BusCount: A Provable Replay Protection Solution for Automotive CAN Networks
Information technology has become eminent in the development of modern cars. More than 50 Electronic Control Units (ECUs) realize vehicular functions in hardware and software, ranging from engine control and infotainment to future autonomous driving systems. Not only do the connections to the outside world pose new threats, but also the in-vehicle communication between ECUs, realized by bus systems such as Controller Area Network (CAN), needs to be protected against manipulation and replay of messages. Multiple countermeasures were presented in the past making use of Message Authentication Codes and time stamps and message counters, respectively, to provide message freshness, most prominently AUTOSAR's Secure Onboard Communication (SecOC). In this paper, we focus on the latter ones. As one aspect of this paper, using an adequate formal model and proof, we will show that the currently considered solutions exhibit deficiencies that are hard if not impossible to overcome within the scope of the respective approaches. We further present a hardware-based approach that avoids these deficiencies and formally prove its freshness properties. In addition, we show its practicability by a hardware implementation. Finally, we evaluate our approach in comparison to counter-based solutions currently being used.