Merge pull request #17 from firebase/constant-time

Constant time string comparison function in verify method

2 files changed, 19 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);
         }
     }
 
diff --git a/tests/JWTTest.php b/tests/JWTTest.php
index ee131d4..2149862 100644
--- a/tests/JWTTest.php
+++ b/tests/JWTTest.php
@@ -47,6 +47,15 @@ class JWTTest extends PHPUnit_Framework_TestCase {
 		$this->assertEquals($decoded->message, 'abc');
 	}
 
+	function testInvalidToken() {
+		$payload = array(
+			"message" => "abc",
+			"exp" => time() + 20); // time in the future
+		$encoded = JWT::encode($payload, 'my_key');
+		$this->setExpectedException('UnexpectedValueException');
+		$decoded = JWT::decode($encoded, 'my_key2');
+	}
+
 	function testRSEncodeDecode() {
 		$privKey = openssl_pkey_new(array('digest_alg' => 'sha256',
 			'private_key_bits' => 1024,