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 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 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

CATEGORY
       Hashes, checksums, and encryption

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




blowfish                             1.0.3                         blowfish(n)
