Digest - Modules that calculate message digests

  $md5  = Digest->new("MD5");
  $sha1 = Digest->new("SHA-1");
  $sha256 = Digest->new("SHA-256");
  $sha384 = Digest->new("SHA-384");
  $sha512 = Digest->new("SHA-512");

  $hmac = Digest->HMAC_MD5($key);

The CWDigest:: modules calculate digests, also called fingerprints or hashes, of some data, called a message. The digest is (usually) some small/fixed size string. The actual size of the digest depend of the algorithm used. The message is simply a sequence of arbitrary bytes or bits.

An important property of the digest algorithms is that the digest is likely to change if the message change in some way. Another property is that digest functions are one-way functions, i.e. it should be hard to find a message that correspond to some given digest. Algorithms differ in how likely and how hard, as well as how efficient they are to compute.

All CWDigest:: modules provide the same programming interface. A functional interface for simple use, as well as an object oriented interface that can handle messages of arbitrary length and which can read files directly.

The digest can be delivered in three formats:

binary

This is the most compact form, but it is not well suited for printing or embedding in places that can't handle arbitrary data.

hex

A twice as long string of lowercase hexadecimal digits.

base64

A string of portable printable characters. This is the base64 encoded representation of the digest with any trailing padding removed. The string will be about 30% longer than the binary version. MIME::Base64 tells you more about this encoding.

The functional interface is simply importable functions with the same name as the algorithm. The functions take the message as argument and return the digest. Example:

  use Digest::MD5 qw(md5);
  $digest = md5($message);

There are also versions of the functions with _hex or _base64 appended to the name, which returns the digest in the indicated form.

The following methods are available for all CWDigest:: modules:

$ctx = Digest->XXX($arg,...)

$ctx = Digest::XXX->new($arg,...)

The constructor returns some object that encapsulate the state of the message-digest algorithm. You can add data to the object and finally ask for the digest. The XXX should of course be replaced by the proper name of the digest algorithm you want to use. The two first forms are simply syntactic sugar which automatically load the right module on first use. The second form allow you to use algorithm names which contains letters which are not legal perl identifiers, e.g. SHA-1. If no implementation for the given algorithm can be found, then an exception is raised. If new() is called as an instance method (i.e. CW$ctx->new) it will just reset the state the object to the state of a newly created object. No new object is created in this case, and the return value is the reference to the object (i.e. CW$ctx). The clone method creates a copy of the digest state object and returns a reference to the copy.

$ctx->reset

This is just an alias for CW$ctx->new. The CW$data provided as argument are appended to the message we calculate the digest for. The return value is the CW$ctx object itself. The CW$io_handle is read until EOF and the content is appended to the message we calculate the digest for. The return value is the CW$ctx object itself. The bits provided are appended to the message we calculate the digest for. The return value is the CW$ctx object itself. The two argument form of add_bits() will add the first CW$nbits bits from data. For the last potentially partial byte only the high order CW$nbits % 8 bits are used. If CW$nbits is greater than CWlength($data) * 8, then this method would do the same as CW$ctx->add($data), i.e. CW$nbits is silently ignored. The one argument form of add_bits() takes a CW$bitstring of 1 and 0 chars as argument. It's a shorthand for CW$ctx->add_bits(pack("B*", $bitstring), length($bitstring)). This example shows two calls that should have the same effect:

   $ctx->add_bits("111100001010");
   $ctx->add_bits("\xF0\xA0", 12);

Most digest algorithms are byte based. For those it is not possible to add bits that are not a multiple of 8, and the add_bits() method will croak if you try.

$ctx->digest

Return the binary digest for the message. Note that the CWdigest operation is effectively a destructive, read-once operation. Once it has been performed, the CW$ctx object is automatically CWreset and can be used to calculate another digest value. Call CW$ctx->clone->digest if you want to calculate the digest without reseting the digest state.

$ctx->hexdigest

Same as CW$ctx->digest, but will return the digest in hexadecimal form.

$ctx->b64digest

Same as CW$ctx->digest, but will return the digest as a base64 encoded string.

This table should give some indication on the relative speed of different algorithms. It is sorted by throughput based on a benchmark done with of some implementations of this API:

 Algorithm      Size    Implementation                  MB/s

 MD4            128     Digest::MD4 v1.3               165.0
 MD5            128     Digest::MD5 v2.33               98.8
 SHA-256        256     Digest::SHA2 v1.1.0             66.7
 SHA-1          160     Digest::SHA v4.3.1              58.9
 SHA-1          160     Digest::SHA1 v2.10              48.8
 SHA-256        256     Digest::SHA v4.3.1              41.3
 Haval-256      256     Digest::Haval256 v1.0.4         39.8
 SHA-384        384     Digest::SHA2 v1.1.0             19.6
 SHA-512        512     Digest::SHA2 v1.1.0             19.3
 SHA-384        384     Digest::SHA v4.3.1              19.2
 SHA-512        512     Digest::SHA v4.3.1              19.2
 Whirlpool      512     Digest::Whirlpool v1.0.2        13.0
 MD2            128     Digest::MD2 v2.03                9.5

 Adler-32        32     Digest::Adler32 v0.03            1.3
 CRC-16          16     Digest::CRC v0.05                1.1
 CRC-32          32     Digest::CRC v0.05                1.1
 MD5            128     Digest::Perl::MD5 v1.5           1.0
 CRC-CCITT       16     Digest::CRC v0.05                0.8

These numbers was achieved Apr 2004 with ActivePerl-5.8.3 running under Linux on a P4 2.8 GHz CPU. The last 5 entries differ by being pure perl implementations of the algorithms, which explains why they are so slow.

Digest::Adler32, Digest::CRC, Digest::Haval256, Digest::HMAC, Digest::MD2, Digest::MD4, Digest::MD5, Digest::SHA, Digest::SHA1, Digest::SHA2, Digest::Whirlpool

New digest implementations should consider subclassing from Digest::base.

MIME::Base64

Gisle Aas <gisle@aas.no>

The CWDigest:: interface is based on the interface originally developed by Neil Winton for his CWMD5 module.

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

    Copyright 1998-2001,2003-2004 Gisle Aas.
    Copyright 1995-1996 Neil Winton.