Switching to a constant-time string comparison in the verify method

1 files changed, 10 insertions, 1 deletions

diff --git a/Authentication/JWT.php b/Authentication/JWT.php
index 38a4f7e..90c1ac7 100644
--- a/Authentication/JWT.php
+++ b/Authentication/JWT.php
@@ -157,7 +157,16 @@ class JWT
                 }
             case 'hash_hmac':
             default:
-                return $signature === hash_hmac($algo, $msg, $key, true);
+                $hash = hash_hmac($algo, $msg, $key, true);
+                $len = min(strlen($signature), strlen($hash));
+
+                $status = 0;
+                for ($i = 0; $i < $len; $i++) {
+                    $status |= (ord($signature[$i]) ^ ord($hash[$i]));
+                }
+                $status |= (strlen($signature) ^ strlen($hash));
+
+                return ($status === 0);
         }
     }