Efficient Physical Layer Key Agreement for FlexRay Networks

The FlexRay protocol provides deterministic and fault-tolerant communication for automotive applications with stringent requirements regarding reliability and real-time performance. But the lack of intrinsic security mechanisms makes FlexRay vulnerable to spoofing and DoS attacks while existing features are not sufficient to assure reliable communication in the presence of adversaries. Since adding cryptography mandates for secret shared keys, providing secure key establishment techniques is critical in assuring the intended security objectives. In this paper we propose a backward compatible key agreement scheme for FlexRay communication based on intrinsic characteristics of the FlexRay physical layer. In particular, we determine that the symbol window is suitable for implementing a covert channel based on physical properties of the bus which allows us to bootstrap a secure session key between two nodes or to re-enforce existing shared keys. We evaluate and discuss the performance of software-based implementations of the proposed mechanism on two different automotive embedded platforms relying only on the application level.