Ubuntu Manpage: Digest::MD5 - Perl interface to the MD5 Algorithm

Provided by: perl-doc_5.26.1-6ubuntu0.7_all

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

COPYRIGHT

This library is free software; you can redistribute it and/or modify it under the same terms as Perl
itself.

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:

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>.