'\"
'\" Generated from file '/usr/obj/ports/tcllib-1.11.1/tcllib-1.11.1/modules/sha1/sha256.man' by tcllib/doctools with format 'nroff'
'\" Copyright (c) 2008, Andreas Kupries <andreas_kupries@users.sourceforge.net>
'\"
'\" The definitions below are for supplemental macros used in Tcl/Tk
'\" manual entries.
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'\" .AP type name in/out ?indent?
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\\$1\l'|0\(ul'\\$2
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.TH "sha256" n 1.0.2 sha1 "SHA-x Message-Digest Algorithm"
.BS
.SH NAME
sha256 \- SHA256 Message-Digest Algorithm
.SH SYNOPSIS
package require \fBTcl  8.2\fR
.sp
package require \fBsha256  ?1.0.2?\fR
.sp
\fB::sha2::sha256\fR ?\fI-hex|-bin\fR? [ \fI-channel channel\fR | \fI-file filename\fR | \fIstring\fR ]
.sp
\fB::sha2::sha224\fR ?\fI-hex|-bin\fR? [ \fI-channel channel\fR | \fI-file filename\fR | \fIstring\fR ]
.sp
\fB::sha2::hmac\fR \fIkey\fR \fIstring\fR
.sp
\fB::sha2::hmac\fR ?\fI-hex|-bin\fR? \fI-key key\fR [ \fI-channel channel\fR | \fI-file filename\fR | \fIstring\fR ]
.sp
\fB::sha2::SHA256Init\fR
.sp
\fB::sha2::SHA224Init\fR
.sp
\fB::sha2::SHA256Update\fR \fItoken\fR \fIdata\fR
.sp
\fB::sha2::SHA256Final\fR \fItoken\fR
.sp
\fB::sha2::SHA224Final\fR \fItoken\fR
.sp
\fB::sha2::HMACInit\fR \fIkey\fR
.sp
\fB::sha2::HMACUpdate\fR \fItoken\fR \fIdata\fR
.sp
\fB::sha2::HMACFinal\fR \fItoken\fR
.sp
.BE
.SH DESCRIPTION
.PP
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.
.PP
This package also includes support for creating keyed message-digests
using the HMAC algorithm from RFC 2104 (3) with SHA256 as the
message-digest.
.SH COMMANDS
.TP
\fB::sha2::sha256\fR ?\fI-hex|-bin\fR? [ \fI-channel channel\fR | \fI-file filename\fR | \fIstring\fR ]
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 \fI-bin\fR.
.sp
The data to be hashed can be specified either as a string argument to
the \fBsha256\fR command, or as a filename or a pre-opened channel. If the
\fI-filename\fR argument is given then the file is opened, the data read
and hashed and the file is closed. If the \fI-channel\fR argument is
given then data is read from the channel until the end of file. The
channel is not closed. \fINOTE\fR use of the channel or filename
options results in the internal use of \fBvwait\fR. To avoid nested
event loops in Tk or tclhttpd applications you should use the
incremental programming API (see below).
.sp
Only one of \fI-file\fR, \fI-channel\fR or \fIstring\fR should be given.
.TP
\fB::sha2::sha224\fR ?\fI-hex|-bin\fR? [ \fI-channel channel\fR | \fI-file filename\fR | \fIstring\fR ]
Like \fB::sha2::sha256\fR, except that the SHA224 digest is returned.
.TP
\fB::sha2::hmac\fR \fIkey\fR \fIstring\fR
.TP
\fB::sha2::hmac\fR ?\fI-hex|-bin\fR? \fI-key key\fR [ \fI-channel channel\fR | \fI-file filename\fR | \fIstring\fR ]
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
\fI-key\fR are as for the \fB::sha2::sha256\fR command.
.PP
.SH "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 \fBSHA256Init\fR to obtain a
token and then call \fBSHA256Update\fR as many times as required to
add data to the hash. To release any resources and obtain the hash
value, you then call \fBSHA256Final\fR. An equivalent set of
functions gives you a keyed digest (HMAC).
.PP
If you have \fBcritcl\fR and have built the \fBtcllibc\fR
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.
.TP
\fB::sha2::SHA256Init\fR
.TP
\fB::sha2::SHA224Init\fR
Begins a new SHA256/SHA224 hash. Returns a token ID that must be used
for the remaining functions.
.TP
\fB::sha2::SHA256Update\fR \fItoken\fR \fIdata\fR
Add data to the hash identified by token. Calling
\fISHA256Update $token "abcd"\fR is equivalent to calling
\fISHA256Update $token "ab"\fR followed by
\fISHA256Update $token "cb"\fR. See \fBEXAMPLES\fR.
Note that this command is used for both SHA256 and SHA224. Only the
initialization and finalization commands of both hashes differ.
.TP
\fB::sha2::SHA256Final\fR \fItoken\fR
.TP
\fB::sha2::SHA224Final\fR \fItoken\fR
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.
.TP
\fB::sha2::HMACInit\fR \fIkey\fR
This is equivalent to the \fB::sha2::SHA256Init\fR command except
that it requires the key that will be included in the HMAC.
.TP
\fB::sha2::HMACUpdate\fR \fItoken\fR \fIdata\fR
.TP
\fB::sha2::HMACFinal\fR \fItoken\fR
These commands are identical to the SHA256 equivalent commands.
.PP
.SH EXAMPLES
.nf

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

.fi
.nf

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

.fi
.nf

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

.fi
.SH REFERENCES
.IP [1]
"Secure Hash Standard", National Institute of Standards
and Technology, U.S. Department Of Commerce, April 1995.
(\fIhttp://www.itl.nist.gov/fipspubs/fip180-1.htm\fR)
.IP [2]
Rivest, R., "The MD4 Message Digest Algorithm", RFC 1320, MIT,
April 1992. (\fIhttp://www.rfc-editor.org/rfc/rfc1320.txt\fR)
.IP [3]
Krawczyk, H., Bellare, M. and Canetti, R. "HMAC: Keyed-Hashing for
Message Authentication", RFC 2104, February 1997.
(\fIhttp://www.rfc-editor.org/rfc/rfc2104.txt\fR)
.PP
.SH "BUGS, IDEAS, FEEDBACK"
This document, and the package it describes, will undoubtedly contain
bugs and other problems.
Please report such in the category \fIsha1\fR of the
\fITcllib SF Trackers\fR [http://sourceforge.net/tracker/?group_id=12883].
Please also report any ideas for enhancements you may have for either
package and/or documentation.
.SH "SEE ALSO"
md4, md5, ripemd128, ripemd160, sha1
.SH KEYWORDS
FIPS 180-1, hashing, message-digest, rfc 2104, security, sha256
.SH COPYRIGHT
.nf
Copyright (c) 2008, Andreas Kupries <andreas_kupries@users.sourceforge.net>

.fi