Bitcoin Wiki - User contributions [en]

Bridgewalker

2013-10-03T18:45:06Z

Jav: Added to Android category

Bridgewalker is a euro-denominated wallet for Android. It allows sending and receiving of bitcoins, but does so by exchanging back and forth to Euros on the fly.

Feature Overview:
* Send and receive Bitcoins using QR codes or Bitcoin URIs
* Sharing of Bitcoin address via standard Android share function
* Support for [[Green address|green addresses]]
* One-click registration

This project was announced on March 23, 2013<ref>[https://bitcointalk.org/index.php?topic=156943.0 Bridgewalker now in public beta]</ref>.

==External Links==

* [https://www.bridgewalkerapp.com/ Bridgewalker] website
* [https://play.google.com/store/apps/details?id=com.bridgewalkerapp.androidclient Bridgewalker] on Google Play

==References==
<references />

[[Category:Mobile]]
[[Category:Frontends]]
[[Category:User Interfaces]]
[[Category:Clients]]
[[Category:Wallets]]
[[Category:EWallets]]
[[Category:Android]]

Software

2013-10-03T18:43:52Z

Jav: Added Bridgewalker to the Android section

List of Bitcoin-related '''software'''. See also [[:Category:Software|Category:Software]].

Be sure to keep on top of the latest [[CVEs|security vulnerabilities]]!

==Bitcoin clients==
===Bitcoin clients===
::''Main article and feature comparison: [[Clients]]''
*[[Bitcoin-Qt]] - C++/Qt based tabbed UI. Linux/MacOSX/Windows. Full-featured [[Thin Client Security|thick client]] that downloads the entire [[block chain]], using code from the original Bitcoin client.
*[[bitcoind]] - GUI-less version of the original Bitcoin client, providing a [[API reference (JSON-RPC)|JSON-RPC]] interface
*[[MultiBit]] - lightweight [[Thin Client Security|thin client]] for Windows, MacOS and Linux with support for opening multiple wallets simultaneously
*[[Electrum]] - a "blazing fast, open-source, multi-OS Bitcoin client/wallet with a very active community" - also a [[Thin Client Security|thin client]].
*[[Bitcoin-js-remote]] - JavaScript RPC client, support for QR codes
*[https://github.com/TheSeven/Bitcoin-WebUI Bitcoin WebUI] - JavaScript RPC client
*[https://github.com/zamgo/bitcoin-webskin Bitcoin Webskin] - PHP web interface to bitcoind and namecoind
*[https://bitcointalk.org/index.php?topic=50721.0 subvertx] - command line bitcoin tools
*[[Bitcoiner]] - Java RPC client (Android)
*[[Armory]] - Python-based client currently an alpha-level release, the beta version is being crowdfunded
*[[Spesmilo]] - Python/PySide RPC client (abandoned)
*[[Gocoin]] - GUI-less client node written in Go language, with a separate cold deterministic wallet app.

====Frontends to eWallet====
*[[BitPay]] - Android application
*[https://blockchain.info/wallet Blockchain] - Javascript bitcoin client with client side encryption.

====Experimental====
*[[Freecoin]] - C++ client, supports alternative currencies like [https://bitcointalk.org/index.php?topic=9493.0 Beertoken]
*[[BitDroid]] - Java client
*[[Bitdollar]] - C++/Qt client, unstable beta version

===Libraries===
*[https://bitcointalk.org/index.php?topic=30646.0 libbitcoin]
*[[BitCoinJ]] - Java client library, early development stage but used in live projects already
*[[BCCAPI]] (Bitcoin Client API) - a java library designed for making secure light-weight bitcoin clients.

==Bitcoin Trade Data==
*[[Bitcoin Charts]] – Prices, volume, and extensive charting on virtually all Bitcoin markets.
*[[MtGox Live]] - An innovative chart showing a live feed of [[MtGox]] trades and market depth. (Must Use Chrome)
*[http://btccharts.com BTCCharts] - An innovative chart showing a live feed of multiple markets, currencies and timeframes.
*[http://MY-BTC.info MY-BTC.INFO] - A free profit/loss portfolio manager for Bitcoins and other digital currencies including many charts.
*[http://BitcoinExchangeRate.org BitcoinExchangeRate.org] - Bitcoin and USD converter with convenient URL scheme and Auto-updating Portfolio Spreadsheet.
*[[Bitcoin Sentiment Index]] - A financial index that collects and disseminates sentiment data about bitcoin.
*[[Preev]] - Bitcoin converter with live exchange rates.
*[[Skami]] - Bitcoin Market Exchange comparison charts.
*[[BitcoinSentiment]] - Crowdvoting site offering means of voting and viewing voters sentiment towards bitcoin.
*[[TradingView]] – network where traders exchange ideas about Bitcoin using advanced free online charts

==Bitcoin software==

===Web interfaces for merchants===
*[[BitMerch]] - Embeddable HTML buttons, instant sign-up, instant payouts, automatic price adjustment for other currencies. No programming skills required to set up.
*[[BTCMerch]] - 0.5% transaction fee. Buyers stay on the merchant's site.
*[[Bitcoin Evolution]] - Non wallet-based Buy Now button to insert into websites (handles sales tracking; client must be used for actual transaction)
*[[BitPay]] - Buy Now buttons, Checkout posts/callbacks, Mobile Checkout, JSON API
*[[Btceconomy]] - a JavaScript widget listing items for sale
*[[Javascript Bitcoin Converter]] - currency conversion
*[[WalletBit]] - Easy JavaScript Buy Now buttons, Instant Payment Notification, Application Programming Interface (JSON API), Mobile Checkout, QR-Code
* [https://PikaPay.com PikaPay] ([[PikaPay|info]]) Buy Now buttons, Twitter Integration, JSON API

===Shopping Cart Integration in eCommerce-Systems===
*[[Zen Cart Bitcoin Payment Module]] - a payment module that interacts with bitcoind for the Zen Cart eCommerce shopping chart.
*[[Karsha Shopping Cart Interface]] - is a mobile payment-interface which enables its users to accept payments.
*[[Bitcoin-Cash]] - an easy to use payment module for xt:Commerce
*[[BitPay]] - bitcoin plugins for Magento, Opencart, Zencart, PHP, JSON API
*[[WalletBit]] - Plugins for PrestaShop, OpenCart, PHP, JSON API
*[[OpenCart Bitcoin]] - An OpenCart payment module that communicates with a bitcoin client using JSON RPC.
*[[OsCommerce_Bitcoin_Payment_Module|OsCommerce Bitcoin Payment Module]] - a payment module that uses a python monitoring script to interact with bitcoind for OsCommerce
* [http://drupal.org/project/uc_bitcoin Drupal Ubercart Bitcoin payment method] enables you to accept Bitcoin as payment for your Drupal/Ubercart enabled website product/services.

=== Enterprise server ===
*[http://bitsofproof.com Bits of Proof] - a modular enterprise-ready implementation of the Bitcoin protocol.

===Web apps (opensource)===
*[[Bitcoin Central]] - currency exchange
*[[Bitcoin Poker Room]] - poker site
*[[Abe]] - block chain viewer
*[[Simplecoin]] - PHP web frontend for a pool
*[[bitcoin_simple_php_tools]] simple php tools for webmasters

===Browser extensions===
*[[Bitcoin Extension]] - check balance and send bitcoins (Chrome)
*[[Bitcoin Prices (extension)]] - monitoring price (Firefox)
*[[Bitcoin Ticker]] - monitoring price (Chrome)
*[[Biticker]] - Bitcoin ticker, currency converter and history price graph (Chrome)
*[https://chrome.google.com/webstore/detail/bitcoin-microformats/bkanicejfbhlidgjkpenmddnacjengld?hl=en Bitcoin Microformats] Show bitcoin address metadata embedded in a page (Chrome)
*[https://chrome.google.com/webstore/detail/bitcoin-address-lookup/pmlblkdmadbidammhjiponepngbfcpge?hl=en Bitcoin Address Lookup] Right click an address to view its value. (Chrome)

===PC apps===
*[https://sourceforge.net/projects/bitcointrader/ Qt Bitcoin Trader] - Open Source Mt.Gox, BTC-e and Bitstamp trading client for Windows, Mac OS X and Linux
*[[http://www.mybtc-trader.com MyBTC-Trader.com]] - a MtGox Bitcoin trading client for windows with GUI
*[[Mining Explorer]] - monitoring tool for bitcoin mining
*[[Bitcoin SMS Alert]] - sends SMS text alerts to a user's phone based on BTC price / percent thresholds.
*[[BTConvert]] - currency conversion
*[[Sierra Chart MtGox Bridge]] - real-time charting
*[[BitTicker]] - monitoring price (Mac OS X)
*[[ToyTrader]] - a command line trading tool for [[MtGox]]
*[[goxsh]] - a command-line frontend to the [[MtGox|Mt. Gox Bitcoin Exchange]] (Python)
*[[MyBitcoins gadget]] - monitoring pool earnings / price (Windows gadget)
*[[Bitcoin QR Popup]] - streamlined interface to bitcoin for POS systems (Windows)
*[http://gnome-help.org/content/show.php/Bitcoin+Rate?content=138572 Bitcoin Rate] - Desktop widget with BTC exchange rate (KDE)
*[http://kde-apps.org/content/show.php?content=142344 Bitcoin Monitor] - Desktop widget to monitor status of your Bitcoin miners on mining pools (KDE)

===Mobile apps===
==== iPhone / iPad ====
*[https://blockchain.info/wallet/iphone-app Blockchain] - Fully featured iphone bitcoin app.
*[[Bitcoin Ticker (iPhone)]] - monitoring price w/push notifications
*[[BitCoins Mobile]] - First iPad native app! Live market data, news feeds, mining pool statistics, full screen exchange price charts, bitcoin network statistical charts. (iPad only, iPhone/iPod Touch coming soon!)
*[https://github.com/teeman/BitcoinTrader BitcoinTrader] - Spend/receive BTC via QR codes, trade, deposit/withdraw, etc. Supports Mt. Gox, TradeHill, ExchB, CampBX, and InstaWallet.
*[[Bit-pay]] - Mobile Checkout, set prices in any currency and receive mobile-to-mobile payment
*[[Easywallet.org]] - Web based wallet, works with QR Code scanner on iPhone/iPad/iPod touch
*[https://itunes.apple.com/us/app/btc-miner/id648411895?ls=1&mt=8 BTC Miner (iPhone)] - monitor mining results from various mining pools on iPhone/iPad/iPod touch

==== Android ====
* Direct link to Android Market bitcoin apps. https://play.google.com/store/search?q=bitcoin
*[[BitCare]] - Track bitcoin wallet balance, trade on Mt.Gox, monitor mining pool hashrate, balance, worker status.
*[[Bitcoin Alert]] - monitoring price (Android)
*[[Bitcoin-android]] - Does not appear to be being maitained anymore. https://market.android.com/details?id=com.bitcoinandroid
*[[Bitcoin Wallet Balance]] - view your balance in real time on your android phone
*[[Bitcoin Wallet]] - This is the most functional Android bitcoin wallet application. https://market.android.com/details?id=de.schildbach.wallet
*[[BitcoinSpinner]] - Single address, easy to use, lightweight and open source client. Keys stored on device.
*[[BitcoinX]] - monitoring price (Android)
*[[BitPay]] - https://market.android.com/details?id=com.bitcoin.bitpay (Is not related to the bit-pay.com online payment processor.)
*[[Bridgewalker]] - euro-denominated wallet for the Bitcoin economy
*[https://blockchain.info/wallet/android-app Blockchain] - Lightweight Android Bitcoin Client - Also works with blockchain.info web interface and iphone app.
*[[http://coincliff.com CoinCliff]] - Monitors price and fires alarms to wake you up, or notifications, as in text messages (Android)
*[[Easywallet.org]] - Web based wallet, works with QR Code scanner on Android devices
*[[Miner Status]] - monitoring miner status (Android)
*[[SMS Bitcoins]] - transactions by SMS

==== Windows Phone 7 ====
*Direct link to Windows Phone Marketplace Bitcoin apps: [http://www.windowsphone.com/en-us/store/search?q=bitcoin]

see also [[Bitcoin Payment Apps]]

===Operating systems===
*[[MinePeon]] - Bitcoin mining on the Raspberry PI
*BAMT - a minimal Linux based OS intended for headless mining. Initially announced [https://bitcointalk.org/index.php?topic=65915.0 here] (not maintained)
*[[LinuxCoin]] - a lightweight Debian-based OS, with the Bitcoin client and GPU mining software (not maintained)

===Mining apps===
Main page: [[Mining software]]
*[[50Miner]] - A GUI frontend for Windows(Poclbm, Phoenix, DiabloMiner, cgminer)
*[[BFGMiner]] - Modular ASIC/FPGA/GPU miner in C
*[[BTCMiner]] - Bitcoin Miner for ZTEX FPGA Boards
*[[Bit Moose]] - Run Miners as a Windows Service.
*[[Poclbm]] - Python/OpenCL GPU miner ([[Poclbm-gui|GUI(Windows & MacOS X)]])
*[[CGMiner]] - ASIC/FPGA/GPU miner in C
*[[Poclbm-mod]] - more efficient version of [[Poclbm]] ([[Poclbm-mod-gui|GUI]])
*[[DiabloMiner]] - Java/OpenCL GPU miner ([[DiabloMiner.app|MAC OS X GUI]])
*[[RPC Miner]] - remote RPC miner ([[RPCminer.app|MAC OS X GUI]])
*[[Phoenix miner]] - miner
*[[Cpu Miner]] - miner
*[[Ufasoft miner]] - miner
*[[Pyminer]] - Python miner, reference implementation
*[[Remote miner]] - mining pool software
*[[Open Source FGPA Bitcoin Miner]] - a miner that makes use of an FPGA Board
*[https://github.com/mkburza/Flash-Player-Bitcoin-Miner Flash Player Bitcoin Miner] - A proof of concept Adobe Flash Player miner
*[http://fabulouspanda.co.uk/macminer/ MacMiner] - A native Mac OS X Bitcoin/Litecoin miner based on cgminer, bfgminer, cpuminer and poclbm
*[[Asteroid]] - Mac-specific GUI based on cgminer
*[[MultiMiner]] - GUI based on cgminer/bfgminer for Windows, OS X and Linux, allows switching between currencies based on profitability

===Mining Pool Servers (backend)===
Main page: [[Poolservers]]

*[[ecoinpool]] - Erlang poolserver (not maintained)
*[[Eloipool]] - Fast Python3 poolserver
*[[Pushpoold]] - Old mining poolserver in C (not maintained)
*[[Poold]] - Old Python mining poolserver (not maintained)
*[[PoolServerJ]] - Java mining poolserver (not maintained)

===Utilities, libraries, and interfaces:===
*[[BitcoinCrypto]] - a lightweight Bitcoin crypto library for Java/Android
*[[Bitcoin Dissector]] - a wireshark dissector for the bitcoin protocol
*[[Bitcointools]] - a set of Python tools accessing the transaction database and the wallet
*[[Finance::MtGox]] - a Perl module which interfaces with the Mt. Gox API
*[[libblkmaker]] - C library implementation of [[getblocktemplate]] decentralized mining protocol
*[[python-blkmaker]] - Python module implementation of [[getblocktemplate]] decentralized mining protocol

===Lists of software===
*[[BitGit]] - list of Bitcoin-related opensource projects hosted at Git

===Developer resources===
*[[:Category:Developer|Category:Developer]]
*[[:Category:Technical|Category:Technical]]
*[[Original Bitcoin client/API calls list]]
*[[API reference (JSON-RPC)]]
*[[PHP_developer_intro|PHP Developer Introduction]]

===Other===
*[[Namecoin]] - a distributed naming system based on Bitcoin technology
*[[Bitcoin Consultancy]] - an organization providing open source software and Bitcoin-related consulting
*[[Open Transactions]] - a financial crypto and digital cash software library, complementary to Bitcoin
*[[Moneychanger]] - Java-based GUI for [[Open Transactions]]
*[http://btcnames.org/ BTCnames] - a webbased aliasing service which allows to handle unlimited names for your BTC deposit hashes
*[[Devcoin]] - the open source developer coin

[[Category:Software|*]]

Mobile Payment Apps

2013-10-03T18:40:30Z

Jav: Added Bridgewalker to list

List of Mobile apps used for payments.

{| class = "wikitable"|
|-
| App || Android || iPhone || Nokia || BlackBerry || QR-code || NFC || Btc Storage || OpenSource || Last Active || Comments
|-
| [[Bitcoin Wallet|Bitcoin Wallet for Android/BB10]] || {{Table Value Yes}} || {{Table Value No}} || {{Table Value No}} || {{Table Value Yes}} || {{Table Value Yes}} || {{Table Value Yes}} || On Phone + encrypted backup || [https://github.com/schildbach/bitcoin-wallet Github] [https://code.google.com/p/bitcoin-wallet/ Google] || 2013-Jan-28 || [https://bitcointalk.org/index.php?board=100.0 Forum]
|-
| [[BitcoinApp]] || {{Table Value No}} || {{Table Value Yes}} || {{Table Value No}} || {{Table Value No}} || ? || ? || On Phone || [https://github.com/udibr/bitcoinApp Github] || 2011-May-18
|-
| [[BitPay]] || {{Table Value Yes}} || {{Table Value No}} || ? || ? || {{Table Value Yes}} || {{Table Value No}} || [[Instawallet]] || [https://github.com/warpi/BitPay Github] || 2011-Sep-26
|-
| [[Bitcoin Express]] || {{Table Value No}} || {{Table Value Yes}} || {{Table Value No}} || {{Table Value No}} || ? || ? || ? || [https://github.com/fingster/BTC-Express Github] || 2011-Jul-24 || [http://bitcointalk.org/index.php?topic=31362.0 Forum]
|-
| [[BitcoinSpinner]] || {{Table Value Yes}} || {{Table Value No}} || {{Table Value No}} || {{Table Value No}} || {{Table Value Yes}} || {{Table Value No}} || On Phone, chain on server || [http://code.google.com/p/bitcoinspinner/ Google] || 2011-12-01 || [http://bitcointalk.org/index.php?topic=52674.0 Forum]
|-
| [[BlockChain.info|Blockchain for iPhone]] || {{Table Value No}} || {{Table Value Yes}}<ref>Cydia / Jailbroken only.</ref> || {{Table Value No}} || {{Table Value No}} || {{Table Value Yes}} || {{Table Value No}} || On Phone, encrypted backup on server || [https://github.com/zootreeves/My-Wallet-iPhone GitHub] || 2012-05-12 || [http://bitcointalk.org/index.php?topic=75673.0 Forum]
|-
| [[BlockChain.info|Blockchain for Android]] || {{Table Value Yes}} || {{Table Value No}} || {{Table Value No}} || {{Table Value No}} || {{Table Value Yes}} || {{Table Value No}} || On Phone, encrypted backup on server || [https://github.com/zootreeves/My-Wallet-Android Github] || 2012-05-12 || [http://bitcointalk.org/index.php?topic=74191.0 Forum]
|-
| [[Bridgewalker]] || {{Table Value Yes}} || {{Table Value No}} || {{Table Value No}} || {{Table Value No}} || {{Table Value Yes}} || {{Table Value No}} || Not applicable, balance is in Euros || Proprietary || 2013-10-03 || [https://bitcointalk.org/index.php?topic=156943.0 Forum]
|-
| [[Instawallet]] || {{Table Value Yes}} || {{Table Value No}} || ? || ? || {{Table Value No}} || {{Table Value No}} || [[Instawallet]] || Proprietary || 2012-06-18 || [https://bitcointalk.org/index.php?topic=73388.msg972384#msg972384 Forum]
|-
| [[FriendlyPay]] || {{Table Value No}} || {{Table Value Yes}} || {{Table Value No}} || {{Table Value No}} || {{Table Value Yes}} || {{Table Value No}} || [[Instawallet]] || Proprietary || 2012-05-12 || [http://bitcointalk.org/index.php?topic=6785.msg869671#msg869671 Forum]
|-
| [[Paytunia]] || {{Table Value Yes}} || {{Table Value Yes}}<ref>Private Beta</ref> || ? || ? || {{Table Value Yes}} || {{Table Value No}} || Server (Hosted) || Proprietary || 2012-05-12 || [http://bitcointalk.org/index.php?topic=75550.0 Forum]
|-
| [[Easywallet.org]] || {{Table Value Yes}} || {{Table Value Yes}} || ? || ? || {{Table Value Yes}} || {{Table Value No}} || Easywallet.org || Proprietary || 2012-05-12 || [https://bitcointalk.org/index.php?topic=75665.0 Forum]
|-
| [[ResponsePay]] || {{Table Value Yes}} || {{Table Value Yes}} || {{Table Value No}} || {{Table Value No}} || {{Table Value Yes}} || {{Table Value No}} || ResponsePay.com || Proprietary || 2012-07-10 || [https://bitcointalk.org/index.php?topic=91431.0 Forum]
|}

==See Also==

* [[Payment methods]]
* [http://dre.tx0.org/compare.htm Open-Source Bitcoin Clients for the Desktop]

==References==
<references />

[[Category:Mobile]]
[[Category:Software]]
[[Category:Clients]]
[[Category:Wallets]]
[[Category:Free Software]]
[[Category:Open Source]]

Bridgewalker

2013-10-03T18:35:05Z

Jav: Created page for the Bridgewalker Bitcoin wallet

Green address

2013-06-09T21:20:41Z

Jav: Add Bridgewalker to list

A '''green address''' is a special trusted [[Bitcoin address]] that is used to indicate the origin of funds to a recipient. Assuming the recipient trusts the owner of the address to not attempt a [[Double-spending|double spend]], the recipient may treat the funds as confirmed the moment they arrive.

As an example, assume website Z accepts incoming Bitcoin payments, but also trusts the green address published by [[Mt. Gox]]. Customer C wants to withdraw funds from Mt. Gox and send them to a payment address of website Z. A customer who does a withdrawal from Mt. Gox can click the ''use green address'' checkbox, which will result in the payment being sent to the green address as an intermediate step before forwarding the payment to site Z. Site Z can confirm that the payment passed through Mt. Gox's green address and trust the payment as confirmed immediately, since it knows that the only party who could potentially perform an attack to reverse the payment is Mt. Gox, which is presumed unlikely.

The concept originated on the forums and was discussed in two threads<ref>https://bitcointalk.org/index.php?topic=48170</ref><ref>https://bitcointalk.org/index.php?topic=32818.0</ref>. Since then, it has been implemented by [[Instawallet]] and [[Mt. Gox]].

==See Also==

* [http://bitcoin.stackexchange.com/questions/1730/what-are-green-addresses/1731#1731 What Are Green Addresses] Q&A on StackExchange

==External Links==
===Sites that allow withdrawals from green addresses===
* [https://mtgox.com MtGox ]
* [[Instawallet]]
* [https://www.bridgewalkerapp.com/ Bridgewalker Bitcoin Wallet]

===Sites that recognize green addresses===
* [[Btctip|BTCTip]]
* [[BTCPak]]
* [[Instawallet]]
* [https://www.bridgewalkerapp.com/ Bridgewalker Bitcoin Wallet]

==References==
<references/>

Green address

2013-06-09T21:20:22Z

Jav: Add Bridgewalker to list

Green address

2013-06-09T21:17:34Z

Jav: Remove dead link to www.GreenAddress.org

A '''green address''' is a special trusted [[Bitcoin address]] that is used to indicate the origin of funds to a recipient. Assuming the recipient trusts the owner of the address to not attempt a [[Double-spending|double spend]], the recipient may treat the funds as confirmed the moment they arrive.

As an example, assume website Z accepts incoming Bitcoin payments, but also trusts the green address published by [[Mt. Gox]]. Customer C wants to withdraw funds from Mt. Gox and send them to a payment address of website Z. A customer who does a withdrawal from Mt. Gox can click the ''use green address'' checkbox, which will result in the payment being sent to the green address as an intermediate step before forwarding the payment to site Z. Site Z can confirm that the payment passed through Mt. Gox's green address and trust the payment as confirmed immediately, since it knows that the only party who could potentially perform an attack to reverse the payment is Mt. Gox, which is presumed unlikely.

The concept originated on the forums and was discussed in two threads<ref>https://bitcointalk.org/index.php?topic=48170</ref><ref>https://bitcointalk.org/index.php?topic=32818.0</ref>. Since then, it has been implemented by [[Instawallet]] and [[Mt. Gox]].

==See Also==

* [http://bitcoin.stackexchange.com/questions/1730/what-are-green-addresses/1731#1731 What Are Green Addresses] Q&A on StackExchange

==External Links==
===Sites that allow withdrawals from green addresses===
* [https://mtgox.com MtGox ]
* [[Instawallet]]

===Sites that recognize green addresses===
* [[Btctip|BTCTip]]
* [[BTCPak]]
* [[Instawallet]]

==References==
<references/>

Help:FAQ

2011-06-13T10:20:51Z

Jav: Clarified the part about "number of zeroes"

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”).
A Bitcoin isn't tangible. It is just a number associated with a [[Address|Bitcoin Address]]. See also an [[Introduction|easy intro]] to bitcoin.

=== How can I get Bitcoins? ===

There are five ways to get Bitcoins:

* Buy them on an exchange such as [https://www.mtgox.com/ Mt. Gox] or [http://www.bitcoin-otc.com/ #bitcoin-otc] on FreeNode.
* Accept Bitcoins as payment for goods or services.
* Find a local trader on [http://tradebitcoin.com tradebitcoin] (or somewhere else) and trade with him in cash.
* Create a new [[block]] (currently yields 50 Bitcoins).
* Participate in a [[Pooled mining|mining pool]].

=== Can I buy Bitcoins with Paypal? ===

While it's possible to find an individual who wishes to sell Bitcoin to you via Paypal, (perhaps via [http://www.bitcoin-otc.com/ #bitcoin-otc] ) most major 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 goods. Paypal too often sides with the fraudulent buyer in this case, and so exchangers no longer allow this method of funding.

Buying Bitcoins from individuals with this method is still possible, but requires mutual trust. In this case, Bitcoin seller beware.

=== 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 coins are generated by a network node each time it finds the solution to a certain mathematical problem (i.e. creates a new [[block]]), which is difficult to perform and can demonstrate a [[proof of work]]. The reward for solving a block is [[controlled inflation|automatically adjusted]] so that in the first 4 years of the Bitcoin network, 10,500,000 BTC will be created. The amount is halved each 4 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 coins will approach 21,000,000 BTC over time.

In addition, built into the network is a system that attempts to allocate new coins in blocks about every 10 minutes, on average, somewhere on the network. As the number of people who attempt to generate these new coins changes, the difficulty of creating new coins changes. This happens in a manner that is agreed upon by the network as a whole, based upon the time taken to generate the previous 2016 blocks. The difficulty is therefore related to the average computing resources devoted to generate these new coins over the time it took to create these previous blocks. The likelihood of somebody "discovering" one of these blocks is based on the computer they are using compared to all of the computers also generating blocks on the network.

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

[http://blockexplorer.com/q/totalbc Current count]

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? ===

Technically, a Bitcoin can be divided down to 8 decimals using existing data structures, so 0.00000001 BTC is the smallest amount currently possible. Discussions about and ideas for ways to provide for even smaller quantities of Bitcoins may be created in the future if the need for them ever arises.

=== 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)
* 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 units for thousandths, millionths and billionths. 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? ===

The reward will go from 0.00000001 BTC to 0. Then no more coins will likely be created.

The calculation is done as a right bitwise shift of a 64-bit signed integer, which means it is divided by 2 and rounded down. The integer is equal to the value in BTC * 100,000,000. This is how all Bitcoin balances/values are stored internally.

Keep in mind that using current rules this will take nearly 100 years before it becomes an issue and Bitcoins may change considerably before that happens.

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

The last block that will generate coins will be block #6,929,999. This should be generated around year 2140. Then the total number of coins in circulation will 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 20999999.999999999496 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, what will sustain the ability to use bitcoins will be these fees entirely. There will be blocks generated after block #6,929,999, assuming that people are still using Bitcoins at that time.

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

Not at all. 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 when Bitcoins are lost, the remaining Bitcoins will increase in value to compensate. As the value of Bitcoins increase, the number of Bitcoins required to purchase an item '''de'''creases. This is known as a [[Deflationary spiral|deflationary economic model]]. Eventually, if and when it gets to the point where the largest transaction is less than 1BTC, then it's a simple matter of shifting the decimal place to the right a few places, and the system continues.

=== 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 couple of racks of machines using todays hardware). It's worth noting that the MasterCard network is structured somewhat like BitCoin itself - as a peer to peer broadcast network.

Learn more about [[Scalability]].

=== 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.

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!

Why ten minutes specifically? It is a tradeoff chosen by Satoshi between propagation time of new blocks in large networks and the amount of work wasted due to chain splits. If that made no sense to you, don't worry. Reading [http://www.bitcoin.org/bitcoin.pdf the technical paper] should make things clearer.

=== Do you have to wait 10 minutes in order to buy or sell things with BitCoin? ===

No, it's reasonable to sell things without waiting for a confirmation as long as the transaction is not of high value.

When people ask this question they are usually thinking about applications like supermarkets or snack machines, as discussed in [http://www.bitcoin.org/smf/index.php?topic=423.msg3819#msg3819 this thread from July 2010]. Zero confirmation transactions still show up in the GUI, but you cannot spend them. You can however reason about the risk involved in assuming you ''will'' be able to spend them in future. In general, selling things that are fairly cheap (like snacks, digital downloads etc) for zero confirmations will not pose a problem if you are running a well connected node.

=== 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''.

==Economy==
=== Where does the value of Bitcoin stem from? What backs up Bitcoin? ===
Bitcoins have value because they are accepted as payment by many. 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. In a sense, you could say that Bitcoin is "backed up" by the price tags of merchants – a price tag is a promise to exchange goods for a specified amount of currency.

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.

=== What if someone bought up all the existing Bitcoins? ===
What if somebody bought up all the gold in the world? Well, by attempting to buy it all, the buyer would just drive the prices up until he runs out of money.

Not all Bitcoins are for sale. Just as with gold, no one can buy a Bitcoin that isn't available for sale.

=== Bitcoin's monetary policy causes a deflationary spiral ===
See the article [[Deflationary spiral]].

=== 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.

=== 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 profit from the usefulness of a stable and widely accepted p2p currency.

The fact that early adopters benefit more doesn't alone make anything a ponzi scheme. Apple stocks aren't ponzi even though the early investors got rich.

==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. Bitcoin will also try to connect to IRC (tcp port 6667) to meet other nodes to connect to.

If you want to restrict your firewall rules to a few ips and/or don't want to allow IRC connection, you can find stable nodes in the [[Fallback Nodes|fallback nodes list]]. If your provider blocks the common IRC ports, note that lfnet also listens on port 7777. Connecting to this alternate port currently requires either recompiling Bitcoin, or changing routing rules. For example, on Linux you can evade a port 6667 block by doing something like this:

echo 173.246.103.92 irc.lfnet.org >> /etc/hosts
iptables -t nat -A OUTPUT -p tcp --dest 173.246.103.92 --dport 6667 -j DNAT --to-destination :7777 -m comment --comment "bitcoind irc connection"

=== How does the peer finding mechanism work? ===
Bitcoin finds peers primarily by connecting to an IRC server (channel #bitcoin on irc.lfnet.org). If a connection to the IRC server cannot be established (like when connecting through TOR), an in-built node list will be used and the nodes will be queried for more node addresses.

==Mining==
===What is mining?===
Mining is the process of spending computation power to find valid blocks and thus create new Bitcoins.

Technically speaking, mining is the calculation of a [[hash]] of the previous block and a [[nonce]]. If the hash value is found to be less than the current [[difficulty]], a new block is formed and the miner gets 50 newly generated Bitcoins. If the hash is not less than the current difficulty, a new nonce is used, and a new hash is calculated. This is done thousands or millions of times per second by each miner.

===I've been mining for a long time and haven't created any new Bitcoins. What's wrong?===

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- or time-effective method of mining is using a high-end graphics card with special software (see also [[Why a GPU mines faster than a CPU]]). Since CPU mining is essentially useless, it may be removed from future versions of the Bitcoin software.

===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.

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.

===Is it not a waste of energy?===
Spending energy on creating 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.

==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

==See Also==

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

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

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

Help:FAQ

2011-06-13T10:00:05Z

Jav: Elaborated on what exactly is computed during the mining process

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”).
A Bitcoin isn't tangible. It is just a number associated with a [[Address|Bitcoin Address]]. See also an [[Introduction|easy intro]] to bitcoin.

=== How can I get Bitcoins? ===

There are five ways to get Bitcoins:

* Buy them on an exchange such as [https://www.mtgox.com/ Mt. Gox] or [http://www.bitcoin-otc.com/ #bitcoin-otc] on FreeNode.
* Accept Bitcoins as payment for goods or services.
* Find a local trader on [http://tradebitcoin.com tradebitcoin] (or somewhere else) and trade with him in cash.
* Create a new [[block]] (currently yields 50 Bitcoins).
* Participate in a [[Pooled mining|mining pool]].

=== Can I buy Bitcoins with Paypal? ===

While it's possible to find an individual who wishes to sell Bitcoin to you via Paypal, (perhaps via [http://www.bitcoin-otc.com/ #bitcoin-otc] ) most major 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 goods. Paypal too often sides with the fraudulent buyer in this case, and so exchangers no longer allow this method of funding.

Buying Bitcoins from individuals with this method is still possible, but requires mutual trust. In this case, Bitcoin seller beware.

=== 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 coins are generated by a network node each time it finds the solution to a certain mathematical problem (i.e. creates a new [[block]]), which is difficult to perform and can demonstrate a [[proof of work]]. The reward for solving a block is [[controlled inflation|automatically adjusted]] so that in the first 4 years of the Bitcoin network, 10,500,000 BTC will be created. The amount is halved each 4 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 coins will approach 21,000,000 BTC over time.

In addition, built into the network is a system that attempts to allocate new coins in blocks about every 10 minutes, on average, somewhere on the network. As the number of people who attempt to generate these new coins changes, the difficulty of creating new coins changes. This happens in a manner that is agreed upon by the network as a whole, based upon the time taken to generate the previous 2016 blocks. The difficulty is therefore related to the average computing resources devoted to generate these new coins over the time it took to create these previous blocks. The likelihood of somebody "discovering" one of these blocks is based on the computer they are using compared to all of the computers also generating blocks on the network.

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

[http://blockexplorer.com/q/totalbc Current count]

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? ===

Technically, a Bitcoin can be divided down to 8 decimals using existing data structures, so 0.00000001 BTC is the smallest amount currently possible. Discussions about and ideas for ways to provide for even smaller quantities of Bitcoins may be created in the future if the need for them ever arises.

=== 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)
* 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 units for thousandths, millionths and billionths. 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? ===

The reward will go from 0.00000001 BTC to 0. Then no more coins will likely be created.

The calculation is done as a right bitwise shift of a 64-bit signed integer, which means it is divided by 2 and rounded down. The integer is equal to the value in BTC * 100,000,000. This is how all Bitcoin balances/values are stored internally.

Keep in mind that using current rules this will take nearly 100 years before it becomes an issue and Bitcoins may change considerably before that happens.

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

The last block that will generate coins will be block #6,929,999. This should be generated around year 2140. Then the total number of coins in circulation will 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 20999999.999999999496 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, what will sustain the ability to use bitcoins will be these fees entirely. There will be blocks generated after block #6,929,999, assuming that people are still using Bitcoins at that time.

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

Not at all. 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 when Bitcoins are lost, the remaining Bitcoins will increase in value to compensate. As the value of Bitcoins increase, the number of Bitcoins required to purchase an item '''de'''creases. This is known as a [[Deflationary spiral|deflationary economic model]]. Eventually, if and when it gets to the point where the largest transaction is less than 1BTC, then it's a simple matter of shifting the decimal place to the right a few places, and the system continues.

=== 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 couple of racks of machines using todays hardware). It's worth noting that the MasterCard network is structured somewhat like BitCoin itself - as a peer to peer broadcast network.

Learn more about [[Scalability]].

=== 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.

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!

Why ten minutes specifically? It is a tradeoff chosen by Satoshi between propagation time of new blocks in large networks and the amount of work wasted due to chain splits. If that made no sense to you, don't worry. Reading [http://www.bitcoin.org/bitcoin.pdf the technical paper] should make things clearer.

=== Do you have to wait 10 minutes in order to buy or sell things with BitCoin? ===

No, it's reasonable to sell things without waiting for a confirmation as long as the transaction is not of high value.

When people ask this question they are usually thinking about applications like supermarkets or snack machines, as discussed in [http://www.bitcoin.org/smf/index.php?topic=423.msg3819#msg3819 this thread from July 2010]. Zero confirmation transactions still show up in the GUI, but you cannot spend them. You can however reason about the risk involved in assuming you ''will'' be able to spend them in future. In general, selling things that are fairly cheap (like snacks, digital downloads etc) for zero confirmations will not pose a problem if you are running a well connected node.

=== 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''.

==Economy==
=== Where does the value of Bitcoin stem from? What backs up Bitcoin? ===
Bitcoins have value because they are accepted as payment by many. 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. In a sense, you could say that Bitcoin is "backed up" by the price tags of merchants – a price tag is a promise to exchange goods for a specified amount of currency.

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.

=== What if someone bought up all the existing Bitcoins? ===
What if somebody bought up all the gold in the world? Well, by attempting to buy it all, the buyer would just drive the prices up until he runs out of money.

Not all Bitcoins are for sale. Just as with gold, no one can buy a Bitcoin that isn't available for sale.

=== Bitcoin's monetary policy causes a deflationary spiral ===
See the article [[Deflationary spiral]].

=== 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.

=== 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 profit from the usefulness of a stable and widely accepted p2p currency.

The fact that early adopters benefit more doesn't alone make anything a ponzi scheme. Apple stocks aren't ponzi even though the early investors got rich.

==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. Bitcoin will also try to connect to IRC (tcp port 6667) to meet other nodes to connect to.

If you want to restrict your firewall rules to a few ips and/or don't want to allow IRC connection, you can find stable nodes in the [[Fallback Nodes|fallback nodes list]]. If your provider blocks the common IRC ports, note that lfnet also listens on port 7777. Connecting to this alternate port currently requires either recompiling Bitcoin, or changing routing rules. For example, on Linux you can evade a port 6667 block by doing something like this:

echo 173.246.103.92 irc.lfnet.org >> /etc/hosts
iptables -t nat -A OUTPUT -p tcp --dest 173.246.103.92 --dport 6667 -j DNAT --to-destination :7777 -m comment --comment "bitcoind irc connection"

=== How does the peer finding mechanism work? ===
Bitcoin finds peers primarily by connecting to an IRC server (channel #bitcoin on irc.lfnet.org). If a connection to the IRC server cannot be established (like when connecting through TOR), an in-built node list will be used and the nodes will be queried for more node addresses.

==Mining==
===What is mining?===
Mining is the process of spending computation power to find valid blocks and thus create new Bitcoins.

Technically speaking, mining is the calculation of a [[hash]] of the previous block and a [[nonce]]. If the hash value is found to be less than the current [[difficulty]], a new block is formed and the miner gets 50 newly generated Bitcoins. If the hash is not less than the current difficulty, a new nonce is used, and a new hash is calculated. This is done thousands or millions of times per second by each miner.

===I've been mining for a long time and haven't created any new Bitcoins. What's wrong?===

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- or time-effective method of mining is using a high-end graphics card with special software (see also [[Why a GPU mines faster than a CPU]]). Since CPU mining is essentially useless, it may be removed from future versions of the Bitcoin software.

===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.

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 starts with a certain number of zeros.

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.

===Is it not a waste of energy?===
Spending energy on creating 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.

==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

==See Also==

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

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

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

Help:Introduction

2011-02-23T17:26:35Z

Jav: Mentioned some monitoring sites at the end of the introduction

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Alice is far away from Bob and wants to buy his [http://www.grasshillalpacas.com/alpacaproductsforbitcoinoffer.html Alpaca socks]. In return, she wants to send him a dollar. A dollar bill is a piece of paper with very low intrinsic value, but which is accepted by people in exchange for valuable products and services in the real world, such as the socks Alice wants to buy. One simple thing Alice can do is to put a dollar bill in an envelope, mail it to Bob, and then wait for Bob to send the socks to her.

Another thing Alice can do is to "wire" the money to Bob. She can do that by first giving her dollar bills to an institution called a bank, the job of which is to safe-keep Alice's dollar bills and, in return, to give Alice a written promise (called a "bank statement") that, whenever she wishes, she can come to the bank to take back the same amount of dollar 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 "giving" the dollar bills to Bob instead of her. This could be done by sending a person to Bob's door, with Alice's dollar bills in hand (or, better, fresh new dollar bills, if Alice's dollar bills are in bad condition), but usually it 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 in his next statement, or, if he is in a hurry, the next time he contacts his bank asking about how much money they have for him.

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 "talking" to the customers instead of paid bank employees. The job of these machines is to learn what each customer wants to do with his/her money and, to the extent that it's possible, act on what the customer wants (for example, ATMs can hand cash). In the end, there is very little human involvement in this process, most of the time. The people can always know how much money out of the money that the bank is safe-keeping is theirs, and they are confident that the numbers they see in their bank statements and on their computer screens stand for the number of dollar bills that that they can get from the bank at any time they wish. They can be so sure of that, that they can accept those numbers in the same way they accept paper dollars (this is similar to the way people started accepting paper dollars as they accepted gold or silver).

However, the fact that machines are used does not change the structure of this system, which is, as it was, based on a central authority (the bank) which is responsible for keeping records about how much money belongs to whom. Everybody has to rely on this central authority to be honest (i.e. to say the truth about how much money they are safe-keeping in total, or at least to make the paper money available upon demand from the owners). Also, every person has to identify him/herself to this authority, by giving his/her real name, in order to be allowed to get their paper bills back or to send money to another person.

Bitcoin is a system of owning and voluntarily transferring amounts of so-called bitcoins, in a manner similar to an on-line banking interface, but anonymously and without reliance on a central authority to decide on what is true. These bitcoins are valuable because they require the spending of real resources (CPU time and electricity) to produce, and they cannot be counterfeited or removed from a person's ownership without illicit access to his/her computer.

==Preventing stealing==
To guarantee that an eavesdropper, Eve, cannot access other people's bitcoins by creating transactions in their names we use a [[Wikipedia:Public-key_cryptography|public key system]] to make digital signatures. In this system, each person, such as Alice and Bob, has a pair of public and private keys which he/she stores in a safe [[Wallet|wallet]]. Only the user with his secret private key can sign a document, such as the transaction to give some of his bitcoins to somebody else, but any one can validate the signature using the user’s public key. The bitcoins, in Alice's hands, already contain a signature by whoever sent her the amount.

* Bob sends his public key to Alice.
* Alice adds Bob’s public key along with the amount she wants to transfer, to the transaction.
* Alice signs the transaction with her secret private key.

As a result, anyone who knows the public keys of both Alice and Bob can now see that Alice agreed to transfer the amount to Bob.

Later on, when Bob will transfer the same coins to Charley, he will do the same thing: receive from Charley his public key, add a new transaction to the chain of transactions and sign it with his (Bob) private key. But only Bob can do this, because only Bob has the private key which is necessary for signing and which is the only private key to match Bob’s public key that is already in the chain.

Eve cannot change who the coins belong to by replacing Bob’s public key with her public key, because Alice signed the transfer to Bob using her private key, declaring that the coins now belong to Bob, and Alice's private key is kept secret from Eve. So if Charley 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 counterfeiting==
This is how we guarantee that Alice cannot replicate the coin and use it in more than one transaction:

* Details about the [[Transactions|transaction]] are [[Network|sent]] to as many other people's computers as possible
* At least one of the computers sends back a [[Blocks|block]], which is just a large document that includes details of many transactions. The block is sent to as many other people as possible.
* Eventually the block reaches Bob who can validate that his transaction was recorded and no other transaction for the same coin was made in the past.

In theory, Alice could generate a spoofed block in which her past usage of the same coin does not appear and try to send this block to Bob as evidence that the coin is still hers. However, that past transaction, which contains a signature from Alice, has already been announced and has already been distributed to a very large number of computers in the bitcoin network. Since the process of generating a block is designed to take a [[Proof_of_work|long time]] and all transactions must be given in such blocks, Alice will be unable to compete with all these computers in the rate with which she can generate blocks. Bob will receive much more blocks from third persons than Alice alone will ever be able to generate, and some of these blocks will contain Alice's previous transaction, telling Bob that Alice has already spent her coin. And since, in the presence of multiple parallel chains of blocks of transactions, the longest such chain is taken as the truth, the only way for Alice to "pass" her own version of events is to be in a position to command the majority of the CPU power on the network. We assume nobody can do that, therefore Alice cannot undo what she did and cannot spend her coin twice.

==Privacy==
In order to protect his [[Anonymity|privacy]], Bob can generate a new public-private key pair for each transaction. So David receiving the coin from Charley will not be able to identify who is the second person in the list of transactions. The only thing David will know is the [[Address|address]] of Bob which is a shortened (hashed) version of his public key.

==Creation of coins==
As we saw, both Bob and Charley need to verify that the original coin from Alice is valid. Alice cannot simply generate coins instantly, out of thin air, because the appearance of a coin is a transaction that needs to be accepted by others (it must appear at some place in the chain of blocks). The way that new coins are slowly introduced is this: every computer that manages to generate a block is allowed to put one transaction there in which it gains 50 BTC, without this amount having to come from somewhere. Other computers receiving the block can easily see that the block is valid and accept that this amount belongs to the computer that generated the block. This is called a "proof of work", because generating blocks is a [[Target|slow]] process that requires Alice to spend real resources (buy recent computer hardware, use electricity and CPU time) and in this way it can be compared to gold mining. Only with a proof of work is Alice allowed to contribute to the [[Block_chain|chain of blocks]] that together keep a record of all transactions. The coin received by Alice is an incentive for her to perform this computation work. In addition to this, Alice can shave a small, voluntary [[Transaction_fee|fee]] from the transactions stored in the block.

==Putting it all together==
Directly experience the system in action by visting [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, should be around 6. Also notice the number of transactions and the total amount transfered 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, drill into one of these blocks.
Start by noticing that the block's [[hash|hash]] begins with a run of zeros, this is what made making it so difficult.
The computer that generated this block had to run on many ''Nonce'' values (also listed on the block's page) until it found one that generated this run of zeros.
Next notice 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 notice all the transactions the block contains. The first transaction is the income earned by the computer that generated this block. It includes a fixed amont of coins created out of thin air and possibly fee collected from other transactions in the same block. Several blocks starting from the same block could have been generated in parallel but at the end all the computers in the network agree that only one of these blocks is accepted to be part of the block chain. Other blocks are rejected either because they didn't play according to the rules of the game or they missed out on some of the transactions.

Drill into any of the transactions and you will see how it is made from one or more amounts coming in and out.
The fact that there can be more than one incoming and outgoing amounts, allow the system to join and break amounts in any possible way allowing for any fractional amount needed (usually cents.)
Each incoming amount is a transaction from the past (which you can also drill to) coming from an address of someone
and each outgoing amount is addressed to someone and will be part of a future transaction (which you can also drill too if it also had already taken place.)

Finally you can drill into any of the [[Address|addresses]] and see what public information is available.

To get an impression of the amount of activity on the Bitcoin network, you might like to visit the monitoring websites [http://www.bitcoinwatch.com Bitcoin Watch] and [http://www.bitcoinmonitor.com Bitcoin Monitor]. The first has general statistics on the amount and size of transactions, while the latter shows a real-time visualization of events on the Bitcoin network.

==See Also==

* Installing Bitcoin [[getting started]]
* [[How bitcoin works]]
* [[Using Bitcoin]]
* A gentle introduction to Bitcoin - [[BitcoinMe]]
* Another introduction, ''The Rebooting Of Money'' podcast is found at [[Bitcoin Money]]

Bitcoin Wiki:Community portal

2011-02-09T21:13:07Z

Jav: Started a section on monitoring websites

== Bitcoin Community Forums ==

* [http://www.bitcoin.org/smf/ Official Bitcoin.org Forum]
* [http://www.bitcoinme.com/discussion-forum.html BitcoinMe Forum]
* [http://groups.google.com/group/bitcoin-discussion Bitcoin google group]
* [https://bitcoin.in/forum/ Bitcoin.in forum (SMF)]

== IRC Chat ==

* [irc://irc.freenode.net/bitcoin-discussion General Bitcoin-related] ([http://webchat.freenode.net/?channels=bitcoin-discussion&uio=d4 webchat])
* [irc://irc.freenode.net/bitcoin-dev Development and technical discussion] ([http://webchat.freenode.net/?channels=bitcoin-dev&uio=d4 webchat]) ([http://veritas.maximilianeum.ch/bitcoin/irc/logs archive])
* [irc://irc.freenode.net/bitcoin-otc Over The Counter exchange] ([http://webchat.freenode.net/?channels=bitcoin-otc&uio=d4 webchat])
* [irc://irc.freenode.net/bitcoin-market Live streaming quotes from MtGox and BCM] ([http://webchat.freenode.net/?channels=bitcoin-market&uio=d4 webchat])
* [irc://irc.freenode.net/bitcoin-auction Live auctions] ([http://webchat.freenode.net/?channels=bitcoin-otc&uio=d4 webchat])
* [irc://irc.freenode.net/bitcoin-mining GPU mining related] ([http://webchat.freenode.net/?channels=bitcoin-mining&uio=d4 webchat])
* [irc://irc.freenode.net/bc-news RSS News related to Bitcoin] ([http://webchat.freenode.net/?channels=bc-news&uio=d4 webchat])

There also are IRC channels for for-profit initiatives such as [[Bitcoind Investment Club]] and [[Witcoin]].

==Wiki Users==

* [http://en.bitcoin.it/wiki/Special:ListUsers List of Users] registered on the Bitcoin wiki.

== Events ==

* [[Bitcoin:Tokyo Meetup|Tokyo Meetup]]
* [http://www.meetup.com/bitcoin New York Bitcoin Users Meetup Group]
* [http://www.meetup.com/BitcoinDC Washington, DC Bitcoin Users Group]

==Bitcoin Related Publications==

* [[The Bitcoin Times]] weekly newspaper
* [[The Bitcoin Fiat Times]] satire newspaper
* See [[:Category:Blogs|Blogs]] category

== Maps ==
* The [[Bitcoin Map (Collaborative map)|Bitcoin Map]] collaborative map

== Monitoring ==
* [http://bitcoincharts.com/markets/ Bitcoin Charts] displays an overview of Bitcoin exchange markets.
* The [http://www.bitcoinmonitor.com/ Bitcoin Monitor] visualizes transactions, new blocks and trades on markets as they are happening.
* [http://www.bitcoinwatch.com/ Bitcoin Watch] has various statistics on things like the size of the economy or the number of transactions.

== Bitcoin Project ==
* [http://www.bitcoin.org Bitcoin.org] Official project site
* [http://fivegrinder.com FiveGrinder.com] Project planning and Activism
* [[:Category:Developer|Developer]] pages