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Bitcoin 0.4.1 BETA
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Copyright (c) 2009-2011 Bitcoin Developers
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Distributed under the MIT/X11 software license, see the accompanying
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file license.txt or http://www.opensource.org/licenses/mit-license.php.
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This product includes software developed by the OpenSSL Project for use in
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the OpenSSL Toolkit (http://www.openssl.org/). This product includes
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cryptographic software written by Eric Young (eay@cryptsoft.com).
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Intro
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-----
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Bitcoin is a free open source peer-to-peer electronic cash system that is
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completely decentralized, without the need for a central server or trusted
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parties. Users hold the crypto keys to their own money and transact directly
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with each other, with the help of a P2P network to check for double-spending.
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Setup
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-----
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Unpack the files into a directory and run:
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bin/32/bitcoin (GUI, 32-bit)
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bin/32/bitcoind (headless, 32-bit)
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bin/64/bitcoin (GUI, 64-bit)
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bin/64/bitcoind (headless, 64-bit)
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Wallet Encryption
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-----------------
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Bitcoin supports native wallet encryption so that people who steal your
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wallet file don't automatically get access to all of your Bitcoins.
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In order to enable this feature, chose "Encrypt Wallet" from the
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Options menu. You will be prompted to enter a passphrase, which
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will be used as the key to encrypt your wallet and will be needed
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every time you wish to send Bitcoins. If you lose this passphrase,
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you will lose access to spend all of the bitcoins in your wallet,
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no one, not even the Bitcoin developers can recover your Bitcoins.
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This means you are responsible for your own security, store your
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passphrase in a secure location and do not forget it.
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Remember that the encryption built into bitcoin only encrypts the
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actual keys which are required to send your bitcoins, not the full
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wallet. This means that someone who steals your wallet file will
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be able to see all the addresses which belong to you, as well as the
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relevant transactions, you are only protected from someone spending
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your coins.
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It is recommended that you backup your wallet file before you
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encrypt your wallet. To do this, close the Bitcoin client and
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copy the wallet.dat file from ~/.bitcoin/ on Linux, /Users/(user
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name)/Application Support/Bitcoin/ on Mac OSX, and %APPDATA%/Bitcoin/
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on Windows (that is /Users/(user name)/AppData/Roaming/Bitcoin on
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Windows Vista and 7 and /Documents and Settings/(user name)/Application
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Data/Bitcoin on Windows XP). Once you have copied that file to a
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safe location, reopen the Bitcoin client and Encrypt your wallet.
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If everything goes fine, delete the backup and enjoy your encrypted
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wallet. Note that once you encrypt your wallet, you will never be
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able to go back to a version of the Bitcoin client older than 0.4.
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Keep in mind that you are always responsible for your own security.
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All it takes is a slightly more advanced wallet-stealing trojan which
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installs a keylogger to steal your wallet passphrase as you enter it
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in addition to your wallet file and you have lost all your Bitcoins.
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Wallet encryption cannot keep you safe if you do not practice
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good security, such as running up-to-date antivirus software, only
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entering your wallet passphrase in the Bitcoin client and using the
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same passphrase only as your wallet passphrase.
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Technical details of wallet encryption
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--------------------------------------
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Wallet encryption uses AES-256-CBC to encrypt only the private keys
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that are held in a wallet. The keys are encrypted with a master key
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which is entirely random. This master key is then encrypted with
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AES-256-CBC with a key derived from the passphrase using SHA512 and
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OpenSSL's EVP_BytesToKey and a dynamic number of rounds determined by
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the speed of the machine which does the initial encryption (and is
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updated based on the speed of a computer which does a subsequent
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passphrase change). Although the underlying code supports multiple
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encrypted copies of the same master key (and thus multiple passphrases)
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the client does not yet have a method to add additional passphrases.
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At runtime, the client loads the wallet as it normally would, however
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the keystore stores the keys in encrypted form. When the passphrase
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is required (to top up keypool or send coins) it will either be queried
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by a GUI prompt, or must first be entered with the walletpassphrase
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RPC command. This will change the wallet to "unlocked" state where the
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unencrypted master key is stored in memory (in the case of GUI, only for
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long enough to complete the requested operation, in RPC, for as long as
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is specified by the second parameter to walletpassphrase). The wallet is
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then locked (or can be manually locked using the walletlock RPC command)
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and the unencrypted master key is removed from memory.
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Implementation details of wallet encryption
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-------------------------------------------
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When the wallet is locked, calls to sendtoaddress, sendfrom, sendmany,
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and keypoolrefill will return Error -13: "Error: Please enter the wallet
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passphrase with walletpassphrase first."
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When the wallet is unlocked, calls to walletpassphrase will fail.
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When a wallet is encrypted, the passphrase is required to top up the
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keypool, thus, if the passphrase is rarely entered, it is possible that
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keypool might run out. In this case, the default key will be used as the
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target for payouts for mining, and calls to getnewaddress and getaccount
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address will return an error. In order to prevent such cases, the keypool
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is automatically refilled when walletpassphrase is called with a correct
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passphrase and when topupkeypool is called (while the wallet is unlocked).
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Note that the keypool continues to be topped up on various occasions when
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a new key from pool is used and the wallet is unlocked (or unencrypted).
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See the documentation at the bitcoin wiki:
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https://en.bitcoin.it/wiki/Main_Page
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... for help and more information.
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