


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


______________________________________________________________________________

NAME
       sha256 - SHA256 Message-Digest Algorithm

SYNOPSIS
       package require Tcl  8.2

       package require sha256  ?1.0.2?

       ::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



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


              as binary data by giving -bin.

              The data to be hashed can be specified either as a string  argu-
              ment  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 applica-
              tions 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  program-
       ming  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  imple-
       mentation  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"



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


              followed by SHA256Update $token "cb". See EXAMPLES.   Note  that
              this  command  is used for both SHA256 and SHA224. Only the ini-
              tialization 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)






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


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>







































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