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 <terrafrost@php.net>
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
16namespace phpseclib3\Math\BigInteger\Engines;
17
18use phpseclib3\Crypt\RSA\Formats\Keys\PKCS8;
19use phpseclib3\Math\BigInteger;
20
21/**
22 * OpenSSL Modular Exponentiation Engine
23 *
24 * @package Engines
25 * @author  Jim Wigginton <terrafrost@php.net>
26 * @access  public
27 */
28abstract 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}
73