NAME

Crypt::GCM - Galois/Counter Mode (GCM)

SYNOPSIS

  use Crypt::GCM;
  use Crypt::Rijndael;
  
  my $gcm = Crypt::GCM->new(-key => $key, -cipher => 'Crypt::Rijndael');
  my $gcm->set_iv($iv);
  my $gcm->aad('');
  my $cipher_string = $gcm->encrypt($message);
  my $tag = $gcm->tag;

DESCRIPTION

The module implements the Galois/Counter Mode (GCM) for Confidentiality and Authentication. The function of GCM in which the plaintext is encrypted into the ciphertext, and an authentication tag is generated on the AAD and the ciphertext.

`new()`

  my $cipher = Crypt::GCM->new(
      -key    => pack 'H*', '00000000000000000000000000000000',
      -cipher => 'Crypt::Rijndael',
  );

The new() method creates an new Crypt::GCM object. It accepts a list of -argument => value pairs selected from the following list:

  Argument     Description
  --------     -----------
  -key         The encryption/decryption key (required)
  
  -cipher      The cipher algorithm (required)
  
=head2 encrypt()

  my $ciphertext = $cipher->encrypt($plaintext);

`decrypt()`

  my $plaintext = $cipher->decrypt($ciphertext);

`set_iv()`

  $cipher->set_iv($iv);

This allows you to change the initialization vector. allow 16byte string.

`aad()`

  $cipher->aad($text);
  my $text = $cipher->aad();

`tag()`

  $cipher->tag($tag);
  my $tag = $cipher->tag();

EXAMPLE

Encrypt

  use Crypt::GCM;
  use Crypt::Rijndael;
  use strict;
  
  my $cipher = Crypt::GCM->new(
      -key => pack 'H*', '00000000000000000000000000000000',
      -cipher => 'Crypt::Rijndael',
  );
  $cipher->set_iv(pack 'H*', '000000000000000000000000');
  $cipher->aad('');
  my $ciphertext = $cipher->encrypt(pack 'H*', '000000000000000000000000000000');
  my $tag = $cipher->tag;

Decrypt

  use Crypt::GCM;
  use Crypt::Rijndael;
  use strict;
  
  my $cipher = Crypt::GCM->new(
      -key => pack 'H*', '00000000000000000000000000000000',
      -cipher => 'Crypt::Rijndael',
  );
  $cipher->set_iv(pack 'H*', '000000000000000000000000');
  $cipher->aad('');
  $cipher->tag(pack 'H*', 'ab6e47d42cec13bdf53a67b21257bddf');
  my $plaintext = $cipher->decrypt(pack 'H*', '0388dace60b6a392f328c2b971b2fe78');
  if (!defined $plaintext) {
      die 'cannot decrypt on GCM mode. please check your Authentication Tag';
  }

AUTHOR

Hiroyuki OYAMA, <oyama@module.jp>

COPYRIGHT AND LICENSE

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself, either Perl version 5.8.6 or, at your option, any later version of Perl 5 you may have available.

Crypt::GCM - Galois/Counter Mode