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NAME

Digest::MD5 - Perl interface to the MD5 Algorithm

SYNOPSIS

# Functional style
use Digest::MD5 qw(md5 md5_hex md5_base64);
$digest = md5($data);
$digest = md5_hex($data);
$digest = md5_base64($data);
# OO style
use Digest::MD5;
$ctx = Digest::MD5->new;
$ctx->add($data);
$ctx->addfile($file_handle);
$digest = $ctx->digest;
$digest = $ctx->hexdigest;
$digest = $ctx->b64digest;

DESCRIPTION

The Digest::MD5 module allows you to use the RSA Data Security Inc. MD5 Message Digest algorithm from within Perl programs. The algorithm takes as input a message of arbitrary length and produces as output a 128-bit "fingerprint" or "message digest" of the input.

Note that the MD5 algorithm is not as strong as it used to be. It has since 2005 been easy to generate different messages that produce the same MD5 digest. It still seems hard to generate messages that produce a given digest, but it is probably wise to move to stronger algorithms for applications that depend on the digest to uniquely identify a message.

The Digest::MD5 module provide a procedural interface for simple use, as well as an object oriented interface that can handle messages of arbitrary length and which can read files directly.

FUNCTIONS

The following functions are provided by the Digest::MD5 module. None of these functions are exported by default.

METHODS

The object oriented interface to Digest::MD5 is described in this section. After a Digest::MD5 object has been created, you will add data to it and finally ask for the digest in a suitable format. A single object can be used to calculate multiple digests.

The following methods are provided:

EXAMPLES

The simplest way to use this library is to import the md5_hex() function (or one of its cousins):

use Digest::MD5 qw(md5_hex);
print "Digest is ", md5_hex("foobarbaz"), "\n";

The above example would print out the message:

Digest is 6df23dc03f9b54cc38a0fc1483df6e21

The same checksum can also be calculated in OO style:

use Digest::MD5;

$md5 = Digest::MD5->new;
$md5->add('foo', 'bar');
$md5->add('baz');
$digest = $md5->hexdigest;

print "Digest is $digest\n";

With OO style, you can break the message arbitrarily. This means that we are no longer limited to have space for the whole message in memory, i.e. we can handle messages of any size.

This is useful when calculating checksum for files:

use Digest::MD5;
my $filename = shift || "/etc/passwd";
open (my $fh, '<', $filename) or die "Can't open '$filename': $!";
binmode($fh);
$md5 = Digest::MD5->new;
while (<$fh>) {
    $md5->add($_);
}
close($fh);
print $md5->b64digest, " $filename\n";

Or we can use the addfile method for more efficient reading of the file:

use Digest::MD5;
my $filename = shift || "/etc/passwd";
open (my $fh, '<', $filename) or die "Can't open '$filename': $!";
binmode ($fh);
print Digest::MD5->new->addfile($fh)->hexdigest, " $filename\n";

Since the MD5 algorithm is only defined for strings of bytes, it can not be used on strings that contains chars with ordinal number above 255 (Unicode strings). The MD5 functions and methods will croak if you try to feed them such input data:

use Digest::MD5 qw(md5_hex);
my $str = "abc\x{300}";
print md5_hex($str), "\n";  # croaks
# Wide character in subroutine entry

What you can do is calculate the MD5 checksum of the UTF-8 representation of such strings. This is achieved by filtering the string through encode_utf8() function:

use Digest::MD5 qw(md5_hex);
use Encode qw(encode_utf8);
my $str = "abc\x{300}";
print md5_hex(encode_utf8($str)), "\n";
# 8c2d46911f3f5a326455f0ed7a8ed3b3

SEE ALSO

Digest, Digest::MD2, Digest::SHA, Digest::HMAC

md5sum(1)

RFC 1321

http://en.wikipedia.org/wiki/MD5

The paper "How to Break MD5 and Other Hash Functions" by Xiaoyun Wang and Hongbo Yu.

COPYRIGHT

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

Copyright 1998-2003 Gisle Aas.
Copyright 1995-1996 Neil Winton.
Copyright 1991-1992 RSA Data Security, Inc.

The MD5 algorithm is defined in RFC 1321. This implementation is derived from the reference C code in RFC 1321 which is covered by the following copyright statement:

This copyright does not prohibit distribution of any version of Perl containing this extension under the terms of the GNU or Artistic licenses.

AUTHORS

The original MD5 interface was written by Neil Winton (N.Winton@axion.bt.co.uk).

The Digest::MD5 module is written by Gisle Aas <gisle@ActiveState.com>.