin users may download specialized 'mining' software, which allows them to dedicate some amount of their processing power – however large or small – to guessing at strings within the hash of the previous block. Whoever makes the right guess first, thus creating a new block, receives a reward in Bitcoins.

The block chain is one of the two structures that makes Bitcoin secure, the other being the public-key encryption system on which Bitcoin trade is based. The block chain assures that not only is every single transaction that ever takes place recorded, but that every single transaction is recorded on the computer of anyone who chooses to store the relevant information. Many, many users have complete records of every transaction in Bitcoins history readily available to them at any point, and anyone who wants in the information can obtain it with ease. These things make Bitcoin very hard to fool.

The Bitcoin network takes considerable processing power to run, and since those with the most processing power can make the most guesses, those who put the most power toward to sustaining the network earn the most currency. Each correct guess yields, at present, fifty Bitcoins, and as Bitcoins are presently worth something (although the value still fluctuates) every miner who earns any number of Bitcoins makes money. Some miners pull in Bitcoins on their own; and some also join or form pools wherein all who contribute earn a share of the profits.

Therefore, first answer is a vehement “yes” – no only can miners collude to get more money, Bitcoin is designed to encourage them to do so. Bitcoin pools are communal affairs, and there is nothing dishonest or underhanded about them.

Of course, the real question is:

;Can they do so in ways not sanction by Bitcoin developers? Is there any way to rip off the network and make loads of money dishonestly?

Bitcoin isn't infallible. It can be cheated, but doing so is extremely difficult. Bitcoin was designed to evade some of the central problems with modern currencies – namely, that their trustworthiness hinges upon that of people who might not have users' best interests in mind. Every currency in the world (other than Bitcoin) is controlled by large institutions who keep track of what's done with done with it, and who can manipulate its value. And every other currency has value because people trust the institutions that control them.

Bitcoin doesn't ask that its users trust any institution. Its security is based on the cryptography that is an integral part of its structure, and that is readily available for any and all to see. Instead of one entity keeping track of transactions, the entire network does, so Bitcoins are astoundingly difficult to steal, or double-spend. Bitcoins are created in a regular and predictable fashion, and by many different users, so no one can decide to make a whole lot more and lessen their value. In short, Bitcoin is designed to be inflation-proof, double-spend-proof and completely distributed.

Nonetheless, there are a few ways that one can acquire Bitcoins dishonestly. Firstly, one can steal private keys. Key theft isn't something that Bitcoin security has been designed to prevent: it's up to users to keep theirs safe. But the cryptography is designed so that it is completely impossible to deduce someone's private from their public one. As long as you keep your private key to yourself, you don't have much to worry about. Furthermore, one could theoretically create a new block chain, but due to the way in which the block chain is constructed, this would be extremely difficult and require massive amounts of processing power. A full explanation of the difficulties involved can be found in the [[block chain]] article.

Bitcoin can be ripped off – but doing so would be extremely hard and require considerable expertise and a staggering amount of processing power. And it's only going to get harder with time. Bitcoin isn't impenetrable, but it's close enough to put any real worries in the peripherals.

;Could miners fundamentally change the nature of Bitcoin?

Once again, almost certainly not.

Bitcoin is a distributed network, so any changes implemented to the system must be accepted by all users. Someone trying to change the way Bitcoins are generated would have to convince every user to download and use their software – so the only changes that would go through are those that would be equally benefit all users.

And thus, it is more or less impossible for anyone to change the function of Bitcoin to their advantage. If users don't like the changes, they won't adopt them, whereas if users do like them, then these will help everyone equally. Of course, one can conceive of a situation where someone manages to get a change pushed through that provides them with an advantage that no one notices, but given that Bitcoin is structurally relatively simple, it is unlikely that any major changes will go through without someone noticing first.

The fact that such changes are so difficult to make testifies to the fully distributed nature of Bitcoin. Any centrally controlled currency can be modified by its central agency without the consent of its adherents. Bitcoin has no central authority, so it changes only at the behest of the whole community. Bitcoins development represents a kind of collective evolution; the first of its kind among currencies.

==Help==
===I'd like to learn more. Where can I get help?===

* Read the [[Introduction|introduction to bitcoin]]
* See the videos, podcasts, and blog posts from the [[Press]]
* Read and post on the [[Bitcoin:Community_portal#Bitcoin_Community_Forums|forums]]
* Chat on one of the [[Bitcoin:Community_portal#IRC_Chat|Bitcoin IRC]] channels
* Listen to [http://omegataupodcast.net/2011/03/59-bitcoin-a-digital-decentralized-currency/ this podcast], which goes into the details of how bitcoin works
* Ask questions on the [http://bitcoin.stackexchange.com Bitcoin Stack Exchange]

==See Also==

* [[Man page]]
* [[Introduction]]

[[de:FAQ]]
[[zh-cn:FAQ]]
[[fr:FAQ]]
[[ru:FAQ]]

[[Category:Technical]]
[[Category:Vocabulary]]

Help talk:Introduction

2012-10-25T04:17:46Z

Jepo: /* What's an EFT? */ new section

I would like to create this page, describing bitcoin in an easy manner.
---

"These bitcoins are valuable because they require the spending of real resources (CPU time and electricity) to produce,"

this seems to me the cost-theory of value, which is a fallacy. Digging holes in the ground requires spending of resources too.

--

Good page, but I was expecting a more concise introduction. Perhaps give it a more punchy, concise start?

--[[User:Mcnalu|Mcnalu]] 14:43, 15 May 2011 (GMT)

The idea for the "resources" talk was that people who spend CPU time and electricity to mine bitcoins will not want to simply give it away for free. The people who buy it from them later in exchange for something valuable also won't want to give it away cheaper, and so on. I think this kind of talk makes sense if you wish to promote Bitcoin because if you talk to people about it, basing its "worth" on how many people are already using it (how "useful" it is), you are conceding to Bitcoin's being subject to network effects, which, if it is, it is not going to survive. I hate to see great ideas like this going down because of stupid chicken-and-egg problems.

I suppose it's easy to present this all as useless electricity wasting, but at least it's based on something real. You spend this much electricity/CPU time, you get this many bitcoins. The alternative is the "good" old papers+guns system. What is that based on?

I haven't been following the arguments about the "gold standard" and whether it's "good" or "bad", and things like that. Haven't been in the forum much lately. Perhaps we could argue indefinitely about this. IMO, it's better for Bitcoin if the introduction talks about tangible things (maybe electricity isn't "tangible" but at least it's not dependent on people).

I'm going to change the phrase to talk about both the "usefulness" and the resources.

--[[User:Prcarter|Prcarter]] 06:29, 8 September 2011 (GMT)

This introduction shows Bitcoin's place and how it relates to the traditional banking system. It's to make people conscious of what is really going on and of the level of trust they are already placing on banks and those printed pieces of paper we base our survival on. I would hate a "buy bitcoins, they are cool"-type "promo".

--[[User:Prcarter|Prcarter]] 06:40, 8 September 2011 (GMT)

Yes, "maintaining account balances" tones it down a little.

--[[User:Prcarter|Prcarter]] 06:44, 8 September 2011 (GMT)

I had to change this back. Bitcoins do not have value because they take labor or electricity to create. See http://en.wikipedia.org/wiki/Labor_theory_of_value#The_relation_between_values_and_prices
While it is true that the value will tend to the cost of production, that is incidental.
--[[User:Atheros|Atheros]] 02:59, 25 October 2011 (GMT)

== it.bitcoin.it ==

I've started filling-in a few sections of the Italian version it.bitcoin.it. If you don't mind, I am using this page as the basis. So, I'm translating it and tightening it up at the same time. Would it be OK? I've also added a summary, using the bitcoin entry in wikipedia.

ciao

[[User:Gianco|Gianco]] 19:50, 16 June 2011 (GMT)

==Banking and Money, in general==

I am not sure about all the users of this site who are interested in and trying to understand BitCoin (as I am), but personally, I found myself, even quite recently, without an understanding about how banking and money works at all. The Khan Academy video series on banking and money was very helpful, I thought perhaps you might want to include a link in the Introduction and Basic Concepts. http://www.khanacademy.org/#banking-and-money
I think the more regular people can understand these basic things, the more they will be interested and engaged.

Thanks and great work so far it seems

[[User:Cruiser moves|Cruiser moves]] 12:44, 23 June 2011 (GMT)

== Confusion : how the Money is valued ==

The introduction is not upfront enough as to how Bitcoins get their value and why people are prepared to except them as money.ie We need on overview of the introduction to explain this without the explainations as to how they are created and cannot be duplicated. I gather what happens is that as long as there are enough people with things to sell and willing buyers then the money then gets its value due to its expanding usage.That is someone who has sold something can then turn around and buy something else with a bitcoin. Is that right?
And since the coins themselves are made scare by the design of their creation(time and energy) and their intrinsic unforgability (due to the mathematics) they then can be traded with confidence.Yes?

== What's an EFT? ==

--[[User:Jepo|Jepo]] ([[User talk:Jepo|talk]]) 04:17, 25 October 2012 (GMT)

Help:Introduction

2012-10-25T04:16:30Z

Jepo:

The purpose of this page is to provide a general overview of the Bitcoin system and economy.

==Basic Concepts==

===Currency===

Alice wants to buy the [http://www.grasshillalpacas.com/alpacaproductsforbitcoinoffer.html Alpaca socks] which Bob has for sale. In return, she is to provide something of equal value to Bob. The most efficient way to do this is by using a medium of exchange that Bob accepts which would be classified as currency. Currency makes trade easier by eliminating the need for [http://en.wikipedia.org/wiki/Coincidence_of_wants coincidence of wants] required in other systems of trade such as barter. Currency adoption and acceptance can be global, national, or in some cases local or community-based.

===Banks===

Alice needs not provide currency to Bob in-person. She may instead transfer this value by first entrusting her currency to a bank who promises to store and protect Alice's currency notes. The bank gives Alice a written promise (called a "bank statement") that entitles her to withdraw the same number of currency bills that she deposited. Since the money is still Alice's, she is entitled to do with it whatever she pleases, and the bank (like most banks), for a small fee, will do Alice the service of passing on the currency bills to Bob on her behalf. This is done by Alice's bank by giving the dollar bills to Bob's bank and informing them that the money is for Bob, who will then see the amount the next time he checks his balance or receives his bank statement.

Since banks have many customers, and bank employees require money for doing the job of talking to people and signing documents, banks in recent times have been using machines such as ATMs and web servers that do the job of interacting with customers instead of paid bank employees. The task of these machines is to learn what each customer wants to do with their money and, to the extent that it is possible, act on what the customer wants (for example, ATMs can hand out cash). Customers can always know how much money they have in their accounts, and they are confident that the numbers they see in their bank statements and on their computer screens accurately reflect the number of dollars that they can get from the bank on demand. They can be so sure of this that they can accept those numbers in the same way they accept paper banknotes (this is similar to the way people started accepting paper dollars when they had been accepting gold or silver).

Such a system has several disadvantages:
* It is costly. EFTs in Europe can cost 25 euros. Credit transactions can cost several percent of the transaction.
* It is slow. Checking and low cost wire services take days to complete.
* In most cases, it cannot be anonymous.
* Accounts can be frozen.
* Banks and other payment processors like PayPal, Visa, and Mastercard may refuse to process payments for legal entities.

Bitcoin is a system of owning and voluntarily transferring amounts of so-called ''bitcoins'', in a manner similar to an on-line banking, but pseudonymously and without reliance on a central authority to maintain account balances. If bitcoins are valuable, it is because they are useful and limited in supply.

==Bitcoin Basics==

===Creation of coins===
The creation of coins must be limited for the currency to have any value.

New coins are slowly [[Mining|mined]] into existence by following a mutually agreed-upon set of rules. A user [[Mining|mining]] bitcoins is running a software program that searches tirelessly for a solution to a very difficult math problem whose difficulty is precisely known. The difficulty is automatically adjusted regularly so that the number of solutions found globally, by everyone, is constant: an average of 6 per hour. When a solution is found, the user may tell everyone of the existence of this newly found solution, along with other information, packaged together in what is called a "[[Block|block]]".

Blocks contain 50 bitcoins at present. This amount, known as the block reward, is an incentive for people to perform the computation work required for generating blocks. Roughly every 4 years, the number of bitcoins that can be "mined" in a block reduces by 50%. Any block that is created by a malicious user that does not follow this rule (or any other rules) will be rejected by everyone else. In the end, no more than 21 million bitcoins will ever exist.

Because the block reward will decrease over the long term, miners will some day instead pay for their hardware and electricity costs by collecting [[Transaction_fee|transaction fees]]. The sender of money may voluntarily pay a small transaction fee which will be kept by whomever finds the next block. Paying this fee will encourage miners to include the transaction in a block more quickly.

===Sending payments===
To guarantee that a third-party, let's call her Eve, cannot spend other people's bitcoins by creating transactions in their names, Bitcoin uses [[Wikipedia:Public-key_cryptography|public key cryptography]] to make and verify digital signatures. In this system, each person, such as Alice or Bob, has one or more addresses each with an associated pair of public and private keys that they may hold in a [[Wallet|wallet]]. Only the user with the private key can sign a transaction to give some of their bitcoins to somebody else, but anyone can validate the signature using that user’s public key.

Suppose Alice wants to send a bitcoin to Bob.
* Bob sends his address (from which the public key can be derived) to Alice.
* Alice adds Bob’s public key and the amount of bitcoins to transfer to a message: a 'transaction' message.
* Alice signs the transaction with her private key.
* Alice broadcasts the transaction on the Bitcoin network for all to see.

(Only the first two steps require human action. The rest is done by the Bitcoin client software.)

Looking at this transaction from the outside, anyone who knows that these addresses belong to Alice and Bob can see that Alice has agreed to transfer the amount to Bob, because nobody else has Alice's private key. Alice would be foolish to give her private key to other people, as this would allow them to sign transactions in her name, removing funds from her control.

Later on, when Bob wishes to transfer the same bitcoins to Charley, he will do the same thing:
* Charlie sends Bob his address.
* Bob adds Charlie's public key and the amount of bitcoins to transfer to a message: a 'transaction' message.
* Bob signs the transaction with his private key.
* Bob broadcasts the transaction on the Bitcoin network for all to see.

Only Bob can do this because only he has the private key that can create a valid signature for the transaction.

Eve cannot change whose coins these are by replacing Bob’s public key with her public key, because Alice signed the transfer to Bob using her own private key, which is kept secret from Eve, and instructing that the coins which were hers now belong to Bob. So if Charlie accepts that the original coin was in the hands of Alice, he will also accept the fact that this coin was later passed to Bob, and now Bob is passing this same coin to him.

===Preventing [[double-spending]]===
The process described above does not prevent Alice from using the same bitcoins in more than one transaction. The following process does; this is the primary innovation behind Bitcoin.

* Details about the [[Transactions|transaction]] are [[Network|sent and forwarded]] to all or as many other computers as possible.
* A constantly growing chain of [[Blocks|blocks]] that contains a record of all transactions is collectively maintained by all computers (each has a full copy).
* To be accepted in the chain, transaction blocks must be valid and must include [[proof of work]] (one block generated by the network every 10 minutes).
* Blocks are chained in a way so that, if any one is modified, all following blocks will have to be recomputed.
* When multiple valid continuations to this chain appear, only the longest such branch is accepted and it is then extended further.

When Bob sees that his transaction has been included in a block, which has been made part of the single longest and fastest-growing block chain (extended with significant computational effort), he can be confident that the transaction by Alice has been accepted by the computers in the network and is permanently recorded, preventing Alice from creating a second transaction with the same coin. In order for Alice to thwart this system and double-spend her coins, she would need to muster more computing power than all other Bitcoin users combined.

===Anonymity===
When it comes to the Bitcoin network itself, there are no "accounts" to set up, and no e-mail addresses, user-names or passwords are required to hold or spend bitcoins. Each balance is simply associated with an address and its public-private key pair. The money "belongs" to anyone who has the private key and can sign transactions with it. Moreover, those keys do not have to be registered anywhere in advance, as they are only used when required for a transaction. Transacting parties do not need to know each other's identity in much the same way that a store owner does not know a cash-paying customer's name.

A [[Address|Bitcoin address]] mathematically corresponds to a public key and looks like this:

:1PC9aZC4hNX2rmmrt7uHTfYAS3hRbph4UN

Each person can have many such addresses, each with its own balance, which makes it very difficult to know which person owns what amount. In order to protect his [[Anonymity|privacy]], Bob can generate a new public-private key pair for each individual receiving transaction and the Bitcoin software encourages this behavior by default. Continuing the example from above, when Charlie receives the bitcoins from Bob, Charlie will not be able to identify who owned the bitcoins before Bob without further information.

===Capitalization / Nomenclature===
Since Bitcoin is both a currency and a protocol, capitalization of Bitcoin can be confusing. Generally accepted practice is to use Bitcoin (singular, with upper case letter b) to describe the protocol, network, and software, and bitcoin(s) (singular or plural, with lower case letter b) to describe actual bitcoins, as generated by computers. For example, you may have some bitcoins but when you run the program you are using Bitcoin.

==Where to see and explore==
You can directly explore the system in action by visiting [http://blockchain.info/ Blockchain.info] or [http://blockexplorer.com/ Bitcoin Block Explorer].
The site shows you the latest blocks in the block chain. The [[Block_chain|block chain]] contains the agreed history of all transactions that took place in the system.
Note how many blocks were generated in the last hour, which on average will be 6. Also notice the number of transactions and the total amount transferred in the last hour (last time I checked it was about 64 and 15K).
This should give you an indication of how active the system is.

Next, navigate to one of these blocks.
The block's [[hash]] begins with a run of zeros. This is what made creating the block so difficult; a hash that begins with many zeros is much more difficult to find than a hash with few or no zeros. The computer that generated this block had to try many ''Nonce'' values (also listed on the block's page) until it found one that generated this run of zeros.
Next, see the line titled ''Previous block''. Each block contains the hash of the block that came before it. This is what forms the chain of blocks.
Now take a look at all the transactions the block contains. The first transaction is the income earned by the computer that generated this block. It includes a fixed amount of coins created out of "thin air" and possibly a fee collected from other transactions in the same block.

Drill down into any of the transactions and you will see how it is made up of one or more amounts coming in and out.
Having more than one incoming and outgoing amount in a transaction enables the system to join and break amounts in any possible way, allowing for any fractional amount needed. Each incoming amount is a past transaction (which you can also view) from someone's address, and each outgoing amount is addressed to someone and will be part of a future transaction (which you can also navigate down into if it has already taken place.)

Finally you can follow any of the [[Address|addresses]] links and see what public information is available for them.

To get an impression of the amount of activity on the Bitcoin network, you might like to visit the monitoring websites [[Bitcoin Monitor]] and [[Bitcoin Watch]]. The first shows a real-time visualization of events on the Bitcoin network, and the second lists general statistics on the amount and size of recent transactions.

===How many people use Bitcoin?===

This is quite a difficult question to answer accurately. One approach is to count how many bitcoin clients connected to the network in the last 24 hours. We can do this because some clients transmit their addresses to the other members of the network periodically. In September 2011 this method suggested that there were about {{formatnum:60000}} users.

==See Also==

* [http://www.youtube.com/watch?v=Um63OQz3bjo What is Bitcoin?] video introduction
* Installing Bitcoin [[getting started]]
* [[How bitcoin works]]
* [[Using Bitcoin]]
* A gentle introduction to Bitcoin - [[BitcoinMe]]
* [http://coinlab.com/2011/12/bitcoin-primer Bitcoin Primer] from CoinLab
* Another introduction, ''The Rebooting Of Money'' podcast is found at [[Bitcoin Money]]
* A beginner's step-by-step guide to using Bitcoin, use of alternative wallets, and generally keeping your money and computer secure - [http://BitcoinIntro.com BitcoinIntro.com]
* [http://howtobitcoin.info howtobitcoin.info] Directory of bitcoin links for beginners

[[zh-cn:简介]]

[[de:Einführung]]

Help:FAQ

2012-10-25T03:42:40Z

Jepo:

Here you will find answers to the most commonly asked questions.

== General ==
=== What are bitcoins? ===
Bitcoins are the unit of currency of the Bitcoin system. A commonly used shorthand for this is “BTC” to refer to a price or amount (eg: “100 BTC”).
There are such things as [[physical bitcoins]], but ultimately, a bitcoin is just a number associated with a [[Address|Bitcoin Address]]. A physical bitcoin is simply an object, such as a coin, with the number carefully embedded inside. See also an [[Introduction|easy intro]] to bitcoin.

=== How can I get bitcoins? ===

There are a variety of ways to acquire bitcoins:

* Accept bitcoins as payment for goods or services.
* There are several services where you can [[buying bitcoins|trade them]] for traditional currency.
* Find someone to trade cash for bitcoins in-person through a [https://en.bitcoin.it/wiki/Category:Directories local directory].
* Participate in a [[Pooled mining|mining pool]].
* If you have a lot of mining hardware, you can solo mine and attempt to create a new [[block]] (currently yields 50 bitcoins).

===Does Bitcoin guarantee an influx of free money?===

Since Bitcoin is a new technology, what it is and how it works may be initially unclear. Bitcoin is sometimes presented as being one of three things:

'''A)''' Some sort of online 'get-rich-quick' scam.

'''B)''' A loophole in the market economy, the installation of which guarantees a steady influx of cash.

'''C)''' A sure investment that will almost certainly yield a profit.

In fact, none of the above are true. Let's look at them independently.

;Is Bitcoin a 'get-rich-quick' scheme?

If you've spent much time on the Internet, you've probably seen ads for many 'get-rich-quick' schemes. These ads usually promise huge profits for a small amounts of easy work. Such schemes are usually pyramid/matrix-style schemes that make money from their own employees and offer nothing of any real value. Most convince one to buy packages that will make them earn hundreds a day, which in fact have the buyer distribute more such ads, and make minute profits.

Bitcoin is in no way similar to these schemes. Bitcoin doesn't promise windfall profits. There is no way for the developers to make money from your involvement or to take money from you. That bitcoins are nearly impossible to acquire without the owner's consent represents one of its greatest strengths. Bitcoin is an experimental, virtual currency that may succeed or may fail. None of its developers expect to get rich off of it.

A more detailed answer to this question can be found [http://bitcointalk.org/?topic=7815.0 here].

;Will I make money by installing the client?

Most people who use Bitcoin don't earn anything by doing so, and the default client has no built-in way to earn Bitcoins. A small minority of people with dedicated, high-performance hardware do earn some Bitcoins by mining with special software but joining Bitcoin shouldn't be construed as being the road to riches. Most Bitcoin users get involved because they find the project conceptually interesting and don't earn anything by doing so. This is also why you won't find much speculation about the political or economic repercussions of Bitcoin anywhere on this site: Bitcoin developers owe their dedication to the project's intellectual yieldings more than to those of a monetary nature. Bitcoin is still taking its first baby steps; it may go on to do great things but right now it only has something to offer those chasing conceptually interesting projects or bleeding edge technology.

;As an investment, is Bitcoin a sure thing?

Bitcoin is a new and interesting electronic currency, the value of which is not backed by any single government or organization. Like other currencies it is worth something partly because people are willing to trade it for goods and services. Its exchange rate fluctuates continuously, and sometimes wildly. It lacks wide acceptance and is vulnerable to manipulation by parties with modest funding. Security incidents such as website and account compromise may trigger major sell-offs. Other fluctuations can build into positive feedback loops cause much larger exchange rate fluctuations. Anyone who puts money into Bitcoin should take measures to reduce their risk and consider it as a high-risk currency. Later, as Bitcoin becomes better known and more widely accepted, it should stabilize, but for the time being it is unpredictable. Any investment in Bitcoin should be done carefully and with a clear plan to manage risk.

=== Can I buy bitcoins with Paypal? ===

It is possible to buy [[physical bitcoins]] with PayPal but it is otherwise difficult and/or expensive to do so, because of significant risk to the seller.

While it is possible to find an individual who wishes to sell Bitcoin to you via Paypal, (perhaps via [http://www.bitcoin-otc.com/ #bitcoin-otc] ) most exchanges do not allow funding through PayPal. This is due to repeated cases where someone pays for bitcoins with Paypal receives their bitcoins, and then fraudulently complains to Paypal that they never received their purchase. PayPal often sides with the fraudulent buyer in this case which means any seller would need to cover that risk with higher fees or refuse to accept PayPal altogether.

Buying Bitcoins from individuals with this method is still possible, but requires the seller to have some trust that the buyer will not file a claim with PayPal to reverse the payment.

=== Where can I find a forum to discuss Bitcoin? ===

Please visit the [[Bitcoin:Community_portal#Bitcoin_Community_Forums_on_various_platforms|Community Portal]] for links to Bitcoin-related forums.

=== How are new bitcoins created? ===

[[File:total_bitcoins_over_time_graph.png|thumb|Number of bitcoins over time, assuming a perfect 10-minute interval.]]
New bitcoins are generated by the network through the process of mining. In a process that is similar to a continuous lottery, mining nodes on the network are awarded bitcoins each time they find the solution to a certain mathematical problem (and thereby create a new [[block]]). Creating a block is a [[proof of work]] with a difficulty that varies with the overall strength of the network. The reward for solving a block is [[Controlled Currency Supply|automatically adjusted]] so that in roughly the first four years of operation of the Bitcoin network, 10,500,000 BTC will be created. This amount is halved each four years, so it will be 5,250,000 over years 4-8, 2,625,000 over years 8-12 and so on. Thus the total number of bitcoins in existence will not exceed 21,000,000. See [[Controlled Currency Supply]].

Blocks are [[Mining|mined]] every 10 minutes, on average and for the first four years (210,000 blocks) each block includes 50 new bitcoins. As the amount of processing power directed at mining changes, the difficulty of creating new bitcoins changes. This difficulty factor is calculated every 2016 blocks and is based upon the time taken to generate the previous 2016 blocks. See [[Mining]].

=== What's the current total number of Bitcoins in existence? ===

[http://blockexplorer.com/q/totalbc Current count]. Also see [https://blockchain.info/charts/total-bitcoins Total Bitcoins in circulation chart]

The number of blocks times the coin value of a block is the number of coins in existence. The coin value of a block is 50 BTC for each of the first 210,000 blocks, 25 BTC for the next 210,000 blocks, then 12.5 BTC, 6.25 BTC and so on.

=== How divisible are Bitcoins? ===

A bitcoin can be divided down to 8 decimal places. Therefore, 0.00000001 BTC is the smallest amount that can be handled in a transaction. If necessary, the protocol and related software can be modified to handle even smaller amounts.

=== What do I call the various denominations of Bitcoins? ===

There is a lot of discussion about the naming of these fractions of Bitcoins. The leading candidates are:

* 1 BTC = 1 Bitcoin
* 0.01 BTC = 1 cBTC = 1 Centi-Bitcoin (also referred to as Bitcent)
* 0.001 BTC = 1 mBTC = 1 Milli-Bitcoin (also referred to as mbit (pronounced em-bit) or millibit or even bitmill)
* 0.000 001 BTC = 1 μBTC = 1 Micro-Bitcoin (also referred to as ubit (pronounced yu-bit) or microbit)

The above follows the accepted international SI prefixes for hundredths, thousandths, and millionths. There are many arguments against the special case of 0.01 BTC since it is unlikely to represent anything meaningful as the Bitcoin economy grows (it certainly won't be the equivalent of 0.01 USD, GBP or EUR). Equally, the inclusion of existing national currency denominations such as "cent", "nickel", "dime", "pence", "pound", "kopek" and so on are to be discouraged. This is a worldwide currency.

One exception is the "satoshi" which is smallest denomination currently possible

* 0.000 000 01 BTC = 1 Satoshi (pronounced sa-toh-shee)

which is so named in honour of Satoshi Nakamoto the pseudonym of the inventor of Bitcoin.

For an overview of all defined units of Bitcoin (including less common and niche units), see [[Units]].

Further discussion on this topic can be found on the forums here:

* [http://forum.bitcoin.org/index.php?topic=14438.msg195287#msg195287 We need names]
* [http://forum.bitcoin.org/index.php?topic=8282.0 What to call 0.001 BTC]

=== How does the halving work when the number gets really small? ===

Eventually the reward will go from 0.00000001 BTC to zero and no more bitcoins will be created.

The block reward calculation is done as a right bitwise shift of a 64-bit signed integer, which means it is divided by two and rounded down. The integer is equal to the value in BTC * 100,000,000 since internally in the reference client software, all Bitcoin balances and values are stored as unsigned integers.

With an initial block reward of 50 BTC, it will take many 4-year periods for the block reward to reach zero.

=== How long will it take to generate all the coins? ===

The last block that will generate coins will be block #6,929,999 which should be generated at or near the year 2140. The total number of coins in circulation will then remain static at 20,999,999.9769 BTC.

Even if the allowed precision is expanded from the current 8 decimals, the total BTC in circulation will always be slightly below 21 million (assuming everything else stays the same). For example, with 16 decimals of precision, the end total would be 20,999,999.999999999496 BTC.

=== If no more coins are going to be generated, will more blocks be created? ===

Absolutely! Even before the creation of coins ends, the use of [[transaction fee|transaction fees]] will likely make creating new blocks more valuable from the fees than the new coins being created. When coin generation ends, these fees will sustain the ability to use bitcoins and the Bitcoin network. There is no practical limit on the number of blocks that will be mined in the future.

=== But if no more coins are generated, what happens when Bitcoins are lost? Won't that be a problem? ===

Because of the law of supply and demand, when fewer bitcoins are available the ones that are left will be in higher demand, and therefore will have a higher value. So, as Bitcoins are lost, the remaining bitcoins will eventually increase in value to compensate. As the value of a bitcoin increases, the number of bitcoins required to purchase an item '''de'''creases. This is a [[Deflationary spiral|deflationary economic model]]. As the average transaction size reduces, transactions will probably be denominated in sub-units of a bitcoin such as millibitcoins ("Millies") or microbitcoins ("Mikes").

The Bitcoin protocol uses a base unit of one hundred-millionth of a Bitcoin ("a Satoshi"), but unused bits are available in the protocol fields that could be used to denote even smaller subdivisions.

=== If every transaction is broadcast via the network, does Bitcoin scale? ===
The Bitcoin protocol allows lightweight clients that can use Bitcoin without downloading the entire transaction history. As traffic grows and this becomes more critical, implementations of the concept will be developed. Full network nodes will at some point become a more specialized service.

With some modifications to the software, full Bitcoin nodes could easily keep up with both VISA and MasterCard combined, using only fairly modest hardware (a single high end server by todays standards). It is worth noting that the MasterCard network is structured somewhat like Bitcoin itself - as a peer to peer broadcast network.

Learn more about [[Scalability]].

==Economy==
=== Where does the value of Bitcoin stem from? What backs up Bitcoin? ===
Bitcoins have value because they are useful and because they are [[Controlled Currency Supply|scarce]]. As they are accepted by more merchants, their value will [http://en.wikipedia.org/wiki/Sticky_%28economics%29 stabilize]. See the [[Trade|list of Bitcoin-accepting sites]].

When we say that a currency is backed up by gold, we mean that there's a promise in place that you can exchange the currency for gold. Bitcoins, like dollars and euros, are not backed up by anything except the variety of merchants that accept them.

It's a common misconception that Bitcoins gain their value from the cost of electricity required to generate them. Cost doesn't equal value – hiring 1,000 men to shovel a big hole in the ground may be costly, but not valuable. Also, even though scarcity is a critical requirement for a useful currency, it alone doesn't make anything valuable. For example, your fingerprints are scarce, but that doesn't mean they have any exchange value.

=== Is Bitcoin a bubble? ===
Yes, in the same way as the euro and dollar are. They only have value in exchange and have no inherent value. If everyone suddenly stopped accepting your dollars, euros or bitcoins, the "bubble" would burst and their value would drop to zero. But that is unlikely to happen: even in Somalia, where the government collapsed 20 years ago, [http://en.wikipedia.org/wiki/Somali_shilling Somali shillings] are still accepted as payment.

=== Is Bitcoin a Ponzi scheme? ===
In a Ponzi Scheme, the founders persuade investors that they’ll profit. Bitcoin does not make such a guarantee. There is no central entity, just individuals building an economy.

A ponzi scheme is a zero sum game. Early adopters can only profit at the expense of late adopters. Bitcoin has possible win-win outcomes. Early adopters profit from the rise in value. Late adopters, and indeed, society as a whole, benefit from the usefulness of a stable, fast, inexpensive, and widely accepted p2p currency.

The fact that early adopters benefit more doesn't alone make anything a Ponzi scheme. All good investments in successful companies have this quality.

=== Doesn't Bitcoin unfairly benefit early adopters? ===
Early adopters have a large number of bitcoins now because they took a risk and invested resources in an unproven technology. By so doing, they have helped Bitcoin become what it is now and what it will be in the future (hopefully, a ubiquitous decentralized digital currency). It is only fair they will reap the benefits of their successful investment.

In any case, any bitcoin generated will probably change hands dozens of time as a medium of exchange, so the profit made from the initial distribution will be insignificant compared to the total commerce enabled by Bitcoin.

Since the pricing of Bitcoins has fallen greatly from its June 2011 peak, prices today are much more similar to those enjoyed by many early adopters. Those who are buying Bitcoins today likely believe that Bitcoin will grow significantly in the future. Setting aside the brief opportunity to have sold Bitcoins at the June 2011 peak enjoyed by few, the early-adopter window is arguably still open.

===Won't loss of wallets and the finite amount of Bitcoins create excessive deflation, destroying Bitcoin? ===
Worries about Bitcoin being destroyed by deflation are not entirely unfounded. Unlike most currencies, which experience inflation as their founding institutions create more and more units, Bitcoin will likely experience gradual deflation with the passage of time. Bitcoin is unique in that only a small amount of units will ever be produced (twenty-one million to be exact), this number has been known since the project's inception, and the units are created at a predicable rate.

Also, Bitcoin users are faced with a danger that doesn't threaten users of any other currency: if a Bitcoin user loses his wallet, his money is gone forever, unless he finds it again. And not just to him; it's gone completely out of circulation, rendered utterly inaccessible to anyone. As people will lose their wallets, the total number of Bitcoins will slowly decrease.

Therefore, Bitcoin seems to be faced with a unique problem. Whereas most currencies inflate over time, Bitcoin will mostly likely do the just the opposite. Time will see the irretrievable loss of an ever-increasing number of Bitcoins. An already small number will be permanently whittled down further and further. And as there become fewer and fewer Bitcoins, the laws of supply and demand suggest that their value will probably continually rise.

Thus Bitcoin is bound to once again stray into mysterious territory, because no one exactly knows what happens to a currency that grows continually more valuable. Economists generally agree that a low level of inflation is a good thing for a currency, but nobody is quite sure about what might happens to one that continually deflates. Although deflation could hardly be called a rare phenomenon, steady, constant deflation is unheard of. There may be a lot of speculation, no one has any hard data to back up their claims.

That being said, there is a mechanism in place to combat the obvious consequences. Extreme deflation would render most currencies highly impractical: if a single Canadian dollar could suddenly buy the holder a car, how would one go about buying bread or candy? Even pennies would fetch more than a person could carry. Bitcoin, however, offers a simple and stylish solution: infinite divisibility. Bitcoins can be divided up and trade into as small of pieces as one wants, so no matter how valuable Bitcoins become, one can trade them in practical quantities.

In fact, infinite divisibility should allow Bitcoins to function in cases of extreme wallet loss. Even if, in the far future, so many people have lost their wallets that only a single Bitcoin, or a fraction of one, remains, Bitcoin should continue to function just fine. No one can claim to be sure what is going to happen, but deflation may prove to present a smaller threat than many expect.

For more information, see the [[Deflationary spiral]] page.

=== What if someone bought up all the existing Bitcoins? ===
Bitcoin markets are competitive -- meaning the price of a bitcoin will rise or fall depending on supply and demand at certain price levels. Only a fraction of bitcoins issued to date are found on the exchange markets for sale. So even though technically a buyer with lots of money could buy all the bitcoins offered for sale, unless those holding the rest of the bitcoins offer them for sale as well, even the wealthiest, most determined buyer can't get at them.

Additionally, new currency continues to be issued daily and will continue to do so for decades though over time the rate at which they are issued declines to insignificant levels. Those who are mining aren't obligated to sell their bitcoins so not all bitcoins will make it to the markets even.

This situation doesn't suggest, however, that the markets aren't vulnerable to price manipulation. It doesn't take significant amounts of money to move the market price up or down and thus Bitcoin remains a volatile asset.

===What if someone creates a new block chain, or a new digital currency that renders Bitcoin obsolete?===

That the block chain cannot be easily forked represents one of the central security mechanisms of Bitcoin. Given the choice between two block chains, a Bitcoin miner always chooses the longer one - that is to say, the one with the more complex hash. Thusly, it ensures that each user can only spend their bitcoins once, and that no user gets ripped off.

As a consequence of the block chain structure, there may at any time be many different sub-branches, and the possibility always exists of a transaction being over-written by the longest branch, if it has been recorded in a shorter one. The older a transaction is though, the lower its chances of being over-written, and the higher of becoming permanent. Although the block chain prevents one from spending more Bitcoins than one has, it means that transactions can be accidentally nullified.

A new block chain would leave the network vulnerable to [[double-spending|double-spend]] attacks. However, the creation of a viable new chain presents considerable difficulty, and the possibility does not present much of a risk.

Bitcoin will always choose the longer Block Chain and determines the relative length of two branches by the complexities of their hashes. Since the hash of each new block is made from that of the block preceding it, to create a block with a more complex hash, one must be prepared to do more computation than has been done by the entire Bitcoin network from the fork point up to the newest of the blocks one is trying to supersede. Needless to say, such an undertaking would require a very large amount of processing power and since Bitcoin is continually growing and expanding, it will likely only require more with the passage of time.

A much more distinct and real threat to the Bitcoin use is the development of other, superior virtual currencies, which could supplant Bitcoin and render it obsolete and valueless.

A great deal of careful thought and ingenuity has gone into the development of Bitcoin, but it is the first of its breed, a prototype, and vulnerable to more highly-evolved competitors. At present, any threatening rivals have yet to rear its head; Bitcoin remains the first and foremost private virtual currency, but we can offer no guarantees that it will retain that position. It would certainly be in keeping with internet history for similar system built from the same principles to supersede and cast Bitcoin into obsolescence, after time had revealed its major shortcomings. Friendster and Myspace suffered similar fates at the hand of Facebook, Napster was ousted by Limeware, Bearshare and torrent applications, and Skype has all but crushed the last few disciples of the Microsoft Messenger army.

This may sound rather foreboding, so bear in mind that introduction of new and possibly better virtual currencies will not necessarily herald Bitcoin's demise. If Bitcoin establishes itself sufficiently firmly before the inception of the next generation of private, online currencies as to gain widespread acceptance and general stability, future currencies may pose little threat even if they can claim superior design.

==Sending and Receiving Payments==

=== Why do I have to wait 10 minutes before I can spend money I received? ===

10 minutes is the average time taken to find a block. It can be significantly more or less time than that depending on luck; 10 minutes is simply the average case.

You can see how long all other recent transactions have taken here: [http://bitcoinstats.org/ BitcoinStats.org].

[[Blocks]] (shown as "confirmations" in the GUI) are how the Bitcoin achieves consensus on who owns what. Once a block is found everyone agrees that you now own those coins, so you can spend them again. Until then it's possible that some network nodes believe otherwise, if somebody is attempting to defraud the system by reversing a transaction. The more confirmations a transaction has, the less risk there is of a reversal. Only 6 blocks or 1 hour is enough to make reversal computationally impractical. This is dramatically better than credit cards which can see chargebacks occur up to three months after the original transaction!

Ten minutes was specifically chosen by [[Satoshi]] as a tradeoff between propagation time of new blocks in large networks and the amount of work wasted due to chain splits. For a more technical explanation, see Satoshi's [http://www.bitcoin.org/bitcoin.pdf original technical paper].

[[File:TransactionConfirmationTimesExample.PNG]]

=== Do you have to wait until my transactions are confirmed in order to buy or sell things with Bitcoin? ===

YES, you do, IF the transaction is non-recourse. The Bitcoin reference software does not display transactions as confirmed until six blocks have passed (confirmations). As transactions are burred in the chain they become increasingly non-reversible but are very reversible before the first confirmation. Two to six confirmations are recommended for non-recourse situations depending on the value of the transactions involved.

When people ask this question they are usually thinking about applications like supermarkets. This generally is a recourse situation: if somebody tries to double-spend on a face-to-face transaction it might work a few times, but probabalistically speaking eventually one of the double-spends will get noticed, and the penalty for shoplifting charges in most localities is calibrated to be several times worse than the proceeds of a single shoplifting event.

Double-spends might be a concern for something like a snack machine in a low-traffic area with no nearby security cameras. Such a machine shouldn't honor 0-confirmation payments, and should instead use some other mechanism of clearing Bitcoin or validating transactions against reversal, see the wiki article [[Myths#Point_of_sale_with_bitcoins_isn.27t_possible_because_of_the_10_minute_wait_for_confirmation|here]] for alternatives.

When people ask this question they are usually thinking about applications that require immediate payment processing, like supermarkets or snack machines. Here is one way to reverse an unconfirmed payment:

A [[Double-spending#Finney_attack|Finney attack]], in which an attacker mines a block containing a movement of some coins back to themselves. Once they find a block solution, they quickly go to a merchant and make a purchase, then broadcast the block, thus taking back the coins. This attack is a risk primarily for goods that are dispatched immediately, like song downloads or currency trades. Because the attacker can't choose the time of the attack, it isn't a risk for merchants such as supermarkets where you can't choose exactly when to pay (due to queues, etc). The attack can fail if somebody else finds a block containing the purchasing transaction before you release your own block, therefore, merchants can reduce but not eliminate the risk by making purchasers wait some length of time that's less than a confirm.

Because pulling off this attack is not trivial, merchants who need to sell things automatically and instantly are most likely to just price the cost of reversal fraud in, or use insurance.

=== I was sent some bitcoins and they haven't arrived yet! Where are they? ===

Don't panic! There are a number of reasons why your bitcoins might not show up yet, and a number of ways to diagnose them.

The latest version of the Bitcoin-Qt client tells you how far it has yet to go in downloading the blockchain. Hover over the icon in the bottom right corner of the client to learn your client's status.

If it has not caught up then it's possible that your transaction hasn't been included in a block yet.

You can check pending transactions in the network by going [http://blockchain.info here] and then searching for your address. If the transaction is listed here then it's a matter of waiting until it gets included in a block before it will show in your client.

Bear in mind that if the transaction is based on a coin that was in a recent transaction then it could be considered a low priority transaction take longer to transfer if the transaction fee paid isn't high enough. Very low priority transactions with 0 fees might take hours or days to be included in a block.

=== Why does my Bitcoin address keep changing? ===

Whenever the address listed in "Your address" receives a transaction, Bitcoin replaces it with a new address. This is meant to encourage you to use a new address for every transaction, which enhances [[anonymity]]. All of your old addresses are still usable: you can see them in ''Settings -> Your Receiving Addresses''.

===How much will the transaction fee be?===

Some transactions might require a [[transaction fee]] for them to get confirmed in a timely manner. The transaction fee is processed by and received by the bitcoin miner. The most recent version of the Bitcoin client will estimate an appropriate fee when a fee might be required.

The fee is added to the payment amount. For example, if you are sending a 1.234 BTC payment and the client requires a 0.0005 BTC fee, then 1.2345 BTC will be subtracted from the wallet balance for the entire transaction and the address for where the payment was sent will receive a payment of 1.234 BTC.

In cases where a fee is required it is required because your transaction objectively looks like a denial of service attack to the bitcoin system, either due to it being burdensome to transmit or it recycles bitcoins you recently received. The wallet software attempts to avoid generating burdensome transactions, but it isn't always able if the funds in your wallet are new or are composed of many very tiny payments.

Because the fee is related to the amount of data that makes up the transaction and not to the amount of bitcoins being sent, the fee may seem extremely low (0.0005 BTC for a 1,000 BTC transfer) or unfairly high (0.004 BTC for a 0.02 BTC payment, or about 20%). If you are receiving tiny amounts (e.g., as small payments from a mining pool) then fees when sending will be higher than if your activity follows a more normal consumer or business transaction pattern. As of bitcoin 0.5.3 the required fee it will ask for will not be higher than 0.05 BTC, though for most users there is usually no required fee at all and 0.0005 is the most common when one is required.

=== What happens when someone sends me a bitcoin but my computer is powered off? ===

Bitcoins aren't actually "sent" to your wallet, the software only uses that term so that we can use the currency without having to learn new concepts. Your wallet is only needed when you wish to spend coins that you've received.

The coins that were sent to you when the client was not running will later appear as if they were received in your wallet when you later launch the client. It will download blocks and catch up with any transactions it didn't already have.

=== How long does "synchronizing" take when the bitcoin client is first installed? What is it doing? ===

The popular bitcoin client software from bitcoin.org implements a "full" bitcoin node: It can carry out all the duties of the bitcoin P2P system, it isn't simply a "client". One of the principles behind the operation of full bitcoin nodes is that they don't trust that the other participants have followed the rules of the bitcoin system. During synchronization the software is processing historical bitcoin transactions and making sure for itself that all of the rules of the system have been correctly followed.

In normal operation after synchronizing the software should use a hardly noticeable amount of IO, CPU, or network capacity.

The initial validation is very disk IO intensive so the amount of time to synchronize depend on your disk speed and, to a lesser extent, your cpu speed. It can take anywhere from a few hours to a day or so. You can use the software while this process is going on, but you may not see recent payments to you until the synchronization has caught up to the point where those transactions happened.

If this is too long for you, you can download a pre-synchronized blockchain from [http://eu1.bitcoincharts.com/blockchain/ http://eu1.bitcoincharts.com/blockchain/]. Alternatively, you can try an alternative "lite" client such as Multibit or a super-light client like electrum though these clients have somewhat weaker security, are less mature, and don't contribute to the health of the P2P network.

==Networking==
=== Do I need to configure my firewall to run bitcoin? ===

Bitcoin will connect to other nodes, usually on TCP port 8333. You will need to allow outgoing TCP connections to port 8333 if you want to allow your bitcoin client to connect to many nodes. [[Testnet]] uses TCP port 18333 instead of 8333.

If you want to restrict your firewall rules to a few IPs, you can find stable nodes in the [[Fallback Nodes|fallback nodes list]].

=== How does the peer finding mechanism work? ===

Bitcoin finds peers primarily by forwarding peer announcements within its own network and each node saves a database of peers that it's aware of, for future use. In order to bootstrap this process Bitcoin needs a list of initial peers, these can be provided manually but normally it obtains them by querying a set of DNS domain names which have automatically updated lists, if that doesn't work it falls back to a build-in list which is updated from time to time in new versions of the software. There is also an IRC based mechanism but it is disabled by default.

==Mining==
===What is mining?===
[[Mining]] is the process of spending computation power to secure Bitcoin transactions against reversal and introducing new Bitcoins to the system.

Technically speaking, mining is the calculation of a [[hash]] of the a block header, which includes among other things a reference to the previous block, a hash of a set of transactions and a [[nonce]]. If the hash value is found to be less than the current [[target]] (which is inversely proportional to the [[difficulty]]), a new block is formed and the miner gets the newly generated Bitcoins (50 per block at current levels). If the hash is not less than the current target, a new nonce is tried, and a new hash is calculated. This is done millions of times per second by each miner.

===Is mining used for some useful computation?===
The computations done when mining are internal to Bitcoin and not related to any other distributed computing projects. They serve the purpose of securing the Bitcoin network, which is useful.

===Is it not a waste of energy?===
Spending energy on creating and securing a free monetary system is hardly a waste. Also, services necessary for the operation of currently widespread monetary systems, such as banks and credit card companies, also spend energy, arguably more than Bitcoin would.

===Why don't we use calculations that are also useful for some other purpose?===
To provide security for the Bitcoin network, the calculations involved need to have some very specific features. These features are incompatible with leveraging the computation for other purposes.

===How can we stop miners from creating zero transaction blocks?===
The incentive for miners to include transactions is in the fees that come along with them. If we were to implement some minimum number of transactions per block it would be trivial for a miner to create and include transactions merely to surpass that threshold. As the network matures, the block reward drops, and miners become more dependent on transactions fees to pay their costs, the problem of zero transaction blocks should diminish over time.

===How does the proof-of-work system help secure Bitcoin?===
To give a general idea of the mining process, imagine this setup:

payload = <some data related to things happening on the Bitcoin network>
nonce = 1
hash = [http://en.wikipedia.org/wiki/SHA2 SHA2]( [http://en.wikipedia.org/wiki/SHA2 SHA2]( payload + nonce ) )

The work performed by a miner consists of repeatedly increasing "nonce" until
the hash function yields a value, that has the rare property of being below a certain
target threshold. (In other words: The hash "starts with a certain number of zeroes",
if you display it in the fixed-length representation, that is typically used.)

As can be seen, the mining process doesn't compute anything special. It merely
tries to find a number (also referred to as nonce) which - in combination with the payload -
results in a hash with special properties.

The advantage of using such a mechanism consists of the fact, that it is very easy to check a result: Given the payload and a specific nonce, only a single call of the hashing function is needed to verify that the hash has the required properties. Since there is no known way to find these hashes other than brute force, this can be used as a "proof of work" that someone invested a lot of computing power to find the correct nonce for this payload.

This feature is then used in the Bitcoin network to secure various aspects. An attacker
that wants to introduce malicious payload data into the network, will need to do the
required proof of work before it will be accepted. And as long as honest miners have more
computing power, they can always outpace an attacker.

Also see [http://en.wikipedia.org/wiki/SHA2 SHA2] and [http://en.wikipedia.org/wiki/Proof-of-work_system Proof-of-work system] on Wikipedia.

===Why was the "Generate coin" option of the client software removed?===

In the early days of Bitcoin, it was easy for anyone to find new blocks using standard CPUs. As more and more people started mining, the [[difficulty]] of finding new blocks has greatly increased to the point where the average time for a CPU to find a single block can be many years. The only cost-effective method of [[Mining|mining]] is using a high-end graphics card with special software (see also [[Why a GPU mines faster than a CPU]]) and/or joining a [[Bitcoin Pool|mining pool]]. Since solo CPU mining is essentially useless, it was removed from the GUI of the Bitcoin software.

==Security==

===Could miners collude to give themselves money or to fundamentally change the nature of Bitcoin?===

There are two questions in here. Let's look at them separately.

;Could miners gang up and give themselves money?

Mining itself is the process of creating new blocks in the block chain. Each block contains a list of all the transactions that have taken place across the entire Bitcoin network since the last block was created, as well as a hash of the previous block. New blocks are 'mined', or rather, generated, by Bitcoin clients correctly guessing sequences of characters in codes called 'hashes,' which are created using information from previous blocks. Bitcoin users may download specialized 'mining' software, which allows them to dedicate some amount of their processing power – however large or small – to guessing at strings within the hash of the previous block. Whoever makes the right guess first, thus creating a new block, receives a reward in Bitcoins.

The block chain is one of the two structures that makes Bitcoin secure, the other being the public-key encryption system on which Bitcoin trade is based. The block chain assures that not only is every single transaction that ever takes place recorded, but that every single transaction is recorded on the computer of anyone who chooses to store the relevant information. Many, many users have complete records of every transaction in Bitcoins history readily available to them at any point, and anyone who wants in the information can obtain it with ease. These things make Bitcoin very hard to fool.

The Bitcoin network takes considerable processing power to run, and since those with the most processing power can make the most guesses, those who put the most power toward to sustaining the network earn the most currency. Each correct guess yields, at present, fifty Bitcoins, and as Bitcoins are presently worth something (although the value still fluctuates) every miner who earns any number of Bitcoins makes money. Some miners pull in Bitcoins on their own; and some also join or form pools wherein all who contribute earn a share of the profits.

Therefore, first answer is a vehement “yes” – no only can miners collude to get more money, Bitcoin is designed to encourage them to do so. Bitcoin pools are communal affairs, and there is nothing dishonest or underhanded about them.

Of course, the real question is:

;Can they do so in ways not sanction by Bitcoin developers? Is there any way to rip off the network and make loads of money dishonestly?

Bitcoin isn't infallible. It can be cheated, but doing so is extremely difficult. Bitcoin was designed to evade some of the central problems with modern currencies – namely, that their trustworthiness hinges upon that of people who might not have users' best interests in mind. Every currency in the world (other than Bitcoin) is controlled by large institutions who keep track of what's done with done with it, and who can manipulate its value. And every other currency has value because people trust the institutions that control them.

Bitcoin doesn't ask that its users trust any institution. Its security is based on the cryptography that is an integral part of its structure, and that is readily available for any and all to see. Instead of one entity keeping track of transactions, the entire network does, so Bitcoins are astoundingly difficult to steal, or double-spend. Bitcoins are created in a regular and predictable fashion, and by many different users, so no one can decide to make a whole lot more and lessen their value. In short, Bitcoin is designed to be inflation-proof, double-spend-proof and completely distributed.

Nonetheless, there are a few ways that one can acquire Bitcoins dishonestly. Firstly, one can steal private keys. Key theft isn't something that Bitcoin security has been designed to prevent: it's up to users to keep theirs safe. But the cryptography is designed so that it is completely impossible to deduce someone's private from their public one. As long as you keep your private key to yourself, you don't have much to worry about. Furthermore, one could theoretically create a new block chain, but due to the way in which the block chain is constructed, this would be extremely difficult and require massive amounts of processing power. A full explanation of the difficulties involved can be found in the [[block chain]] article.

Bitcoin can be ripped off – but doing so would be extremely hard and require considerable expertise and a staggering amount of processing power. And it's only going to get harder with time. Bitcoin isn't impenetrable, but it's close enough to put any real worries in the peripherals.

;Could miners fundamentally change the nature of Bitcoin?

Once again, almost certainly not.

Bitcoin is a distributed network, so any changes implemented to the system must be accepted by all users. Someone trying to change the way Bitcoins are generated would have to convince every user to download and use their software – so the only changes that would go through are those that would be equally benefit all users.

And thus, it is more or less impossible for anyone to change the function of Bitcoin to their advantage. If users don't like the changes, they won't adopt them, whereas if users do like them, then these will help everyone equally. Of course, one can conceive of a situation where someone manages to get a change pushed through that provides them with an advantage that no one notices, but given that Bitcoin is structurally relatively simple, it is unlikely that any major changes will go through without someone noticing first.

The fact that such changes are so difficult to make testifies to the fully distributed nature of Bitcoin. Any centrally controlled currency can be modified by its central agency without the consent of its adherents. Bitcoin has no central authority, so it changes only at the behest of the whole community. Bitcoins development represents a kind of collective evolution; the first of its kind among currencies.

==Help==
===I'd like to learn more. Where can I get help?===

* Read the [[Introduction|introduction to bitcoin]]
* See the videos, podcasts, and blog posts from the [[Press]]
* Read and post on the [[Bitcoin:Community_portal#Bitcoin_Community_Forums|forums]]
* Chat on one of the [[Bitcoin:Community_portal#IRC_Chat|Bitcoin IRC]] channels
* Listen to [http://omegataupodcast.net/2011/03/59-bitcoin-a-digital-decentralized-currency/ this podcast], which goes into the details of how bitcoin works
* Ask questions on the [http://bitcoin.stackexchange.com Bitcoin Stack Exchange]

==See Also==

* [[Man page]]
* [[Introduction]]

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