eth/verify: path is not validated; improve invalid signature handling

Ethereum's verify_function takes an actual address as an argument not a
derivation path. So any path validation does not make any sense.

Also, if the verify_recover function raises an exception, it gets
propogated as a DataError (additional fix for #422).

Author: tsusanka

src/apps/ethereum/verify_message.py

@@ -6,21 +6,22 @@
 from trezor.messages.Success import Success
 from trezor.ui.text import Text
 
-from .address import validate_full_path
-
-from apps.common import paths
 from apps.common.confirm import require_confirm
 from apps.common.layout import split_address
 from apps.common.signverify import split_message
 from apps.ethereum.sign_message import message_digest
 
 
 async def verify_message(ctx, msg):
-    await paths.validate_path(ctx, validate_full_path, path=msg.address)
-
     digest = message_digest(msg.message)
+    if len(msg.signature) != 65:
+        raise wire.DataError("Invalid signature")
     sig = bytearray([msg.signature[64]]) + msg.signature[:64]
-    pubkey = secp256k1.verify_recover(sig, digest)
+
+    try:
+        pubkey = secp256k1.verify_recover(sig, digest)
+    except ValueError:
+        raise wire.DataError("Invalid signature")
 
     if not pubkey:
         raise wire.DataError("Invalid signature")