## 4 Security Issues and Solutions for CAVs
### Cyber-Attacks on Inter-Vehicle Systems
#### 4.2.3 Open Issues of Inter-Vehicle System Security  
Although the diverse types of cyber-attacks on a platoon and the corresponding solutions have been well studied, some open issues to be considered still exist. Presently, the platooning probability on the road is low. Most existing work either assumes an individual driving pattern or considers cooperative driving (e.g., platoon) only in the design of inter-vehicle message dissemination. Furthermore, in most cases, several \begin{table}
\begin{tabular}{l l l} \hline \hline \multicolumn{1}{c}{**Cyber Physical Attacks**} & \multicolumn{2}{c}{**Workable Solutions**} \\ \hline Message tampering & (1) & Data correction. \\  & (2) & Challenge response authentication. \\ \hline  & (1) & Use vehicular PKI for authentication. \\  & (2) & Sign warning message. \\ Forgery attacks & (3) & Establish group communication. \\  & (4) & Use non-cryptography checksum and plausibility check per message. \\ \hline Message saturation & (1) & Limit message traffic. \\  & (2) & Build location-based grouping and aggregation signature. \\ \hline Replay attack & (1) & Use time stamping technique. \\  & (2) & Include sequence number in message. \\  & (3) & MAC via ARAN routing protocol. \\ \hline  & (1) & Use variable MAC and IP addresses. \\ Node impersonation & (2) & Authentication via digital certificates. \\  & (3) & Use cryptographic certificates via ARAN routing protocol. \\ \hline  & (1) & Digital signature of software and sensors. \\ Routing attack (i.e., Black hole, Grey hole, Worm hole, and Tunneling) & (2) & Cryptographic certificate, symmetric cryptography, MAC, and one-way hash in routing protocol. \\  & (3) & Enhance the trust among different nodes. \\ \hline  & (1) & Switch the transmission channel. \\ Spoofing and jamming attack & (2) & Use the frequency hopping technique. \\  & (3) & Switch between different wireless technologies. \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Summary of common cyber physical attacks on cooperative vehicles. vehicles can communicate through V2V to form/maintain a platoon without much involvement of infrastructure, such as RSU. The capabilities of the infrastructure have not been fully exploited, yet. However, a report from USDOT indicated that platooning probability on highway could be higher than 70% in the future [106]. In this case, the cooperative driving frequently exchanges periodic safety beacons to maintain the pattern, while individual driving may broadcast event-driven messages. The heterogenous driving patterns would impose a great burden on vehicle communication and stringent requirements on transmission scheduling. Given that cyber-attacks on inter-vehicle systems mainly decease the communication availability or reliability, how to effectively allocate the communication resources and improve the communication reliability for the heterogeneous driving patterns would be a key problem. Currently, some work has studied the strategy of allocating resources, avoiding collision, and ensuring communication availability and reliability under the assistance of infrastructure (e.g., RSU, cloud). For example, the authors of [107] utilized the capability of infrastructure to combine TDMA and CSMA/CA scheduling to guarantee the timely and reliable message delivery for the heterogeneous driving patterns. In [108], cloud was introduced to assist safety massage dissemination in VANET-cellular heterogeneous networks. In fact, infrastructure would play a critical role in channel allocation, caching, content download, data aggregation/dissemination, hands-off, location, routing, and security of vehicular communication in the future [109; 110]. If the infrastructure was compromised by cyber-attacks, it would cause large-scale damage. Meanwhile, the infrastructure may adopt different architecture besides incorporating existing devices, such as the cooperative architecture, virtual architecture, etc., which leaves it vulnerable to many cyber-attacks, too. Therefore, defending infrastructure against cyber-attacks will be a great challenge.