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   1  <?php
   2  
   3  /**
   4   * OpenSSL Modular Exponentiation Engine
   5   *
   6   * PHP version 5 and 7
   7   *
   8   * @category  Math
   9   * @package   BigInteger
  10   * @author    Jim Wigginton <[email protected]>
  11   * @copyright 2017 Jim Wigginton
  12   * @license   http://www.opensource.org/licenses/mit-license.html  MIT License
  13   * @link      http://pear.php.net/package/Math_BigInteger
  14   */
  15  
  16  namespace phpseclib3\Math\BigInteger\Engines;
  17  
  18  use phpseclib3\Crypt\RSA\Formats\Keys\PKCS8;
  19  use phpseclib3\Math\BigInteger;
  20  
  21  /**
  22   * OpenSSL Modular Exponentiation Engine
  23   *
  24   * @package Engines
  25   * @author  Jim Wigginton <[email protected]>
  26   * @access  public
  27   */
  28  abstract class OpenSSL
  29  {
  30      /**
  31       * Test for engine validity
  32       *
  33       * @return bool
  34       */
  35      public static function isValidEngine()
  36      {
  37          return extension_loaded('openssl') && static::class != __CLASS__;
  38      }
  39  
  40      /**
  41       * Performs modular exponentiation.
  42       *
  43       * @param Engine $x
  44       * @param Engine $e
  45       * @param Engine $n
  46       * @return Engine
  47       */
  48      public static function powModHelper(Engine $x, Engine $e, Engine $n)
  49      {
  50          if ($n->getLengthInBytes() < 31 || $n->getLengthInBytes() > 16384) {
  51              throw new \OutOfRangeException('Only modulo between 31 and 16384 bits are accepted');
  52          }
  53  
  54          $key = PKCS8::savePublicKey(
  55              new BigInteger($n),
  56              new BigInteger($e)
  57          );
  58  
  59          $plaintext = str_pad($x->toBytes(), $n->getLengthInBytes(), "\0", STR_PAD_LEFT);
  60  
  61          // this is easily prone to failure. if the modulo is a multiple of 2 or 3 or whatever it
  62          // won't work and you'll get a "failure: error:0906D06C:PEM routines:PEM_read_bio:no start line"
  63          // error. i suppose, for even numbers, we could do what PHP\Montgomery.php does, but then what
  64          // about odd numbers divisible by 3, by 5, etc?
  65          if (!openssl_public_encrypt($plaintext, $result, $key, OPENSSL_NO_PADDING)) {
  66              throw new \UnexpectedValueException(openssl_error_string());
  67          }
  68  
  69          $class = get_class($x);
  70          return new $class($result, 256);
  71      }
  72  }