'\"
'\" Generated from file 'sha256\&.man' by tcllib/doctools with format 'nroff'
'\" Copyright (c) 2008, Andreas Kupries <andreas_kupries@users\&.sourceforge\&.net>
'\"
.TH "sha256" n 1\&.0\&.4 tcllib "SHA-x Message-Digest Algorithm"
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.BS
.SH NAME
sha256 \- SHA256 Message-Digest Algorithm
.SH SYNOPSIS
package require \fBTcl  8\&.2\fR
.sp
package require \fBsha256  ?1\&.0\&.4?\fR
.sp
\fB::sha2::sha256\fR ?\fB-hex|-bin\fR? [ \fB-channel channel\fR | \fB-file filename\fR | ?\fB--\fR? \fIstring\fR ]
.sp
\fB::sha2::sha224\fR ?\fB-hex|-bin\fR? [ \fB-channel channel\fR | \fB-file filename\fR | ?\fB--\fR? \fIstring\fR ]
.sp
\fB::sha2::hmac\fR \fIkey\fR \fIstring\fR
.sp
\fB::sha2::hmac\fR ?\fB-hex|-bin\fR? \fB-key key\fR [ \fB-channel channel\fR | \fB-file filename\fR | ?\fB--\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 ?\fB-hex|-bin\fR? [ \fB-channel channel\fR | \fB-file filename\fR | ?\fB--\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\&.
.sp
If the \fIstring\fR to hash can be mistaken for an option
(leading dash "-"), use the option \fB--\fR before it to terminate
option processing and force interpretation as a string\&.
.TP
\fB::sha2::sha224\fR ?\fB-hex|-bin\fR? [ \fB-channel channel\fR | \fB-file filename\fR | ?\fB--\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 ?\fB-hex|-bin\fR? \fB-key key\fR [ \fB-channel channel\fR | \fB-file filename\fR | ?\fB--\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\&.
.sp
If the \fIstring\fR to hash can be mistaken for an option
(leading dash "-"), use the option \fB--\fR before it to terminate
option processing and force interpretation as a string\&.
.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
.CS


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

.CE
.CS


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

.CE
.CS


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

.CE
.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 Trackers\fR [http://core\&.tcl\&.tk/tcllib/reportlist]\&.
Please also report any ideas for enhancements you may have for either
package and/or documentation\&.
.PP
When proposing code changes, please provide \fIunified diffs\fR,
i\&.e the output of \fBdiff -u\fR\&.
.PP
Note further that \fIattachments\fR are strongly preferred over
inlined patches\&. Attachments can be made by going to the \fBEdit\fR
form of the ticket immediately after its creation, and then using the
left-most button in the secondary navigation bar\&.
.SH "SEE ALSO"
md4, md5, ripemd128, ripemd160, sha1
.SH KEYWORDS
FIPS 180-1, hashing, message-digest, rfc 2104, security, sha256
.SH CATEGORY
Hashes, checksums, and encryption
.SH COPYRIGHT
.nf
Copyright (c) 2008, Andreas Kupries <andreas_kupries@users\&.sourceforge\&.net>

.fi
