<?php
/**
 * @see       https://github.com/zendframework/zend-crypt for the canonical source repository
 * @copyright Copyright (c) 2005-2018 Zend Technologies USA Inc. (https://www.zend.com)
 * @license   https://github.com/zendframework/zend-crypt/blob/master/LICENSE.md New BSD License
 */

namespace Zend\Crypt;

use function function_exists;
use function hash_equals;
use function mb_strlen;
use function min;
use function ord;

/**
 * Tools for cryptography
 */
class Utils
{
    /**
     * Compare two strings to avoid timing attacks
     *
     * C function memcmp() internally used by PHP, exits as soon as a difference
     * is found in the two buffers. That makes possible of leaking
     * timing information useful to an attacker attempting to iteratively guess
     * the unknown string (e.g. password).
     * The length will leak.
     *
     * @param  string $expected
     * @param  string $actual
     * @return bool
     */
    public static function compareStrings($expected, $actual)
    {
        $expected     = (string) $expected;
        $actual       = (string) $actual;

        if (function_exists('hash_equals')) {
            return hash_equals($expected, $actual);
        }

        $lenExpected  = mb_strlen($expected, '8bit');
        $lenActual    = mb_strlen($actual, '8bit');
        $len          = min($lenExpected, $lenActual);

        $result = 0;
        for ($i = 0; $i < $len; $i++) {
            $result |= ord($expected[$i]) ^ ord($actual[$i]);
        }
        $result |= $lenExpected ^ $lenActual;

        return ($result === 0);
    }
}
