package Digest;

use strict;
use vars qw($VERSION %MMAP $AUTOLOAD);

$VERSION = "1.14";

%MMAP = (
  "SHA-1"      => ["Digest::SHA1", ["Digest::SHA", 1], ["Digest::SHA2", 1]],
  "SHA-224"    => [["Digest::SHA", 224]],
  "SHA-256"    => [["Digest::SHA", 256], ["Digest::SHA2", 256]],
  "SHA-384"    => [["Digest::SHA", 384], ["Digest::SHA2", 384]],
  "SHA-512"    => [["Digest::SHA", 512], ["Digest::SHA2", 512]],
  "HMAC-MD5"   => "Digest::HMAC_MD5",
  "HMAC-SHA-1" => "Digest::HMAC_SHA1",
  "CRC-16"     => [["Digest::CRC", type => "crc16"]],
  "CRC-32"     => [["Digest::CRC", type => "crc32"]],
  "CRC-CCITT"  => [["Digest::CRC", type => "crcccitt"]],
);

sub new
{
    shift;  # class ignored
    my $algorithm = shift;
    my $impl = $MMAP{$algorithm} || do {
	$algorithm =~ s/\W+//;
	"Digest::$algorithm";
    };
    $impl = [$impl] unless ref($impl);
    my $err;
    for  (@$impl) {
	my $class = $_;
	my @args;
	($class, @args) = @$class if ref($class);
	no strict 'refs';
	unless (exists ${"$class\::"}{"VERSION"}) {
	    eval "require $class";
	    if ($@) {
		$err ||= $@;
		next;
	    }
	}
	return $class->new(@args, @_);
    }
    die $err;
}

sub AUTOLOAD
{
    my $class = shift;
    my $algorithm = substr($AUTOLOAD, rindex($AUTOLOAD, '::')+2);
    $class->new($algorithm, @_);
}

1;

__END__

=head1 NAME

Digest - Modules that calculate message digests

=head1 SYNOPSIS

  $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);

=head1 DESCRIPTION

The C<Digest::> 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
I<likely> to change if the message change in some way.  Another
property is that digest functions are one-way functions, that is it
should be I<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.

Note that the properties of the algorithms change over time, as the
algorithms are analyzed and machines grow faster.  If your application
for instance depends on it being "impossible" to generate the same
digest for a different message it is wise to make it easy to plug in
stronger algorithms as the one used grow weaker.  Using the interface
documented here should make it easy to change algorithms later.

All C<Digest::> 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: