Symmetric key distribution for car-to-car/infrastructure communication systems

Services such as sending a pre-crash sensing warning and traffic condition warning are expected to be provided in car-to-car/infrastructure (C2X) communication systems. Maintaining message integrity is essential for these services because wrong messages may cause collision accidents and congestion. A message authentication code (MAC) generated by using a symmetric key is used to authenticate a message. The sender and receiver of a message must possess the same symmetric key before initiating communications. In the mentioned warning services, the sender of a message cannot know who receives the message, because the message is broadcast. Moreover, it is difficult for a road-side unit (RSU) to distribute a key to an onboard unit (OBU) because an OBU cannot always communicate with a RSU. Therefore, key distribution is a problem in C2X communication systems. We thus propose a protocol for key distribution. In the protocol, all OBUs and RSUs that exist in a certain area possess the same key. An OBU obtains the keys for the area in which the OBU is present and for the area to which the OBU will go next. The protocol enables a vehicle to verify message integrity by using a symmetric key in C2X communication systems.