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<?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.
* Regardless of the used implementation, it will leak length information.
*
* @param string $knownString The string of known length to compare against
* @param string $userInput The string that the user can control
*
* @return bool true if the two strings are the same, false otherwise
*/
public static function equals($knownString, $userInput)
{
if (function_exists('hash_equals')) {
return hash_equals($knownString, $userInput);
}
// Avoid making unnecessary duplications of secret data
if (!is_string($knownString)) {
$knownString = (string) $knownString;
}
if (!is_string($userInput)) {
$userInput = (string) $userInput;
}
$knownLen = self::safeStrlen($knownString);
$userLen = self::safeStrlen($userInput);
// Set the result to the difference between the lengths
$result = $knownLen - $userLen;
// Always iterate over the minimum length possible.
$iterationLen = min($knownLen, $userLen);
for ($i = 0; $i < $iterationLen; $i++) {
$result |= (ord($knownString[$i]) ^ ord($userInput[$i]));
}
// They are only identical strings if $result is exactly 0...
return 0 === $result;
}
/**
* Return the number of bytes in a string
*
* @param string $string The string whose length we wish to obtain
* @return int
*/
public static function safeStrlen($string)
{
// Premature optimization
// Since this cannot be changed at runtime, we can cache it
static $func_exists = null;
if ($func_exists === null) {
$func_exists = function_exists('mb_strlen');
}
if ($func_exists) {
return mb_strlen($string, '8bit');
}
return strlen($string);
}
}
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