This page describes md5, a command line utility usable on either Unix or MS-DOS/Windows, which generates and verifies message digests (digital signatures) using the MD5 algorithm. This program can be useful when developing shell scripts or Perl programs for software installation, file comparison, and detection of file corruption and tampering.
Many older programs requiring digital signatures employed 16 or 32 bit cyclical redundancy codes (CRC) originally developed to verify correct transmission in data communication protocols, but these short codes, while adequate to detect the kind of transmission errors for which they were intended, are insufficiently secure for applications such as electronic commerce and verification of security related software distributions.
The most commonly used present-day message digest algorithm is the 128 bit MD5 algorithm, developed by Ron Rivest of the MIT Laboratory for Computer Science and RSA Data Security, Inc. The algorithm, with a reference implementation, was published as Internet RFC 1321 in April 1992, and was placed into the public domain at that time. Message digest algorithms such as MD5 are not deemed "encryption technology" and are not subject to the export controls some governments impose on other data security products. (Obviously, the responsibility for obeying the laws in the jurisdiction in which you reside is entirely your own, but many common Web and Mail utilities use MD5, and I am unaware of any restrictions on their distribution and use.)
The MD5 algorithm has been implemented in numerous computer languages including C, Perl, and Java; if you're writing a program in such a language, track down a suitable subroutine and incorporate it into your program. The program described on this page is a command line implementation of MD5, intended for use in shell scripts and Perl programs (it is much faster than computing an MD5 signature directly in Perl). This md5 program was originally developed as part of a suite of tools intended to monitor large collections of files (for example, the contents of a Web site) to detect corruption of files and inadvertent (or perhaps malicious) changes. That task is now best accomplished with more comprehensive packages such as Tripwire, but the command line md5 component continues to prove useful for verifying correct delivery and installation of software packages, comparing the contents of two different systems, and checking for changes in specific files.
This program has not been tested on a machine on which int and/or long are longer than 32 bits.
md5.exe
(compiled using Microsoft Visual C++ 5.0),
and in source code form along with a
Makefile
to build the program under Unix.
This software is in the public domain. Permission to use, copy, modify, and distribute this software and its documentation for any purpose and without fee is hereby granted, without any conditions or restrictions. This software is provided "as is" without express or implied warranty.