1<?php
2/**
3 * Copyright 2017 Facebook, Inc.
4 *
5 * You are hereby granted a non-exclusive, worldwide, royalty-free license to
6 * use, copy, modify, and distribute this software in source code or binary
7 * form for use in connection with the web services and APIs provided by
8 * Facebook.
9 *
10 * As with any software that integrates with the Facebook platform, your use
11 * of this software is subject to the Facebook Developer Principles and
12 * Policies [http://developers.facebook.com/policy/]. This copyright notice
13 * shall be included in all copies or substantial portions of the software.
14 *
15 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
16 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
17 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
18 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
19 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
20 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
21 * DEALINGS IN THE SOFTWARE.
22 *
23 */
24
25/**
26 * @see https://github.com/sarciszewski/php-future/blob/master/src/Security.php#L37-L51
27 */
28if (!function_exists('hash_equals')) {
29    function hash_equals($knownString, $userString)
30    {
31        if (function_exists('mb_strlen')) {
32            $kLen = mb_strlen($knownString, '8bit');
33            $uLen = mb_strlen($userString, '8bit');
34        } else {
35            $kLen = strlen($knownString);
36            $uLen = strlen($userString);
37        }
38        if ($kLen !== $uLen) {
39            return false;
40        }
41        $result = 0;
42        for ($i = 0; $i < $kLen; $i++) {
43            $result |= (ord($knownString[$i]) ^ ord($userString[$i]));
44        }
45
46        // They are only identical strings if $result is exactly 0...
47        return 0 === $result;
48    }
49}
50