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From Apache subversion Wiki <comm...@subversion.apache.org>
Subject [Subversion Wiki] Update of "MasterPassphrase" by GregStein
Date Mon, 26 Mar 2012 16:10:18 GMT
Dear Wiki user,

You have subscribed to a wiki page or wiki category on "Subversion Wiki" for change notification.

The "MasterPassphrase" page has been changed by GregStein:
http://wiki.apache.org/subversion/MasterPassphrase?action=diff&rev1=17&rev2=18

Comment:
clarify that the prefix applies to the plaintext, before encryption

  
  The passwords will be encrypted using [[http://en.wikipedia.org/wiki/Advanced_Encryption_Standard|AES-256]]
in [[http://en.wikipedia.org/wiki/Block_cipher_modes_of_operation#Cipher-block_chaining_.28CBC.29|CBC
mode]]. This is a block-oriented, symmetric cipher (16 byte blocks), so some padding will
be added/stripped to the plaintext password (a NUL character is fine).
  
- To prevent dictionary attacks against the encrypted passwords, they will be prefixed with
4 bytes (32 bits) of random data.
+ To prevent dictionary attacks against the encrypted passwords, the plaintext password will
be prefixed with 4 bytes (32 bits) of random data before encryption.
  
  The encryption algorithm requires a 16 byte key (technically, it can also be 24 or 32 bytes),
and a 16 byte [[http://en.wikipedia.org/wiki/Initialization_vector|initialization vector]].
The crypt key will be constructed as a derivation of the master password (see [[http://en.wikipedia.org/wiki/PBKDF2|PBKDF2]]).
PBKDF2 requires a 64 bit salt. The IV is a random 16 byte value. The salt and IV will be stored
within the block of data encrypted by the master password. The master password decrypts that
data block, uses the salt to generate the (de)crypt key, then pairs it with the IV to decrypt
the target password.
  

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