Add test case verifying no t= (timestamp) with x= (expiration) in signature

dkim/tests/test_dkim.py

@@ -62,6 +62,7 @@ class TestSignAndVerify(unittest.TestCase):
         self.message5 = read_test_data("rfc6376.signed.rsa.msg")
         self.message6 = read_test_data("test.message.baddomain")
         self.message7 = read_test_data("rfc6376.w1258.msg")
+        self.message8 = read_test_data("rfc6376.signed.no_t.msg")
         self.key = read_test_data("test.private")
         self.rfckey = read_test_data("rfc8032_7_1.key")
 
@@ -250,6 +251,7 @@ b/mPfjC0QJTocVBq6Za/PlzfV+Py92VaCak19F4WrbVTK5Gg5tW220MCAwEAAQ=="""
                 d = dkim.DKIM(self.message4)
                 res = d.verify(dnsfunc=self.dnsfunc5)
                 self.assertTrue(res)
+
     def test_non_utf8(self):
         # A message with Windows-1258 encoding is signed and verifies.
         for header_algo in (b"simple", b"relaxed"):
@@ -262,6 +264,13 @@ b/mPfjC0QJTocVBq6Za/PlzfV+Py92VaCak19F4WrbVTK5Gg5tW220MCAwEAAQ=="""
                 # As of 1.1.0 this won't verify, but at least we don't crash.  FIXME
                 self.assertFalse(res)
 
+    def test_no_t(self):
+        # Signature Timestamp is optional, so don't crash if it's missing.
+        d = dkim.DKIM(self.message8)
+        res = d.verify(dnsfunc=self.dnsfunc5)
+        # Signature won't verify, but that's not what we are testing.
+        self.assertFalse(res)
+
     def test_catch_bad_key(self):
         # Raise correct error for defective public key.
         d = dkim.DKIM(self.message5)