243 lines
9.3 KiB
HTML
243 lines
9.3 KiB
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
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"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
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<title>MD5: Command Line Message Digest Utility</title>
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<meta name="author" content="John Walker" />
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<meta name="description" content="MD5: Command Line Message Digest Utility" />
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<meta name="keywords" content="md5, message, digest, signature, command, line, utility" />
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<meta name="robots" content="index" />
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<style type="text/css">
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dd {
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dt {
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margin-top: 1ex;
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}
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</style>
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</head>
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<body class="standard">
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<center>
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<h1><img src="md5.png" width="208" height="109" alt="MD5" /></h1>
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<h2>
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Command Line Message Digest Utility
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</h2>
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</center>
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<hr />
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<p class="j">
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This page describes <b>md5</b>, a command line utility usable on
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either Unix or MS-DOS/Windows, which generates and verifies
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message digests (digital signatures) using the MD5 algorithm.
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This program can be useful when developing shell scripts or Perl
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programs for software installation, file comparison, and
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detection of file corruption and tampering.
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</p>
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<h3>NAME</h3>
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<b>md5</b> - generate / check MD5 message digest
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<h3>SYNOPSIS</h3>
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<b>md5</b> [ <b>-c</b><i>signature</i> ]
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[ <b>-l</b> ] [ <b>-n</b> ]
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[ <b>-u</b> ] [ <b>-v</b> ]
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[ <b>-d</b><i>input_text</i> | <em>infile</em>… ]
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<h3>DESCRIPTION</h3>
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<p class="j">
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A <em>message digest</em> is a compact digital signature for an
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arbitrarily long stream of binary data. An ideal message digest
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algorithm would never generate the same signature for two
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different sets of input, but achieving such theoretical
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perfection would require a message digest as long as the input
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file. Practical message digest algorithms compromise in favour
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of a digital signature of modest size created with an algorithm
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designed to make preparation of input text with a given
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signature computationally infeasible. Message digest algorithms
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have much in common with techniques used in encryption, but to a
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different end; verification that data have not been altered
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since the signature was published.
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</p>
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<p class="j">
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Many older programs requiring digital signatures employed 16 or
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32 bit <em>cyclical redundancy codes</em> (CRC) originally
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developed to verify correct transmission in data communication
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protocols, but these short codes, while adequate to detect the
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kind of transmission errors for which they were intended, are
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insufficiently secure for applications such as electronic
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commerce and verification of security related software
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distributions.
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</p>
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<p class="j">
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The most commonly used present-day message digest algorithm is
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the 128 bit MD5 algorithm, developed by Ron Rivest of the
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<a href="http://web.mit.edu/" target="_blank">MIT</a>
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<a href="http://www.lcs.mit.edu/" target="_blank">Laboratory for Computer Science</a> and
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<a href="http://www.rsa.com/" target="_blank">RSA Data Security,
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Inc.</a> The algorithm, with a reference implementation, was
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published as Internet <a href="rfc1321.html">RFC 1321</a> in April 1992, and was
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placed into the public domain at that time. Message
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digest algorithms such as MD5 are not deemed
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“encryption technology” and are not subject to the
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export controls some governments impose on
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other data security products. (Obviously, the
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responsibility for obeying the laws in the jurisdiction
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in which you reside is entirely your own, but many
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common Web and Mail utilities use MD5, and I am unaware
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of any restrictions on their distribution and use.)
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</p>
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<p class="j">
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The MD5 algorithm has been implemented in numerous
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computer languages including C,
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<a href="http://www.perl.org/" target="_blank">Perl</a>, and
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<a href="http://java.sun.com/" target="_blank">Java</a>; if you're
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writing a program in such a language, track down a suitable
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subroutine and incorporate it into your program. The
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program described on this page is a <em>command line</em>
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implementation of MD5, intended for use in shell scripts
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and Perl programs (it is much faster than computing
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an MD5 signature directly in Perl). This <b>md5</b>
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program was originally developed as part of a suite of tools
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intended to monitor large collections of files (for example,
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the contents of a Web site) to detect corruption of
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files and inadvertent (or perhaps malicious) changes. That
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task is now best accomplished with more comprehensive
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packages such as
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<a href="http://www.tripwire.com/" target="_blank">Tripwire</a>,
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but the command line <b>md5</b> component continues to prove useful
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for verifying correct delivery and installation of software packages,
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comparing the contents of two different systems, and checking for
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changes in specific files.
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</p>
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<h3>OPTIONS</h3>
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<dl>
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<dt><b>-c</b><i>signature</i></dt> <dd>Computes the signature of the
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specified <em>infile</em> or the string supplied by the <b>-d</b>
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option and compares it against the specified <i>signature</i>.
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If the two signatures match, the exit status will be zero,
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otherwise the exit status will be 1. No signature is written;
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only the exit
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status is set. The signature to be checked must be specified
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as 32 hexadecimal digits.</dd>
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<dt><b>-d</b><i>input_text</i></dt> <dd>A signature is computed for the
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given <i>input_text</i> (which must be quoted if it contains white space
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characters) instead of input from <i>infile</i> or standard
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input. If input is specified with the <b>-d</b> option, no
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<i>infile</i> should be specified.</dd>
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<dt><b>-l</b></dt> <dd>Use lower case letters for hexadecimal
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digits “a” through “f”. By default, upper case letters are
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used. Note that the <i>signature</i> argument to the
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<b>-c</b> option may use upper or lower case hexadecimal
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digits (or a mix) regardless of the setting of this option.</dd>
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<dt><b>-n</b></dt> <dd>Suppress printing the file name (or
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“<tt>-</tt>” for standard input) after the hexadecimal
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signature.</dd>
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<dt><b>-o</b><i>fname</i></dt> <dd>Write output to <i>fname</i>.
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If <i>fname</i> is “<tt>-</tt>”, output is written
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to standard output, which is the default is no
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<b>-o</b> option is specified.</dd>
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<dt><b>-u</b></dt> <dd>Print how-to-call information.</dd>
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<dt><b>-v</b></dt> <dd>Print version information.</dd>
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</dl>
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<h3>FILES</h3>
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<p class="j">
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If no <em>infile</em> or <b>-d</b> option is specified or
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<em>infile</em> is a single “<tt>-</tt>”, <b>md5</b>
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reads from standard input. A single “<tt>-</tt>” on
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the command line causes all subsequent arguments to be treated as
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file names even if they begin with “<tt>-</tt>”. If
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no <b>-o</b> option is specified or the <em>fname</em> is a
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single “<tt>-</tt>”, output is sent to standard
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output. Input and output are processed strictly serially;
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consequently <b>md5</b> may be used in pipelines.
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</p>
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<h3>BUGS</h3>
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<p class="j">
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The mechanism used to set standard input to binary mode may be
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specific to Microsoft C; if you rebuild the DOS/Windows version
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of the program from source using another compiler, be sure to verify
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binary files work properly when read via redirection or a pipe.
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</p>
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<p class="j">
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This program has not been tested on a machine on which <tt>int</tt>
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and/or <tt>long</tt> are longer than 32 bits.
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</p>
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<h2><img src="/images/icons/file.png" alt="" align="middle" width="40" height="40" />
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Download <a href="md5.zip">md5.zip</a> (Zipped)
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or <a href="md5.tar.gz">md5.tar.gz</a> (tar/gzip)</h2>
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<p class="j">
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The program is provided as either <a href="md5.zip">md5.zip</a>, a
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<a href="http://www.info-zip.org/" target="_blank">Zipped</a> archive, or
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<a href="md5.tar.gz">md5.tar.gz</a>, a <tt>gzip</tt>ped
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<tt>tar</tt> archive. The two archive formats have identical
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contents; both include a
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ready-to-run Win32 command-line executable program, <code>md5.exe</code>
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(compiled using Microsoft Visual C++ .NET),
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and source code along with a
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<code>Makefile</code> to build the program under Unix.
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</p>
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<h3>SEE ALSO</h3>
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<b>sum</b>(1)
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<h3>EXIT STATUS</h3>
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<p class="j">
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<b>md5</b> returns status 0 if processing was
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completed without errors, 1 if the <b>-c</b> option was
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specified and the given signature does not match that of the input,
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and 2 if processing could not be performed at
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all due, for example, to a nonexistent input file.
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</p>
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<h3>COPYING</h3>
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<blockquote>
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<p class="j">
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This software is in the public domain. Permission to use, copy,
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modify, and distribute this software and its documentation for
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any purpose and without fee is hereby granted, without any
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conditions or restrictions. This software is provided “as is”
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without express or implied warranty.
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</p>
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</blockquote>
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<h3>ACKNOWLEDGEMENTS</h3>
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<p class="j">
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The MD5 algorithm was developed by Ron Rivest. The public
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domain C language implementation used in this program was
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written by Colin Plumb in 1993.
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</p>
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<h3><a href="/">Fourmilab home page</a></h3>
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<hr />
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<address>
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<a href="/">by John Walker</a><br />
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January 14th, 2008
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</address>
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</body>
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</html>
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