Bitcoin Wiki - User contributions [en]

Securing your wallet

2011-06-22T08:30:23Z

Brendan: /* Linux */

==Introduction==

Wallet security can be broken down into two independent goals:
# Protecting your wallet against loss.
# Protecting your wallet against theft.

In the case that your current wallet hasn't been protected adequately (e.g. put online with a weaker password):
# Making a new secure wallet, using appropriate long-term protection.

==Technical Background==

Bitcoin transactions send Bitcoins to a specific public key. A Bitcoin address is an encoded hash of a public key. In order to use received Bitcoins, you need to have the private key matching the public key you received with. This is sort of like a super long password associated with an account (public key). Your Bitcoin wallet contains all of the private keys necessary for spending your received transactions. If you delete your wallet without a backup, then you no longer have the authorization information necessary to claim your coins, and the coins associated with those keys are lost forever.

The wallet contains a pool of queued keys. By default there are 100 keys in the [[key pool]]. The size of the pool is configurable using the "-keypool" command line argument. When you need an address for whatever reason (send, “new address”, generation, etc.), the key is not actually generated freshly, but taken from this pool. A brand new address is generated to fill the pool back to 100. So when a backup is first created, it has all of your old keys plus 100 unused keys. After sending a transaction, it has 99 unused keys. After a total of 100 new-key actions, you will start using keys that are not in your backup. Since the backup does not have the private keys necessary for authorizing spends of these coins, restoring from the old backup will cause you to lose Bitcoins.

Creating a new address generates a new pair of public and private keys, which are added to your wallet. Each keypair is mostly random numbers, so they cannot be known prior to generation. If you backup your wallet and then create more than 100 new addresses, the keypair associated with the newest addresses will not be in the old wallet because the new keypairs are only known after creating them. Any coins received at these addresses will be lost if you restore from the backup.

The situation is made somewhat more confusing because the receiving addresses shown in the UI are not the only keys in your wallet. Each Bitcoin generation is given a new public key, and, more importantly, each sent transaction also sends some number of Bitcoins back to yourself at a new key. When sending Bitcoins to anyone, you generate a new keypair for yourself and simultaneously send Bitcoins to your new public key and the actual recipient's public key. This is an anonymity feature – it makes tracking Bitcoin transactions much more difficult.

So if you create a backup, do more than 100 things that cause a new key to be used, and then restore from the backup, some Bitcoins will be lost. Bitcoin has not deleted any keys (keys are never deleted) – it has created a new key that is not in your old backup and then sent Bitcoins to it.

== Making a new wallet ==

In the case that a wallet has been distributed, or stored, in a (real or potential) compromised state, it is wise to create a new wallet and transfer the full balance of Bitcoins to an address contained only in the newly created wallet.

For example, this will be necessary if one created a wallet with a password of 12 characters, as suggested. However a few years have passed and the wallet is now more easily compromised. Just re-encrypting isn't secure. One needs to make a new wallet and make the old wallet worthless (spending the funds to the new wallet).

==Making a secure workspace==

===Linux===

The first step is to make a [http://www.howtogeek.com/howto/ubuntu/add-a-user-on-ubuntu-server/ new user,] so run:

<code>adduser new_user_name</code>

as root. When you get to the prompt 'Enter the new value, or press ENTER for the default', just keep hitting ENTER.

Then switch user to the new user. To get to the new user you can use the switch user icon for your system, which on Ubuntu is in the 'System/Quit' screen, or if there is no switch icon on your system you can log out and log back in as the new user. Then click on a folder in the new user to display the file browser, then keep going up folders until you see the new user home directory, then right click to bring up the Properties dialog, then click on the Permissions tab, then in the Others section, set the folder access to None.

For secure browsing, open Firefox, and then go into the Edit menu and click Preferences. Starting from the left, click on the General tab, and in the 'Startup/When Firefox starts' pop up menu, choose 'Show a Blank Page'. Then click on the Content tab, and deselect 'Load images automatically' and deselect 'Enable Javascript'. Then click on the Privacy tab, and in the 'History/Firefox will' pop up menu, choose 'Never remember history'. Then click on the Security tab, and in the Passwords section, deselect 'Remember passwords for sites' and deselect 'Use a master password'. Then click on the Advanced tab, then click on the Update tab, and then in the 'Automatically check for updates to' section, deselect 'Add-ons' and 'Search Engines'.

When javascript is disabled, the [http://sourceforge.net/projects/bitcoin/files/Bitcoin/bitcoin-0.3.23/bitcoin-0.3.23-linux.tar.gz/download linux download page] will not download automatically, so you'll have to click on the 'direct link' part of the "Problems with the download? Please use this 'direct link' or try another mirror." line.

After you've made your secure new user, to maintain security you should use it only for bitcoin.

===Mac===

=====Backup all data (500MB)=====
Follow these instructions to backup all the bitcoin data (wallet and block chains) to an encrypted disk image.
# Open Disk Utility
# Click New Image and choose 500MB, 128-bit or 256-bit (faster or more secure) encryption and single partition.
# Save it somewhere you won't lose it (like your Dropbox, Strongspace or whatever)
# Choose a safe and strong password
# Move everything from ~/Library/Application Support/Bitcoin/ to the image
# Symlink it back so the app would be able to use it
:::ln -s /Volumes/Bitcoin ~/Library/Application Support/Bitcoin

Don't forget to mount your image before using Bitcoin and unmount after quitting it.

=====Backup just wallet.dat (40MB)=====
Follow these instructions to backup just the wallet.dat file. This results in a smaller disk image, but it's more complicated to do.
# Open Disk Utility
# Click New Image and choose 40MB, 128-bit or 256-bit (faster or more secure) encryption and single partition.
# Save it somewhere you won't lose it (like your Dropbox, Strongspace or whatever)
# Choose a safe and strong password
# Move your wallet.dat file to the image
# Symlink it back so the app would be able to use it
:::ln -s /Volumes/Bitcoin/wallet.dat ~/Library/Application Support/Bitcoin/wallet.dat

[[File:MountWalletAndLauchnBitcoin_OSX_Automator.png|thumbnail|150px|Mount Wallet and launch Bitcoin]]
Don't forget to mount your image before using Bitcoin and unmount after quitting it.

'''Note''': If you start the Bitcoin application without having the image mounted, the application will overwrite your symlink with a new wallet. If that happens, don't panic. Just delete the new wallet.dat, mount the image, and recreate the symlink like above.

'''Automation''': You can create a small application using [http://en.wikipedia.org/wiki/Automator_%28software%29 Automator] (included in OS X) to automatically mount the wallet and then launch Bitcoin App. See the Screenshot on how to do this.

===Windows===

If you are using Windows XP or Windows 7, you can keep your wallet on an encrypted disk image created by third-party software, such as [http://www.truecrypt.org/ TrueCrypt] (open source) or [http://www.jetico.com/encryption-bestcrypt/ Jetico BestCrypt] (commercial). You can probably do the same with Windows Vista (but why would you use that?) or Windows 2000.

'''NOTE:''' You should configure BitCoin in this manner only on computers where you use BitCoin, but do not use that computer to mine. For example, this is a good configuration for a notebook or tablet computer.

Assuming that you have installed the Windows BitCoin client and run it at least once, the process is described below.

To mount the BitCoin data directory on an encrypted drive
<ol start=1 type=1>
<li>Use the third-party disk image encryption program of your choice to create and mount an encrypted disk image of at least 100 MB in size.</li>
<li>Locate the BitCoin data directory, and copy the directory with all contents to the encrypted drive.
For help finding this directory, see [[Securing_your_wallet#Locating_BitCoin_s_data_directory|Locating BitCoin's Data Directory]].</li>
<li>Create a Windows shortcut that starts BitCoin with the <code>-datadir</code> parameter and specifies the encrypted drive and directory.
For example, if you installed Bitcoin in the default directory, mounted your BitCoin encrypted drive as <code>E:\</code>, and stored your BitCoin data directory on it as <code>Bitcoin</code>, you would type the following command as the shortcut Target:
<blockquote><code>C:\Program Files\Bitcoin\bitcoin.exe -datadir=E:\Bitcoin</code></blockquote></li>
<li>Open BitCoin's settings and configure it NOT to start automatically when you start Windows.
This is to allow you to mount the BitCoin encrypted disk image before starting BitCoin.</li>
<li>Shut down BitCoin, and then restart it from the new shortcut.</li>
</ol>

After doing this, any time you want to use BitCoin, you must first mount the BitCoin encrypted disk image using the same drive designation, and then run BitCoin from the shortcut that you created, so that it can find its data and your wallet. :-)

== Locating BitCoin's data directory ==

The [[data directory]] is the location where Bitcoin's data files are stored, including the wallet data file.

=== Windows ===

Go to Start -> Run (or press WinKey+R) and run this:

explorer %APPDATA%\BitCoin

BitCoin's data folder will open. For most users, this is the following locations:

C:\Documents and Settings\YourUserName\Application data\BitCoin (XP)

C:\Users\YourUserName\Appdata\Roaming\BitCoin (Vista and 7)

"AppData" and "Application data" are hidden by default.

=== Linux ===

By default BitCoin will put its data here:

~/.bitcoin/

You need to do a "ls -a" to see directories that start with a dot.

If that's not it, you can do a search like this:

find / -name wallet.dat -print 2>/dev/null

=== Mac ===

By default BitCoin will put its data here:

~/Library/Application Support/Bitcoin/

==Backup==

The only file you need to back up is "wallet.dat". Ensure that BitCoin is closed, copy this file somewhere else, encrypt it, and put it somewhere safe. Ideally, you would put this file in two places: one nearby, and one 100+ miles away.

You can use the [[api|backupwallet]] JSON-RPC command to back up without shutting down Bitcoin.

=== General Solutions ===

Your wallet.dat file is not encrypted by BitCoin. Anyone who can access it can easily steal all of your coins. Use one of these encryption programs if there is any chance someone might stumble upon your wallet.
* [http://www.7-zip.org/ 7-zip] - Supports strongly-encrypted archives.
* [http://www.axantum.com/axcrypt/ AxCrypt]
* [http://lrzip.kolivas.org lrzip] - Compression software for Linux and OSX that supports very high grade password protected encryption
* [http://www.truecrypt.org/ TrueCrypt] - Volume-based on-the-fly encryption (for advanced users)
* [http://www.rarlab.com/ WinRar] - Commonly used archive software that supports verification records and encryption.

There is also a list of [[OpenSourceEncryptionSoftware|open source encryption software.]]

==== Password Strength ====
Brute-force password cracking has come a long distance, a previously thought secure password of random [a-Z] [0-9] [!-~] of 8 characters long can be trivially solved now (using appropriate hardware)... The recommended length is '''at least''' 12 characters long. You can also use a multi-word password. [http://www.baekdal.com/tips/password-security-usability The Usability of Passwords]

If you use keyfiles in addition to a password, it is unlikely that your encrypted file can ever be cracked using brute force methods, even 10 years from now when even a 12 character password might be too short.

Assume that any encrypted files you store online (eg. gmail, Dropbox) will be stored somewhere forever and can never be erased.

==== Storage of Archive ====
One of the most simple methods for storing a appropriately '''encrypted''' archive of your wallet.dat file is to send the archive as an email attachment to your own e-mail address. Services like gmail.com use very comprehensive distributed networks that make the loss of data very unlikely. One can even obfuscate the name of the files within the archive, and name the archive something less inviting, such as: 'personal notes' or 'car insurance'.

Another solution is to use a file storage service like [http://www.wuala.com/bitcoin Wuala] ( encrypted, [http://www.bitcoin.org/smf/index.php?topic=5817.0 instructions]), [http://www.dropbox.com Dropbox] and [http://en.wikipedia.org/wiki/Comparison_of_online_backup_services others], including the more secure [http://www.spideroak.com SpiderOak].

=== Linux solution ===

Linux users can setup cron by running 'crontab -e' and adding this line:

01 */1 * * * /usr/local/bin/backupwallet.sh

This cron line runs backupwallet.sh at the 01 minute of every hour. Remember to add a newline after the last line of the crontab file, or else the last line won't run.

backupwallet.sh:

#!/bin/bash

TS=$(date "+%Y%m%d-%H-%M")
WALLET=/tmp/wallet${TS}
WALLET_E=/tmp/wallet${TS}.crypt

if
echo -n making backup...
bitcoind backupwallet $WALLET
<nowiki>[[ ! -s "$WALLET" ]]</nowiki>
then echo failed
elif
echo done
echo -n encrypting....
! gpg -r myusername --output $WALLET_E --encrypt $WALLET
then echo failed
elif
echo done
echo -n copying to distant server...
! scp $WALLET_E user@myserver.org:~/wallets/
then echo failed
else echo done
fi

rm -f $WALLET $WALLET_E

The shell script:

* Calls bitcoind backupwallet to create a time/date-stamped wallet.
* GPG encrypts the wallet with your public key.
* Copies the result to a backup location.

[[Category:Technical]]

==Restore==

Assuming your backup is recent enough that you haven't used up all of your key pool... restoring a wallet to a new (or old) location and rescanning the block chain should leave you with all your coins. Just follow these steps:
* Quit bitcoin(d).
* Copy your backed up wallet.dat into your bitcoin profile directory.
* If copying into existing profile, delete file ''blkindex.dat'' and ''blk0001.dat'' to make the client re-scan the block chain.
And you'll be good as new.

==Erasing Plain Text Wallets==

A good practice is to keep at least two wallets, one as a "current account" for everyday transactions and one as a "savings account" where you store the majority of your Bitcoins.

The "savings account" wallet should be backed up in encrypted form only and all plaintext copies of this wallet should be erased. In case someone gains unauthorised access to your computer (either by physically stealing it or by exploiting a system vulnerability via the internet), they will only be able to spend the coins in your "current account" wallet.

In most operating systems, including Windows, Linux, and Mac OS X, simply deleting a wallet.dat file will ''not'' generally destroy it. It is likely that advanced tools can still be used to recover the wallet.dat file, even after it has been deleted.

The Linux '''shred''' command can be used to overwrite the wallet file with random data prior to deleting; this particular copy of the file will then be practically impossible to recover. Using shred (and similar tools on Windows) however does not guarantee that still other copies don't exist somewhere hidden on your HD. That will depend on your system configuration and what packages you have installed. Some system restore and backup tools, for instance, create periodic snapshots of your filesystem, duplicating your wallet.dat.

In Mac OS, clicking "Secure Empty Trash" in the Finder menu will shred the contents of the trash can. As with any OS this doesn't guarantee that there are not other copies elsewhere on your system.

For Windows, the built-in command ''cipher /W'' will shred all previously-deleted files. [http://www.cylog.org/utilities/cybershredder.jsp CyberShredder] can securely deleted individual files.

==eWallet==

Storing bitcoins with an [[eWallet]] provider incurs risks as well. Basically you grant the third party, in this case eWallet, full access to your wallet.

==See Also==

* [[Data directory]]

[[de:Sichere deine Geldbörse]]
[[zh-cn:保护你的钱包]]

Help:Installing Bitcoin Core

2011-06-22T07:57:41Z

Brendan: Typo: 'minted' -> 'mined'. Removed double spaces

An account can effortlessly be created using an [[eWallet]] service. eWallet services provide an online wallet to hold your bitcoins.

This guide covers installing Bitcoin without needing a third party wallet service.

== For Windows computers ==

=== Installation ===
[http://sourceforge.net/projects/bitcoin/ Download] and install Bitcoin.

[[File:Install fin.png|frame|none|Complete installation wizard]]

=== Initialization ===

The first time you run Bitcoin, it needs to download all the blocks to setup. You already have your bitcoin address at this point, but you won't see any transactions before the initialisation is complete (it can take from half to a few hours).

[[File:First time run fin.png|frame|none|Bitcoin is initialising by establishing a connection to other clients and downloading the blocks.]]

[[File:Bitcoin all blocks fin.png|frame|none|Completed download of block-chain.]]

Your address (you can have as many as you want) is at the top. Below is your balance which will be zero. The list below shows your transactions.

== For Mac computers ==

Download the [http://sourceforge.net/projects/bitcoin/files/Bitcoin/bitcoin-0.3.19/bitcoin-0.3.19-macosx.zip/download OS X version] of Bitcoin and expand the archive.

[[File:BcOSX.png|thumb|none|Contents of the Bitcoin archive after expansion]]

Drag the Bitcoin icon to the desired install location, and double-click or Cmd-O (⌘O) to run the application. The Bitcoin window will open and connections will start up in minutes. The blocks will begin downloading. Your address and balance are at the top of the window. Click "Copy to Clipboard" to copy your address. Transactions are displayed in the main window.

[[File:BcOSXrunning.png|thumb|none|Main window]]

As Bitcoin currently does not support hiding with Cmd-H (⌘H), it is recommended that users tick the "Minimize on close" option in the Preferences menu to prevent accidental program exits.

[[File:BcOSXPreferences.png|thumb|none|Preferences window on OS X]]

== Getting my first coins ==

The [[Bitcoin Faucet]] [https://freebitcoins.appspot.com/ website] currently hands out 0.02 BTC to new bitcoin users. Fill in the form with your bitcoin address. When you wish to add more, view [[Buying bitcoins]].

[[File:Get some btc.png|frame|none|Getting free coins from the Faucet]]

A new entry should appear in Bitcoin. The network hasn't yet confirmed it, but you know it's being processed. After about one hour it should get 6 confirmations. You are able to spend the coins when there is only one confirmation.

The confirmation counter (like the block counter) will increase by one roughly every 10 minutes. Six confirmations are considered as 100% sure a transfer has been processed.

[[File:First btc recv.png|frame|none]]

[[File:Six confirms bitcoin client.png|frame|none]]

* Play games and enter your first raffle at http://bitgames.jhfire.net!
* Create an account on witcoin and post something (cost 0.01 BTC): http://www.witcoin.com (click "get wit it" to create an account) If your post is any good, you can earn when it gets replies and votes.
* Give a tip to a deserving artist, writer, etc. on YouTipIt.org. For instance, this video creation is worth 0.05 BTC, no?: http://www.youtipit.org/t/2652
* Give lady luck a shot? Double Trouble (49% chance of doubling your money) http://doubletrouble.bitcoinbet.com
* Give to any of the charities on Bitcoin Trade page: http://en.bitcoin.it/wiki/Trade#Donation-accepting_organizations_and_projects

== Points to remember ==

* You don't need to be online to receive BTC.
* You can create as many new addresses as you like. Using a different address each time helps keep you [[Anonymity|anonymous]].
* You can be [[Anonymity|anonymous]] with adequate precautions.
* You cannot send BTC to an invalid address. Typos are not a worry as the payment will refuse to send.
* The [[Wallet|wallet]] file holds the keys that allow spending and thus the computer should be [[Securing_your_wallet|protected]] from the risk of loss and theft.
* Leaving Bitcoin open improves connectivity for the network and ensures that you don't fall behind on the block chain. Also see [[FAQ#Do_I_need_to_configure_my_firewall_to_run_bitcoin?|the FAQ about port forwarding]]

Proceed to the [[Introduction|introduction]]

== Technical ==
=== Block chain ===
The [[block chain]] is a neverending story of every transaction throughout the network from day 1 (genesis). The first time you run Bitcoin, it is downloaded and verified on your computer. Every new transaction is added to the end of this chain and verified by the network to be valid.

=== Addresses ===
Whenever you send a coin, you are actually sending a cryptographically signed message, associating your coin with the recipient's address. This effectively transfers ownership to to the recipient. Once they own the coin, they are free to transfer it to another person.

A wallet is a collection of addresses. You can create as many new addresses as you wish; having more addresses makes you more anonymous, because then people cannot see how much BTC you received. Your wallet contains the secret keys used for spending that money, and must be [[Securing your wallet|backed-up regularly]]. If you lose the wallet then you no longer possess the money.

=== Generating ===
New coins are mined through generating hashes. These generators are rewarded with a small fee for the computationally intensive task of incorporating your transactions into the block-chain. This fee halves each time 210000 blocks are added to the block chain, or approximately every 4 years. The fee will keep halving until it effectively reaches zero, at which point 21 million coins will be in circulation.

[[Category:Introduction]]

[[de:Erste Schritte]]
[[zh-cn:入门]]