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sha256(n)                              SHA-x Message-Digest Algorithm                              sha256(n)



____________________________________________________________________________________________________________

NAME
       sha256 - SHA256 Message-Digest Algorithm

SYNOPSIS
       package require Tcl  8.2

       package require sha256  ?1.0.3?

       ::sha2::sha256 ?-hex|-bin? [ -channel channel | -file filename | string ]

       ::sha2::sha224 ?-hex|-bin? [ -channel channel | -file filename | string ]

       ::sha2::hmac key string

       ::sha2::hmac ?-hex|-bin? -key key [ -channel channel | -file filename | string ]

       ::sha2::SHA256Init

       ::sha2::SHA224Init

       ::sha2::SHA256Update token data

       ::sha2::SHA256Final token

       ::sha2::SHA224Final token

       ::sha2::HMACInit key

       ::sha2::HMACUpdate token data

       ::sha2::HMACFinal token

____________________________________________________________________________________________________________

DESCRIPTION
       This  package provides an implementation in Tcl of the SHA256 and SHA224 message-digest algorithms as
       specified by FIPS PUB 180-1 (1). These algorithms take a message and generates  a  256-bit  (224-bit)
       digest from the input. The SHA2 algorithms are related to the SHA1 algorithm.

       This  package  also includes support for creating keyed message-digests using the HMAC algorithm from
       RFC 2104 (3) with SHA256 as the message-digest.

COMMANDS
       ::sha2::sha256 ?-hex|-bin? [ -channel channel | -file filename | string ]
              The command takes a message and returns the SHA256 digest of this  message  as  a  hexadecimal
              string. You may request the result as binary data by giving -bin.

              The  data  to be hashed can be specified either as a string argument to the sha256 command, or
              as a filename or a pre-opened channel. If the -filename argument is given  then  the  file  is
              opened,  the  data  read  and hashed and the file is closed. If the -channel argument is given
              then data is read from the channel until the end of file. The channel is not closed. NOTE  use
              of the channel or filename options results in the internal use of vwait. To avoid nested event
              loops in Tk or tclhttpd applications you should  use  the  incremental  programming  API  (see
              below).

              Only one of -file, -channel or string should be given.

       ::sha2::sha224 ?-hex|-bin? [ -channel channel | -file filename | string ]
              Like ::sha2::sha256, except that the SHA224 digest is returned.

       ::sha2::hmac key string

       ::sha2::hmac ?-hex|-bin? -key key [ -channel channel | -file filename | string ]
              Calculate  an  Hashed  Message Authentication digest (HMAC) using the SHA256 digest algorithm.
              HMACs are described in RFC 2104 (3) and provide an SHA256 digest  that  includes  a  key.  All
              options other than -key are as for the ::sha2::sha256 command.


PROGRAMMING INTERFACE
       For  the  programmer,  the  SHA256 hash can be viewed as a bucket into which one pours data. When you
       have finished, you extract a value that is derived from the data that was poured into the bucket. The
       programming  interface  to  the  SHA256 hash operates on a token (equivalent to the bucket). You call
       SHA256Init to obtain a token and then call SHA256Update as many times as required to add data to  the
       hash.  To  release  any resources and obtain the hash value, you then call SHA256Final. An equivalent
       set of functions gives you a keyed digest (HMAC).

       If you have critcl and have built the tcllibc package then the implementation of the hashing function
       will  be  performed  by  compiled  code. Failing that there is a pure-tcl equivalent. The programming
       interface remains the same in all cases.

       ::sha2::SHA256Init

       ::sha2::SHA224Init
              Begins a new SHA256/SHA224 hash. Returns a token ID that must be used for the remaining  func-tions. functions.
              tions.

       ::sha2::SHA256Update token data
              Add  data to the hash identified by token. Calling SHA256Update $token "abcd" is equivalent to
              calling SHA256Update $token "ab" followed by SHA256Update $token  "cb".  See  EXAMPLES.   Note
              that this command is used for both SHA256 and SHA224. Only the initialization and finalization
              commands of both hashes differ.

       ::sha2::SHA256Final token

       ::sha2::SHA224Final token
              Returns the hash value and releases any resources held by this token. Once this  command  com-pletes completes
              pletes  the  token  will be invalid. The result is a binary string of 32/28 bytes representing
              the 256/224 bit SHA256 / SHA224 digest value.

       ::sha2::HMACInit key
              This is equivalent to the ::sha2::SHA256Init command except that it requires the key that will
              be included in the HMAC.

       ::sha2::HMACUpdate token data

       ::sha2::HMACFinal token
              These commands are identical to the SHA256 equivalent commands.


EXAMPLES
       % sha2::sha256 "Tcl does SHA256"
       0b91043ee484abd83c3e4b08d6034d71b937026379f0f59bda6e625e6e214789


       % sha2::hmac Sekret "Tcl does SHA256"
       4f9352c64d655e8a36abe73e6163a9d7a54039877c1c92ec90b07d48d4e854e0


       % set tok [sha2::SHA256Init]
       ::sha2::1
       % sha2::SHA256Update $tok "Tcl "
       % sha2::SHA256Update $tok "does "
       % sha2::SHA256Update $tok "SHA256"
       % sha2::Hex [sha2::SHA256Final $tok]
       0b91043ee484abd83c3e4b08d6034d71b937026379f0f59bda6e625e6e214789


REFERENCES
       [1]    "Secure  Hash  Standard",  National  Institute of Standards and Technology, U.S. Department Of
              Commerce, April 1995.  (http://www.itl.nist.gov/fipspubs/fip18_-1.htm)

       [2]    Rivest, R., "The MD4 Message Digest Algorithm", RFC 1320, MIT,  April  1992.  (http://www .rfc-
              editor.org/rfc/rfc132_.txt

       [3]    Krawczyk,  H.,  Bellare,  M. and Canetti, R. "HMAC: Keyed-Hashing for Message Authentication",
              RFC 2104, February 1997.  (http://www.rfc-editor.org/rfc/rfc21_4.txt)


BUGS, IDEAS, FEEDBACK
       This document, and the package it describes,  will  undoubtedly  contain  bugs  and  other  problems.
       Please   report   such   in   the   category   sha1   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
       md4, md5, ripemd128, ripemd160, sha1

KEYWORDS
       FIPS 180-1, hashing, message-digest, rfc 2104, security, sha256

CATEGORY
       Hashes, checksums, and encryption

COPYRIGHT
       Copyright (c) 2008, Andreas Kupries <andreas_kupries@users.sourceforge.net>




sha1                                                1.0.3                                          sha256(n)