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[Security] Use hash_equals for constant-time string comparison (again) #11822

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Merged
merged 2 commits into from
Sep 10, 2014
Merged

[Security] Use hash_equals for constant-time string comparison (again) #11822

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03bd74b
[Security] Use hash_equals for constant-time string comparison
dunglas Sep 1, 2014
3071557
[Security] Add more tests for StringUtils::equals
dunglas Aug 31, 2014
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[Security] Use hash_equals for constant-time string comparison
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@dunglas
dunglas committed Sep 4, 2014
commit 03bd74bdeae5e686cb15e6ec2b3b629f58211419
10 changes: 9 additions & 1 deletion src/Symfony/Component/Security/Core/Util/StringUtils.php
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Original file line number Diff line number Diff line change
Expand Up @@ -27,6 +27,7 @@ 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 $userInput The string that the user can control
Expand All @@ -35,6 +36,13 @@ private function __construct() {}
*/
public static function equals($knownString, $userInput)
{
$knownString = (string) $knownString;
$userInput = (string) $userInput;

if (function_exists('hash_equals')) {
return hash_equals($knownString, $userInput);
}

$knownLen = strlen($knownString);
$userLen = strlen($userInput);

Expand All @@ -45,7 +53,7 @@ public static function equals($knownString, $userInput)
$result = $knownLen - $userLen;

// Note that we ALWAYS iterate over the user-supplied length
// This is to prevent leaking length information
// This is to mitigate leaking length information
for ($i = 0; $i < $userLen; $i++) {
$result |= (ord($knownString[$i]) ^ ord($userInput[$i]));
}
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