Merge pull request #283 from tlsfuzzer/fix-py3.3-compat

workaround py3.3 bug with empty strings and memoryview

src/ecdsa/_compat.py

@@ -100,18 +100,24 @@ def hmac_compat(data):
                 return bytes(data)
             return data
 
+        def normalise_bytes(buffer_object):
+            """Cast the input into array of bytes."""
+            if not buffer_object:
+                return b""
+            return memoryview(buffer_object).cast("B")
+
     else:
 
         def hmac_compat(data):
             return data
 
+        def normalise_bytes(buffer_object):
+            """Cast the input into array of bytes."""
+            return memoryview(buffer_object).cast("B")
+
     def compat26_str(val):
         return val
 
-    def normalise_bytes(buffer_object):
-        """Cast the input into array of bytes."""
-        return memoryview(buffer_object).cast("B")
-
     def remove_whitespace(text):
         """Removes all whitespace from passed in string"""
         return re.sub(r"\s+", "", text, flags=re.UNICODE)

src/ecdsa/test_keys.py

@@ -550,6 +550,15 @@ def test_equality_on_signing_keys(self):
         self.assertEqual(self.sk1, sk)
         self.assertEqual(self.sk1_pkcs8, sk)
 
+    def test_verify_with_empty_message(self):
+        sig = self.sk1.sign(b"")
+
+        self.assertTrue(sig)
+
+        vk = self.sk1.verifying_key
+
+        self.assertTrue(vk.verify(sig, b""))
+
     def test_verify_with_precompute(self):
         sig = self.sk1.sign(b"message")