Digest::MD5(3perl) Perl Programmers Reference Guide Digest::MD5(3perl)
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 = $ctx->b64digest;
DESCRIPTION
The "Digest::MD5" module allows you to use the RSA Data Security Inc.
MD5 Message Digest algorithm from within Perl programs. The algorithm
takes as input a message of arbitrary length and produces as output a
128-bit "fingerprint" or "message digest" of the input.
Note that the MD5 algorithm is not as strong as it used to be. It has
since 2005 been easy to generate different messages that produce the
same MD5 digest. It still seems hard to generate messages that produce
a given digest, but it is probably wise to move to stronger algorithms
for applications that depend on the digest to uniquely identify a
message.
The "Digest::MD5" module provide a procedural interface for simple use,
as well as an object oriented interface that can handle messages of
arbitrary length and which can read files directly.
FUNCTIONS
The following functions are provided by the "Digest::MD5" module. None
of these functions are exported by default.
md5($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.
@ctx = $md5->context
$md5->context(@ctx)
Saves or restores the internal state. When called with no
arguments, returns a list: number of blocks processed, a 16-byte
internal state buffer, then optionally up to 63 bytes of unprocessed
data if there are any. When passed those same arguments, restores
the state. This is only useful for specialised operations.
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:
• 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>.
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