NAME¶

md5 - MD5 Message-Digest Algorithm

SYNOPSIS¶

package require Tcl 8.5 9

package require md5 ?2.0.9?

::md5::md5 ?-hex? [ -channel channel | -file filename | string ]

::md5::hmac ?-hex? -key key [ -channel channel | -file filename | string ]

::md5::MD5Init

::md5::MD5Update token data

::md5::MD5Final token

::md5::HMACInit key

::md5::HMACUpdate token data

::md5::HMACFinal token

DESCRIPTION¶

This package is an implementation in Tcl of the MD5 message-digest algorithm as described in RFC 1321 (1). This algorithm takes an arbitrary quantity of data and generates a 128-bit message digest from the input. The MD5 algorithm is related to the MD4 algorithm (2) but has been strengthened against certain types of potential attack. MD5 should be used in preference to MD4 for new applications.

If you have critcl and have built the tcllibc package then the implementation of the hashing function will be performed by compiled code. Alternatively if you have either cryptkit or Trf then either of these is used to accelerate the digest computation. If no suitable compiled package is available then the pure-Tcl implementation is used. The programming interface remains the same in all cases.

Note the previous version of this package always returned a hex encoded string. This has been changed to simplify the programming interface and to make this version more compatible with other implementations. To obtain the previous usage, either explicitly specify package version 1 or use the -hex option to the md5 command.

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¶

::md5::md5 ?-hex? [ -channel channel | -file filename | string ]

Calculate the MD5 digest of the binary data given in string. This is returned as a binary string by default. Giving the -hex option will return a hexadecimal encoded version of the digest.

The data to be hashed can be specified either as a string argument to the md5 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.

Only one of -file, -channel or string should be given.

::md5::hmac ?-hex? -key key [ -channel channel | -file filename | string ]

Calculate an Hashed Message Authentication digest (HMAC) using the MD5 digest algorithm. HMACs are described in RFC 2104 (3) and provide an MD5 digest that includes a key. All options other than -key are as for the ::md5::md5 command.

PROGRAMMING INTERFACE¶

For the programmer, the MD5 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 MD5 hash operates on a token (equivalent to the bucket). You call MD5Init to obtain a token and then call MD5Update as many times as required to add data to the hash. To release any resources and obtain the hash value, you then call MD5Final. An equivalent set of functions gives you a keyed digest (HMAC).

::md5::MD5Init

Begins a new MD5 hash. Returns a token ID that must be used for the remaining functions.

::md5::MD5Update token data

Add data to the hash identified by token. Calling MD5Update $token "abcd" is equivalent to calling MD5Update $token "ab" followed by MD5Update $token "cb". See EXAMPLES.

::md5::MD5Final 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 16 bytes representing the 128 bit MD5 digest value.

::md5::HMACInit key

This is equivalent to the ::md5::MD5Init command except that it requires the key that will be included in the HMAC.

::md5::HMACUpdate token data

::md5::HMACFinal token

These commands are identical to the MD5 equivalent commands.

EXAMPLES¶

% md5::md5 -hex "Tcl does MD5"
8AAC1EE01E20BB347104FABB90310433

% md5::hmac -hex -key Sekret "Tcl does MD5"
35BBA244FD56D3EDF5F3C47474DACB5D

% set tok [md5::MD5Init]
::md5::1
% md5::MD5Update $tok "Tcl "
% md5::MD5Update $tok "does "
% md5::MD5Update $tok "MD5"
% md5::Hex [md5::MD5Final $tok]
8AAC1EE01E20BB347104FABB90310433

REFERENCES¶

[1]

Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321, MIT and RSA Data Security, Inc, April 1992. (http://www.rfc-editor.org/rfc/rfc1321.txt)

[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 md5 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.

SEE ALSO¶

md4, sha1

KEYWORDS¶

hashing, md5, message-digest, rfc 1320, rfc 1321, rfc 2104, security

CATEGORY¶

Hashes, checksums, and encryption

COPYRIGHT¶

Copyright (c) 2003, Pat Thoyts <patthoyts@users.sourceforge.net>