US Patent 9331854 Message authentication method in communication system and communication system

Each of ECUs counts the number of messages transmitted for each of CAN IDs. A transmission node that has transmitted a main message produces an MAC from a data field and the CAN ID in the main message and a counter value corresponding to the CAN ID, and transmits the MAC as an MAC message. A reception node that has received the main message produces an MAC from the data field and the CAN ID contained in the main message and the counter value corresponding to the CAN ID, and determines whether the MAC matches the MAC contained in the MAC message. By so doing, verification whether the main message is valid or not can be made. According to this configuration, message authentication by the MAC can be made without changing a CAN protocol.