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 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 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 provided data. The data argument should be a binary array that is a mul-
	      tiple 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 identical plain text will produce identical
	      output  when  encrypted with the same key. Any encryption 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 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://sourceforge.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)