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September 27, 2011, 03:56:14 PM |
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Technical details of wallet encryption -------------------------------------- Wallet encryption uses AES-256-CBC to encrypt only the private keys that are held in a wallet. The keys are encrypted with a master key which is entirely random. This master key is then encrypted with AES-256-CBC with a key derived from the passphrase using SHA512 and OpenSSL's EVP_BytesToKey and a dynamic number of rounds determined by the speed of the machine which does the initial encryption (and is updated based on the speed of a computer which does a subsequent passphrase change). Although the underlying code supports multiple encrypted copies of the same master key (and thus multiple passphrases) the client does not yet have a method to add additional passphrases.
At runtime, the client loads the wallet as it normally would, however the keystore stores the keys in encrypted form. When the passphrase is required (to top up keypool or send coins) it will either be queried by a GUI prompt, or must first be entered with the walletpassphrase RPC command. This will change the wallet to "unlocked" state where the unencrypted master key is stored in memory (in the case of GUI, only for long enough to complete the requested operation, in RPC, for as long as is specified by the second parameter to walletpassphrase). The wallet is then locked (or can be manually locked using the walletlock RPC command) and the unencrypted master key is removed from memory.
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