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 functions.

       ::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 completes 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/fip180-1.htm)

       [2]    Rivest, R., "The MD4 Message Digest Algorithm", RFC 1320, MIT,
              April 1992. (http://www.rfc-editor.org/rfc/rfc1320.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/rfc2104.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://sourceforge.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)
