minor #11574 [Security] Made optimization on constant-time algorithm removing modulus operator (yosmanyga)
This PR was merged into the 2.3 branch.
Discussion
----------
[Security] Made optimization on constant-time algorithm removing modulus operator
| Q | A
| ------------- | ---
| Bug fix? | no
| New feature? | no
| BC breaks? | no
| Deprecations? | no
| Tests pass? | yes
| Fixed tickets | -
| License | MIT
| Doc PR | -
This fix improves the constant-time algorithm used to compare strings, as it removes the `%` operator inside the loop.
Commits
-------
000bd0d
Made optimization deprecating modulus operator
This commit is contained in:
commit
b5d0501860
@ -35,23 +35,19 @@ class StringUtils
|
||||
*/
|
||||
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);
|
||||
|
||||
// Extend know string to avoid uninitialized string offsets
|
||||
$knownString .= $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]));
|
||||
$result |= (ord($knownString[$i]) ^ ord($userInput[$i]));
|
||||
}
|
||||
|
||||
// They are only identical strings if $result is exactly 0...
|
||||
|
Reference in New Issue
Block a user