Raise ValueError from verify_digest for Edwards curve keys (fixes #349)

src/ecdsa/keys.py

@@ -718,10 +718,15 @@ def verify_digest(
         :raises BadSignatureError: if the signature is invalid or malformed
         :raises BadDigestError: if the provided digest is too big for the curve
             associated with this VerifyingKey and allow_truncate was not set
+        :raises ValueError: if this is an Edwards curve key; use
+            :func:`~VerifyingKey.verify` instead, as EdDSA signs the message
+            directly and does not operate on pre-hashed digests
 
         :return: True if the verification was successful
         :rtype: bool
         """
+        if isinstance(self.curve.curve, CurveEdTw):
+            raise ValueError("Method unsupported for Edwards curves")
         # signature doesn't have to be a bytes-like-object so don't normalise
         # it, the decoders will do that
         digest = normalise_bytes(digest)

src/ecdsa/test_keys.py

@@ -438,6 +438,20 @@ def test_ed25519_sig_verify_malformed(self):
         with self.assertRaises(BadSignatureError):
             vk.verify(sig, data)
 
+    def test_ed25519_verify_digest(self):
+        vk_pem = (
+            "-----BEGIN PUBLIC KEY-----\n"
+            "MCowBQYDK2VwAyEAIwBQ0NZkIiiO41WJfm5BV42u3kQm7lYnvIXmCy8qy2U=\n"
+            "-----END PUBLIC KEY-----\n"
+        )
+
+        vk = VerifyingKey.from_pem(vk_pem)
+
+        with self.assertRaises(ValueError) as e:
+            vk.verify_digest(b"a" * 64, b"b" * 32)
+
+        self.assertIn("Method unsupported for Edwards", str(e.exception))
+
     def test_ed448_from_pem(self):
         pem_str = (
             "-----BEGIN PUBLIC KEY-----\n"