The Controller Area Network (CAN) is a widely used industry-standard intra-vehicle broadcast network that connects the Electronic Control Units (ECUs) which control most car systems. The CAN contains substantial vulnerabilities that can be exploited by attackers to gain control of the vehicle, due to its lack of security measures. To prevent an attacker from sending malicious messages through the CAN bus to take over a vehicle, we propose the addition of a secure hardware-based module, or Security ECU (SECU), onto the CAN bus. The SECU can perform key distribution and message verification, as well as corrupting malicious messages before they are fully received by an ECU. Only software modification is needed for existing ECUs, without changing the CAN protocol. This provides backward compatibility with existing CAN systems. Furthermore, we collect 6.673 million CAN bus messages from various cars, and find that the CAN messages collectively have low entropy, with an average of 11.915 bits. This finding motivates our proposal for CAN bus message compression, which allows us to significantly reduce message size to fit the message and its message authentication code (MAC) within one CAN frame, enabling fast authentication. Since ECUs only need to generate the MACs (and not verify them), the delay and computation overhead are also reduced compared to traditional authentication mechanisms. Our authentication mechanism is implemented on a realistic testbed using industry standard MCP2551 CAN transceivers and Raspberry Pi embedded systems. Experimental results demonstrate that our mechanism can achieve real-time message authentication on the CAN bus with minimal latency.
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