


blowfish(n)           Blowfish Block Cipher           blowfish(n)


______________________________________________________________________________

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 channel? ?-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

_________________________________________________________________

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 channel? ?-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



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blowfish(n)           Blowfish Block Cipher           blowfish(n)


              be provided in units that are a multiple of 8 bytes.  The  blow-
              fish 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  initialization 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 pro-
              vided 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 sched-
              ule 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 identical plain text will produce
              identical output when encrypted with the same key.  Any  encryp-
              tion errors will only affect a single block however this is vul-
              nerable to known plaintext attacks.

       Cipher Block Chaining (CBC)
              CBC mode uses the output of the last block encryption to  affect
              the  current block. An initialization 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



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blowfish(n)           Blowfish Block Cipher           blowfish(n)


              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

CATEGORY
       Hashes, checksums, and encryption

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

















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