Ubuntu Manpage: sha256 - SHA256 Message-Digest Algorithm

NAME

       sha256 - SHA256 Message-Digest Algorithm

SYNOPSIS

       package require Tcl 8.5 9

       package require sha256 ?1.0.6?

       ::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.

       BEWARE  The  commands  in  this package expect binary data as their input.  When a -file is provided then
       this is ensured by the commands themselves, as they open  the  referenced  file  in  binary  mode.   When
       literal  data,  or a -channel are provided instead, then the command's caller is responsible for ensuring
       this fact.  The necessary conversion command is encoding convertto utf-8 $string.

       ATTENTION, there is a Tcl 9 COMPATIBILITY ISSUE here.

       Tcl 8.x silently mishandles non-binary input by cutting it internally to size. I.e. by only using the low
       byte of a higher unicode point.  No error is thrown, the result is simply wrong.

       Tcl 9 throws an error instead, i.e.

              expected byte sequence but character <location> was ...

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.

       When proposing code changes, please provide unified diffs, i.e the output of diff -u.

       Note  further  that  attachments  are strongly preferred over inlined patches. Attachments can be made by
       going to the Edit form of the ticket immediately after its creation, and then using the left-most  button
       in the secondary navigation bar.

KEYWORDS

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

COPYRIGHT

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

tcllib                                                1.0.6                                         sha256(3tcl)