MAN page from OpenSuSE perl-Digest-MD5-2.55-bp153.1.16.x86_64.rpm


Section: User Contributed Perl Documentation (3)
Updated: 2016-03-11


Digest::MD5 - Perl interface to the MD5 Algorithm 


 # 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;


The "Digest::MD5" module allows you to use the RSA Data SecurityInc. MD5 Message Digest algorithm from within Perl programs. Thealgorithm takes as input a message of arbitrary length and produces asoutput 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 hassince 2005 been easy to generate different messages that produce thesame MD5 digest. It still seems hard to generate messages thatproduce a given digest, but it is probably wise to move to strongeralgorithms for applications that depend on the digest to uniquely identifya message.

The "Digest::MD5" module provide a procedural interface for simpleuse, as well as an object oriented interface that can handle messagesof arbitrary length and which can read files directly. 


The following functions are provided by the "Digest::MD5" module.None of these functions are exported by default.
This function will concatenate all arguments, calculate the MD5 digestof this ``message'', and return it in binary form. The returned stringwill be 16 bytes long.

The result of md5(``a'', ``b'', ``c'') will be exactly the same as theresult of md5(``abc'').

Same as md5(), but will return the digest in hexadecimal form. Thelength of the returned string will be 32 and it will only containcharacters from this set: '0'..'9' and 'a'..'f'.
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 containcharacters from this set: 'A'..'Z', 'a'..'z', '0'..'9', '+' and'/'.

Note that the base64 encoded string returned is not padded to be amultiple of 4 bytes long. If you want interoperability with otherbase64 encoded md5 digests you might want to append the redundantstring ``=='' to the result.



The object oriented interface to "Digest::MD5" is described in thissection. After a "Digest::MD5" object has been created, you will adddata to it and finally ask for the digest in a suitable format. Asingle 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 encapsulatethe state of the MD5 message-digest algorithm.

If called as an instance method (i.e. $md5->new) it will just reset thestate the object to the state of a newly created object. No newobject is created in this case.

This is just an alias for $md5->new.
This a copy of the $md5 object. It is useful when you do not want todestroy the digests state, but need an intermediate value of thedigest, e.g. when calculating digests iteratively on a continuous datastream. Example:

    my $md5 = Digest::MD5->new;    while (<>) {        $md5->add($_);        print "Line $.: ", $md5->clone->hexdigest, "\n";    }
The $data provided as argument are appended to the message wecalculate the digest for. The return value is the $md5 object itself.

All these lines will have the same effect on the state of the $md5object:

    $md5->add("a"); $md5->add("b"); $md5->add("c");    $md5->add("a")->add("b")->add("c");    $md5->add("a", "b", "c");    $md5->add("abc");
The $io_handle will be read until EOF and its content appended to themessage we calculate the digest for. The return value is the $md5object itself.

The addfile() method will croak() if it fails reading data for somereason. If it croaks it is unpredictable what the state of the $md5object will be in. The addfile() method might have been able to readthe file partially before it failed. It is probably wise to discardor 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)
Since the MD5 algorithm is byte oriented you might only add bits asmultiples of 8, so you probably want to just use add() instead. Theadd_bits() method is provided for compatibility with other digestimplementations. See Digest for description of the argumentsthat add_bits() take.
Return the binary digest for the message. The returned string will be16 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 anotherdigest value. Call $md5->clone->digest if you want to calculate thedigest without resetting the digest state.

Same as $md5->digest, but will return the digest in hexadecimalform. The length of the returned string will be 32 and it will onlycontain characters from this set: '0'..'9' and 'a'..'f'.
Same as $md5->digest, but will return the digest as a base64 encodedstring. The length of the returned string will be 22 and it will onlycontain characters from this set: 'A'..'Z', 'a'..'z', '0'..'9', '+'and '/'.

The base64 encoded string returned is not padded to be a multiple of 4bytes long. If you want interoperability with other base64 encodedmd5 digests you might want to append the string ``=='' to the result.

@ctx = $md5->context
Saves or restores the internal state. When called with no arguments,returns a 3-element list: number of blocks processed, a 16-byteinternal state buffer, then up to 63 bytes of unprocessed data. Whenpassed those same arguments, restores the state. This is only usefulfor specialised operations.


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 weare 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 ofthe 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 beused on strings that contains chars with ordinal number above 255 (Unicodestrings). The MD5 functions and methods will croak if you try to feed themsuch 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-8representation of such strings. This is achieved by filtering thestring 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




RFC 1321

The paper ``How to Break MD5 and Other Hash Functions'' by Xiaoyun Wangand Hongbo Yu. 


This library is free software; you can redistribute it and/ormodify 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 isderived from the reference C code in RFC 1321 which is covered bythe following copyright statement:

Copyright (C) 1991-2, RSA Data Security, Inc. Created 1991. Allrights reserved.

License to copy and use this software is granted provided that itis identified as the ``RSA Data Security, Inc. MD5 Message-DigestAlgorithm'' in all material mentioning or referencing this softwareor this function.

License is also granted to make and use derivative works providedthat such works are identified as ``derived from the RSA DataSecurity, Inc. MD5 Message-Digest Algorithm'' in all materialmentioning or referencing the derived work.

RSA Data Security, Inc. makes no representations concerning eitherthe merchantability of this software or the suitability of thissoftware 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 thisdocumentation and/or software.

This copyright does not prohibit distribution of any version of Perlcontaining this extension under the terms of the GNU or Artisticlicenses. 


The original "MD5" interface was written by Neil Winton("").

The "Digest::MD5" module is written by Gisle Aas <>.




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