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