<?php
/*
* This file is part of the Symfony package.
*
* (c) Fabien Potencier <fabien@symfony.com>
*
* For the full copyright and license information, please view the LICENSE
* file that was distributed with this source code.
*/
namespace Symfony\Component\Security\Core\Util;
/**
* String utility functions.
*
* @author Fabien Potencier <fabien@symfony.com>
*/
class StringUtils
{
/**
* This class should not be instantiated
*/
private function __construct() {}
/**
* Compares two strings.
*
* This method implements a constant-time algorithm to compare strings.
*
* @param string $knownString The string of known length to compare against
* @param string $userInput The string that the user can control
*
* @return Boolean true if the two strings are the same, false otherwise
*/
public static function equals($knownString, $userInput)
{
// Prevent issues if string length is 0
$knownString .= chr(0);
$userInput .= chr(0);
$knownLen = strlen($knownString);
$userLen = strlen($userInput);
// Set the result to the difference between the lengths
$result = $knownLen - $userLen;
// Note that we ALWAYS iterate over the user-supplied length
// This is to prevent leaking length information
for ($i = 0; $i < $userLen; $i++) {
// Using % here is a trick to prevent notices
// It's safe, since if the lengths are different
// $result is already non-0
$result |= (ord($knownString[$i % $knownLen]) ^ ord($userInput[$i]));
}
// They are only identical strings if $result is exactly 0...
return 0 === $result;
}
}
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