CryptLib/Cipher/Block/Mode/CTR.php

   1 <?php
   2 /**
   3  * The CTR (Counter) mode implementation
   4  *
   5  * PHP version 5.3
   6  *
   7  * @category   PHPCryptLib
   8  * @package    Cipher
   9  * @subpackage Block
  10  * @author     Anthony Ferrara <ircmaxell@ircmaxell.com>
  11  * @copyright  2011 The Authors
  12  * @license    http://www.opensource.org/licenses/mit-license.html  MIT License
  13  * @version    Build @@version@@
  14  */
  15
  16 namespace CryptLib\Cipher\Block\Mode;
  17
  18 use CryptLib\Core\BaseConverter;
  19 use CryptLib\Core\BigMath;
  20
  21 /**
  22  * The CTR (Counter) mode implementation
  23  *
  24  * @category   PHPCryptLib
  25  * @package    Cipher
  26  * @subpackage Block
  27  * @author     Anthony Ferrara <ircmaxell@ircmaxell.com>
  28  */
  29
  30 class CTR extends \CryptLib\Cipher\Block\AbstractMode {
  31
  32     /**
  33      * @var BigMath An instance of the BigMath library
  34      */
  35     protected $bigMath = null;
  36
  37     /**
  38      * Build the instance of the cipher mode
  39      *
  40      * @param Cipher $cipher  The cipher to use for encryption/decryption
  41      * @param string $initv   The initialization vector (empty if not needed)
  42      * @param array  $options An array of mode-specific options
  43      */
  44     public function __construct(
  45         \CryptLib\Cipher\Block\Cipher $cipher,
  46         $initv,
  47         array $options = array()
  48     ) {
  49         parent::__construct($cipher, $initv, $options);
  50         $this->bigMath = BigMath::createFromServerConfiguration();
  51     }
  52
  53     /**
  54      * Reset the mode to start over (destroying any intermediate state)
  55      *
  56      * @return void
  57      */
  58     public function reset() {
  59         $this->state = BaseConverter::ConvertFromBinary($this->initv, '0123456789');
  60         $this->state = ltrim($this->state, '0');
  61     }
  62
  63     /**
  64      * Decrypt the data using the supplied key, cipher
  65      *
  66      * @param string $data The data to decrypt
  67      *
  68      * @return string The decrypted data
  69      */
  70     protected function decryptBlock($data) {
  71         return $this->encryptBlock($data);
  72     }
  73
  74     /**
  75      * Encrypt the data using the supplied key, cipher
  76      *
  77      * @param string $data The data to encrypt
  78      *
  79      * @return string The encrypted data
  80      */
  81     protected function encryptBlock($data) {
  82         $size        = $this->cipher->getBlockSize();
  83         $state       = str_pad(
  84             BaseConverter::convertToBinary($this->state, '0123456789'),
  85             $size,
  86             chr(0),
  87             STR_PAD_LEFT
  88         );
  89         $stub        = $this->cipher->encryptBlock($state);
  90         $this->state = $this->bigMath->add($this->state, 1);
  91         return $stub ^ $data;
  92     }
  93
  94 }