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Digest::MD5(3)	       Perl Programmers Reference Guide		Digest::MD5(3)

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::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:

       ยท   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>.

perl v5.10.0			  2007-12-18			Digest::MD5(3)
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