md5 - MD5 Message-Digest Algorithm
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 can be used to accelerate the digest computation. If no suitable compiled package is available then the pure-Tcl implementation wil be 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.
Calculate the MD5 digest of the 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.
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.
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).
Begins a new MD5 hash. Returns a token ID that must be used for the remaining functions.
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.
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.
This is equivalent to the ::md5::MD5Init command except that it requires the key that will be included in the HMAC.
These commands are identical to the MD5 equivalent commands.
% 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
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)
Rivest, R., "The MD4 Message Digest Algorithm", RFC 1320, MIT, April 1992. (http://www.rfc-editor.org/rfc/rfc1320.txt)
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)
This document, and the package it describes, will undoubtedly contain bugs and other problems. Please report such in the category md5 of the Tcllib SF Trackers. Please also report any ideas for enhancements you may have for either package and/or documentation.
Hashes, checksums, and encryption
Copyright © 2003, Pat Thoyts <email@example.com>