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blowfish(n)                                 Blowfish Block Cipher                                blowfish(n)



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NAME
       blowfish - Implementation of the Blowfish block cipher

SYNOPSIS
       package require Tcl  8.4

       package require blowfish  ?1.0.4?

       ::blowfish::blowfish ?-mode [ecb|cbc]? ?-dir [encrypt|decrypt]? -key keydata ?-iv vector? ?-out chan-nel? channel?
       nel? ?-chunksize size? ?-pad padchar? [ -in channel | ?--? data ]

       ::blowfish::Init mode keydata iv

       ::blowfish::Encrypt Key data

       ::blowfish::Decrypt Key data

       ::blowfish::Reset Key iv

       ::blowfish::Final Key

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DESCRIPTION
       This package is an implementation in Tcl of the Blowfish algorithm developed by Bruce  Schneier  [1].
       Blowfish is a 64-bit block cipher designed to operate quickly on 32 bit architectures and accepting a
       variable key length. This implementation supports ECB and CBC mode blowfish encryption.

COMMANDS
       ::blowfish::blowfish ?-mode [ecb|cbc]? ?-dir [encrypt|decrypt]? -key keydata ?-iv vector? ?-out chan-nel? channel?
       nel? ?-chunksize size? ?-pad padchar? [ -in channel | ?--? data ]
              Perform the blowfish algorithm on either the data provided by the argument or on the data read
              from  the  -in  channel.  If  an -out channel is given then the result will be written to this
              channel.

              The -key option must be given. This parameter takes a binary string of variable length and  is
              used  to  generate the blowfish key schedule. You should be aware that creating a key schedule
              is quite an expensive operation in blowfish so it is worth reusing the key where possible. See
              Reset.

              The  -mode and -dir options are optional and default to cbc mode and encrypt respectively. The
              initialization vector -iv takes an 8 byte binary argument which  defaults  to  8  zeros.   See
              MODES OF OPERATION for more about available modes and their uses.

              Blowfish is a 64-bit block cipher. This means that the data must be provided in units that are
              a multiple of 8 bytes. The blowfish command will by default add  nul  characters  to  pad  the
              input  data to a multiple of 8 bytes if necessary. The programming api commands will never add
              padding and instead will raise an error if the input is not a multiple of the block size.  The
              -pad  option  can  be  used to change the padding character or to disable padding if the empty
              string is provided as the argument.


PROGRAMMING INTERFACE
       ::blowfish::Init mode keydata iv
              Construct a new blowfish key schedule using the specified key data and the  given  initializa-tion initialization
              tion  vector.  The  initialization  vector  is not used with ECB mode but is important for CBC
              mode.  See MODES OF OPERATION for details about cipher modes.

       ::blowfish::Encrypt Key data
              Use a prepared key acquired by calling Init to encrypt the provided data.  The  data  argument
              should  be  a  binary  array  that is a multiple of the block size of 8 bytes. The result is a
              binary array the same size as the input of encrypted data.

       ::blowfish::Decrypt Key data
              Decipher data using the key. Note that the same key may be used to encrypt  and  decrypt  data
              provided that the initialization vector is reset appropriately for CBC mode.

       ::blowfish::Reset Key iv
              Reset  the  initialization  vector.  This permits the programmer to re-use a key and avoid the
              cost of re-generating the key schedule where the same key data is being used multiple times.

       ::blowfish::Final Key
              This should be called to clean up resources associated with Key.  Once this function has  been
              called the key may not be used again.


MODES OF OPERATION
       Electronic Code Book (ECB)
              ECB is the basic mode of all block ciphers. Each block is encrypted independently and so iden-tical identical
              tical plain text will produce identical output when encrypted with the same key.  Any  encryp-tion encryption
              tion  errors  will  only  affect  a single block however this is vulnerable to known plaintext
              attacks.

       Cipher Block Chaining (CBC)
              CBC mode uses the output of the last block encryption to affect the current block. An initial-ization initialization
              ization  vector  of  the same size as the cipher block size is used to handle the first block.
              The initialization vector should be chosen randomly and transmitted as the first block of  the
              output.  Errors  in  encryption  affect  the  current block and the next block after which the
              cipher will correct itself. CBC is the most commonly used mode in software encryption.


EXAMPLES
       % blowfish::blowfish -hex -mode ecb -dir encrypt -key secret01 "hello, world!"
       d0d8f27e7a374b9e2dbd9938dd04195a


        set Key [blowfish::Init cbc $eight_bytes_key_data $eight_byte_iv]
        append ciphertext [blowfish::Encrypt $Key $plaintext]
        append ciphertext [blowfish::Encrypt $Key $additional_plaintext]
        blowfish::Final $Key


REFERENCES
       [1]    Schneier, B. "Applied Cryptography, 2nd edition", 1996, ISBN 0-471-11709-9, pub. John Wiley  &
              Sons.


AUTHORS
       Frank Pilhofer, Pat Thoyts

BUGS, IDEAS, FEEDBACK
       This  document,  and  the  package  it  describes,  will undoubtedly contain bugs and other problems.
       Please  report  such  in  the  category  blowfish  of  the   Tcllib   SF   Trackers   [http://source-
       forge.net/tracker/?group_id=12883].   Please  also report any ideas for enhancements you may have for
       either package and/or documentation.

SEE ALSO
       3des, des, rc4

KEYWORDS
       block cipher, blowfish, cryptography, encryption, security

COPYRIGHT
       Copyright (c) 2003, Pat Thoyts <patthoyts@users.sourceforge.net>




blowfish                                            1.0.3                                        blowfish(n)