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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
	      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
	      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>

blowfish			     1.0.3			   blowfish(n)
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