NAME

Crypt::Mode::CTR - Block cipher mode CTR [Counter mode]

SYNOPSIS

   use Crypt::Mode::CTR;
   my $m = Crypt::Mode::CTR->new('AES');
   #(en|de)crypt at once
   my $ciphertext = $m->encrypt($plaintext, $key, $iv);
   my $plaintext = $m->decrypt($ciphertext, $key, $iv);
   #encrypt more chunks
   $m->start_encrypt($key, $iv);
   my $ciphertext = $m->add('some data');
   $ciphertext .= $m->add('more data');
   #decrypt more chunks
   $m->start_decrypt($key, $iv);
   my $plaintext = $m->add($some_ciphertext);
   $plaintext .= $m->add($more_ciphertext);

DESCRIPTION

This module implements CTR cipher mode. NOTE: it works only with ciphers from CryptX (Crypt::Cipher::NNNN).

METHODS

new

 my $m = Crypt::Mode::CTR->new($cipher_name);
 #or
 my $m = Crypt::Mode::CTR->new($cipher_name, $ctr_mode, $ctr_width);
 #or
 my $m = Crypt::Mode::CTR->new($cipher_name, $ctr_mode, $ctr_width, $cipher_rounds);
 # $cipher_name .. one of 'AES', 'Anubis', 'Blowfish', 'CAST5', 'Camellia', 'DES', 'DES_EDE',
 #                 'KASUMI', 'Khazad', 'MULTI2', 'Noekeon', 'RC2', 'RC5', 'RC6',
 #                 'SAFERP', 'SAFER_K128', 'SAFER_K64', 'SAFER_SK128', 'SAFER_SK64',
 #                 'SEED', 'Skipjack', 'Twofish', 'XTEA', 'IDEA', 'Serpent'
 #                 simply any <NAME> for which there exists Crypt::Cipher::<NAME>
 # $ctr_mode ..... 0 little-endian counter (DEFAULT)
 #                 1 big-endian counter
 #                 2 little-endian + RFC3686 incrementing
 #                 3 big-endian + RFC3686 incrementing
 # $ctr_width .... counter width in bytes (DEFAULT = full block width)
 # $cipher_rounds ... optional num of rounds for given cipher

encrypt

   my $ciphertext = $m->encrypt($plaintext, $key, $iv);

decrypt

   my $plaintext = $m->decrypt($ciphertext, $key, $iv);

start_encrypt

   $m->start_encrypt($key, $iv);

start_decrypt

   $m->start_decrypt($key, $iv);

add

   # in encrypt mode
   my $plaintext = $m->add($ciphertext);
   # in decrypt mode
   my $ciphertext = $m->add($plaintext);