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 = $ctx->b64digest;
DESCRIPTION¶
The "Digest::MD5" module allows you to use the RSA Data Security Inc.
MD5 Message Digest algorithm from within Perl programs. The algorithm takes as
input a message of arbitrary length and produces as output a 128-bit
"fingerprint" or "message digest" of the input.
Note that the MD5 algorithm is not as strong as it used to be. It has since 2005
been easy to generate different messages that produce the same MD5 digest. It
still seems hard to generate messages that produce a given digest, but it is
probably wise to move to stronger algorithms for applications that depend on
the digest to uniquely identify a message.
The "Digest::MD5" module provide a procedural interface for simple
use, as well as an object oriented interface that can handle messages of
arbitrary length and which can read files directly.
FUNCTIONS¶
The following functions are provided by the "Digest::MD5" module. None
of these functions are exported by default.
- md5($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 message-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 continuous 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 probably 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::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:
- •
- 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 software 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 mentioning 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>.