unify exceptions between raw and compressed encoding

make the decoding of malformed point raise the same exception irrespective
of the formatting of the key/public point

Author: tomato42

src/ecdsa/keys.py

@@ -55,8 +55,9 @@ def _from_raw_encoding(string, curve, validate_point):
         assert len(ys) == curve.baselen, (len(ys), curve.baselen)
         x = string_to_number(xs)
         y = string_to_number(ys)
-        if validate_point:
-            assert ecdsa.point_is_valid(curve.generator, x, y)
+        if validate_point and not ecdsa.point_is_valid(curve.generator, x, y):
+            raise MalformedPoint("Point does not lie on the curve")
+
         return ellipticcurve.Point(curve.curve, x, y, order)
 
     @staticmethod

src/ecdsa/test_pyecdsa.py

@@ -416,6 +416,14 @@ def test_decoding_with_malformed_compressed(self):
         with self.assertRaises(MalformedPoint):
             VerifyingKey.from_string(b('\x01') + enc[:24])
 
+    def test_decoding_with_point_not_on_curve(self):
+        enc = b('\x0c\xe0\x1d\xe0d\x1c\x8eS\x8a\xc0\x9eK\xa8x !\xd5\xc2\xc3'
+                '\xfd\xc8\xa0c\xff\xfb\x02\xb9\xc4\x84)\x1a\x0f\x8b\x87\xa4'
+                'z\x8a#\xb5\x97\xecO\xb6\xa0HQ\x89*')
+
+        with self.assertRaises(MalformedPoint):
+            VerifyingKey.from_string(enc[:47] + b('\x00'))
+
     def test_decoding_with_point_at_infinity(self):
         # decoding it is unsupported, as it's not necessary to encode it
         with self.assertRaises(MalformedPoint):