# Prevention of Controller Area Network (CAN) Attacks on Electric Autonomous Vehicles
## 8 Conclusions  
With the increase in connectivity of autonomous vehicles and their reliance on software for functionality, as well as the rise in inner connectivity between a vehicle's ECUs through the CAN bus, the importance of cybersecurity schemes to counter CAN bus attacks has significantly increased. Due to the limitations of current cryptographic encryption and authentication schemes, and intrusion detection systems, this study proposed a secure boot scheme to prevent CAN bus attacks at the ECU level. The proposed secure boot scheme implements a secure boot process in all ECUs that are connected to the CAN bus to detect and mitigate the presence of unauthorized modification of the ECUs' software. This prevents the access of an ECU with an injected malicious code to the CAN bus. The proposed secure boot scheme is capable of detecting and mitigating major and minor malicious code injection attacks to both host cores and the HSM core. Hence, the proposed secure boot scheme is able to prevent all CAN bus attacks that may result from a malicious code.  
This study compared various secure boot strategies, outlining the advantages and disadvantages of each. Additionally, this study analyzed the performance of six data integrity schemes on the secure boot process of the TC399 32-bit AURIX(tm) TriCore(tm) microcontroller. The test results indicate that the recommended data integrity algorithms for secure boot processes of the AURIX TC399 are (1) the AES 128 CMAC algorithm implemented using the HSM AES encryption/decryption device because it is the fastest algorithm with an execution rate of 26.07 (ms/MB), and it provides comparable strength to the HMAC or SHA 256 algorithms; (2) the ECDSA P256 SHA 256, which uses the HSM true number generator, hash module, and PKC module, because it provides higher security level than the CMAC algorithm without a large speed cost, such as the speed cost of the RSASA PSS SHA 256; and (3) the ECDSA P256 AES 128 CMAC, which is a novel approach that utilizes the AES 128 CMAC instead of the SHA 256 in code image generation. This approach combines the strength advantage of the ECDSA algorithm and the speed advantage of the CMAC algorithm, resulting in a 19% performance gain over to the standard hash-based ECDSA.  
The limitations of the proposed secure boot scheme are that it cannot detect the presence of a malicious ECU added to the network. As a result, it cannot mitigate attacks that result from this path. Also, the secure boot scheme has a large cost of implementation because all ECUs connected to the CAN bus must perform a secure boot process for the scheme to be effective.  
The planned future work aims to address the limitations of the secure boot scheme by exploring detection systems that can identify and mitigate malicious ECUs that are connected to the network. Sucha detection system could be integrated with the secure boot scheme to protect vehicles from the two possible attack paths.  
Conceptualization, S.A., A.M. and S.A.M.; methodology, S.A. and A.M.; software, S.A.; validation, S.A.; formal analysis, S.A.; investigation, S.A. and A.M.; writing--original draft preparation, S.A.; writing--review and editing, S.A., A.M., S.A.M. and S.H.; supervision, A.M., S.A.M. and S.H. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
**Institutional Review Board Statement:** Not applicable.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Data Integrity Algorithm** & **Used Hardware** & **Secure boot Execution Rate (ms/MB)** \\ \hline AES 128 CMAC [32] & HSM of AURIX TC27x & 40 \\ AES 128 CMAC [55] & HSM of AURIX & 111.13 \\ AES 128 CMAC (This paper) & TX377 TP & 26.07 \\  & HSM of AURIX TC399 & 275.71 \\ SHA 256 [55] & TC377 TP & 275.71 \\ SHA 256 (this paper) & HSM of AURIX TC399 & 52.27 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Comparing the implementations of the AES CMAC algorithms and SHA 256 algorithms.