Ubuntu Manpage: sha256 - SHA256 Message-Digest Algorithm

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.

If the string to hash can be mistaken for an option (leading dash "-"), use the
option -- before it to terminate option processing and force interpretation as a
string.

::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.

If the string to hash can be mistaken for an option (leading dash "-"), use the
option -- before it to terminate option processing and force interpretation as a
string.

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  Trackers
       [http://core.tcl.tk/tcllib/reportlist].  Please also report any ideas for enhancements you
       may have for either package and/or documentation.

KEYWORDS

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

COPYRIGHT

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