Make CI_Session's HMAC comparison time-attack-safe
diff --git a/system/libraries/Session/drivers/Session_cookie.php b/system/libraries/Session/drivers/Session_cookie.php
index 971dfea..c8dfad6 100644
--- a/system/libraries/Session/drivers/Session_cookie.php
+++ b/system/libraries/Session/drivers/Session_cookie.php
@@ -395,7 +395,15 @@
$hmac = substr($session, $len);
$session = substr($session, 0, $len);
- if ($hmac !== hash_hmac('sha1', $session, $this->encryption_key))
+ // Time-attack-safe comparison
+ $hmac_check = hash_hmac('sha1', $session, $this->encryption_key);
+ $diff = 0;
+ for ($i = 0; $i < 40; $i++)
+ {
+ $diff |= ord($hmac[$i]) ^ ord($hmac_check[$i]);
+ }
+
+ if ($diff !== 0)
{
log_message('error', 'The session cookie data did not match what was expected.');
$this->sess_destroy();