Fix EIP-155 V reconstruction for ecrecover in client

client/src/ledger_app_clients/ethereum/utils.py

@@ -24,15 +24,31 @@ def recover_transaction(tx_params, vrs: tuple) -> bytes:
         prefix = raw_tx[:1]
         raw_tx = raw_tx[len(prefix):]
     else:
-        # v is returned on one byte only so it might have overflowed
-        # in that case, we will reconstruct it to its full value
         if "chainId" in tx_params:
+            # v is returned on one byte only so it might have overflowed
+            # in that case, we will reconstruct it to its full value
             trunc_chain_id = tx_params["chainId"]
             while trunc_chain_id.bit_length() > 32:
                 trunc_chain_id >>= 8
+
             trunc_target = trunc_chain_id * 2 + 35
-            parity = int.from_bytes(vrs[0], "big") - (trunc_target & 0xff)
-            vrs = (parity + tx_params["chainId"] * 2 + 35, vrs[1], vrs[2])
+            trunc_v = int.from_bytes(vrs[0], "big")
+
+            if (trunc_target & 0xff) == trunc_v:
+                parity = 0
+            elif ((trunc_target + 1) & 0xff) == trunc_v:
+                parity = 1
+            else:
+                # should have matched with a previous if
+                assert False
+
+            # https://github.com/ethereum/EIPs/blob/master/EIPS/eip-155.md
+            full_v = parity + tx_params["chainId"] * 2 + 35
+            # 9 bytes would be big enough even for the biggest chain ID
+            vrs = (int(full_v).to_bytes(9, "big"), vrs[1], vrs[2])
+        else:
+            # Pre EIP-155 TX
+            assert False
     decoded = rlp.decode(raw_tx)
     reencoded = rlp.encode(decoded[:-3] + list(vrs))
     addr = Account.recover_transaction(prefix + reencoded)