Digest::MD5(3pm) Perl Programmers Reference Guide Digest::MD5(3pm)
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);
$digest = $ctx->digest;
$digest = $ctx->hexdigest;
$digest = $ctx->b64digest;
DESCRIPTION
The "Digest::MD5" module allows you to use the RSA Data Security Inc. MD5 Message Digest algorithm
from within Perl programs. The algorithm takes as input a message of arbitrary length and produces
as output a 128-bit "fingerprint" or "message digest" of the input.
Note that the MD5 algorithm is not as strong as it used to be. It has since 2005 been easy to gener-ate generate
ate different messages that produce the same MD5 digest. It still seems hard to generate messages
that produce a given digest, but it is probably wise to move to stronger algorithms for applications
that depend on the digest to uniquely identify a message.
The "Digest::MD5" module provide a procedural interface for simple use, as well as an object oriented
interface that can handle messages of arbitrary length and which can read files directly.
FUNCTIONS
The following functions are provided by the "Digest::MD5" module. None of these functions are
exported by default.
md5($data,...)
This function will concatenate all arguments, calculate the MD5 digest of this "message", and
return it in binary form. The returned string will be 16 bytes long.
The result of md5("a", "b", "c") will be exactly the same as the result of md5("abc").
md5_hex($data,...)
Same as md5(), but will return the digest in hexadecimal form. The length of the returned string
will be 32 and it will only contain characters from this set: '0'..'9' and 'a'..'f'.
md5_base64($data,...)
Same as md5(), but will return the digest as a base64 encoded string. The length of the returned
string will be 22 and it will only contain characters from this set: 'A'..'Z', 'a'..'z',
'0'..'9', '+' and '/'.
Note that the base64 encoded string returned is not padded to be a multiple of 4 bytes long. If
you want interoperability with other base64 encoded md5 digests you might want to append the
redundant string "==" to the result.
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:
$md5 = Digest::MD5->new
The constructor returns a new "Digest::MD5" object which encapsulate the state of the MD5 mes-sage-digest message-digest
sage-digest algorithm.
If called as an instance method (i.e. $md5->new) it will just reset the state the object to the
state of a newly created object. No new object is created in this case.
$md5->reset
This is just an alias for $md5->new.
$md5->clone
This a copy of the $md5 object. It is useful when you do not want to destroy the digests state,
but need an intermediate value of the digest, e.g. when calculating digests iteratively on a con-tinuous continuous
tinuous data stream. Example:
my $md5 = Digest::MD5->new;
while (<>) {
$md5->add($_);
print "Line $.: ", $md5->clone->hexdigest, "\n";
}
$md5->add($data,...)
The $data provided as argument are appended to the message we calculate the digest for. The
return value is the $md5 object itself.
All these lines will have the same effect on the state of the $md5 object:
$md5->add("a"); $md5->add("b"); $md5->add("c");
$md5->add("a")->add("b")->add("c");
$md5->add("a", "b", "c");
$md5->add("abc");
$md5->addfile($io_handle)
The $io_handle will be read until EOF and its content appended to the message we calculate the
digest for. The return value is the $md5 object itself.
The addfile() method will croak() if it fails reading data for some reason. If it croaks it is
unpredictable what the state of the $md5 object will be in. The addfile() method might have been
able to read the file partially before it failed. It is probably wise to discard or reset the
$md5 object if this occurs.
In most cases you want to make sure that the $io_handle is in "binmode" before you pass it as
argument to the addfile() method.
$md5->add_bits($data, $nbits)
$md5->add_bits($bitstring)
Since the MD5 algorithm is byte oriented you might only add bits as multiples of 8, so you proba-bly probably
bly want to just use add() instead. The add_bits() method is provided for compatibility with
other digest implementations. See Digest for description of the arguments that add_bits() take.
$md5->digest
Return the binary digest for the message. The returned string will be 16 bytes long.
Note that the "digest" operation is effectively a destructive, read-once operation. Once it has
been performed, the "Digest::MD5" object is automatically "reset" and can be used to calculate
another digest value. Call $md5->clone->digest if you want to calculate the digest without
resetting the digest state.
$md5->hexdigest
Same as $md5->digest, but will return the digest in hexadecimal form. The length of the returned
string will be 32 and it will only contain characters from this set: '0'..'9' and 'a'..'f'.
$md5->b64digest
Same as $md5->digest, but will return the digest as a base64 encoded string. The length of the
returned string will be 22 and it will only contain characters from this set: 'A'..'Z', 'a'..'z',
'0'..'9', '+' and '/'.
The base64 encoded string returned is not padded to be a multiple of 4 bytes long. If you want
interoperability with other base64 encoded md5 digests you might want to append the string "=="
to the result.
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 arbitrary. 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 $file = shift || "/etc/passwd";
open(FILE, $file) or die "Can't open '$file': $!";
binmode(FILE);
$md5 = Digest::MD5->new;
while (<FILE>) {
$md5->add($_);
}
close(FILE);
print $md5->b64digest, " $file\n";
Or we can use the addfile method for more efficient reading of the file:
use Digest::MD5;
my $file = shift || "/etc/passwd";
open(FILE, $file) or die "Can't open '$file': $!";
binmode(FILE);
print Digest::MD5->new->addfile(*FILE)->hexdigest, " $file\n";
Perl 5.8 support Unicode characters in strings. 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. 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::SHA1, 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:
Copyright (C) 1991-2, RSA Data Security, Inc. Created 1991. All rights reserved.
License to copy and use this software is granted provided that it is identified as the "RSA Data
Security, Inc. MD5 Message-Digest Algorithm" in all material mentioning or referencing this soft-
ware or this function.
License is also granted to make and use derivative works provided that such works are identified
as "derived from the RSA Data Security, Inc. MD5 Message-Digest Algorithm" in all material men-
tioning or referencing the derived work.
RSA Data Security, Inc. makes no representations concerning either the merchantability of this
software or the suitability of this software for any particular purpose. It is provided "as is"
without express or implied warranty of any kind.
These notices must be retained in any copies of any part of this documentation and/or software.
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>.
perl v5.8.8 2001-09-21 Digest::MD5(3pm)
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