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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_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 3-element list: number of blocks processed, a
           16-byte internal state buffer, then up to 63 bytes of unprocessed
           data.  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(3), Digest::MD2(3), Digest::SHA(3), Digest::HMAC(3)

       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:

       o   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 v5.24.0                      2016-03-01                  Digest::MD5(3pm)

perl 5.24 - Generated Sun Nov 6 07:17:19 CST 2016
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