## 3 Security Issues Facing CVs and Solutions
### Bluetooth  
Bluetooth is a type of short-range communication (typically tens of meters) and was proposed to be applicable for the communications of CVs in some certain situations. For example, at a traffic intersection, Bluetooth can be used for connecting vehicle communication to avoid potential accidents [36]. Another scene is that Bluetooth may be applicable to V2P communication due to its low energy consumption, considering that pedestrian users in V2P usually have the limit on power saving of the device. However, as Bluetooth is natively developed for short-range low-speed transmission, it would be challenging when it is applied in highly mobile vehicles' communication, which has the requirements of high transmission data.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Components** & \multicolumn{2}{c}{**Application**} & \multicolumn{2}{c}{**Security Issues**} & \multicolumn{2}{c}{**Solutions**} \\ \hline \multirow{4}{*}{CAN bus} & (1) & CAN-C: high-speed bus that & \multirow{2}{*}{(1)} & Eavesdropping and & \multirow{2}{*}{(1)} & Strong authentication \\  & & connects the engine, brakes, & traffic analysis. & & & between different entities, \\ \multirow{4}{*}{CAN bus} & (2) & CAN-HIS: low-speed bus that & \multirow{2}{*}{(2)} & \multirow{2}{*}{(3)} & \multirow{2}{*}{(3)} & \multirow{2}{*}{(3)} \\  & & connects the comfort systems and & & & & including exterior devices. \\ \multirow{4}{*}{} & (1) & \multirow{4}{*}{CAN-HIS: low-speed bus that } & \multirow{4}{*}{(2)} & \multirow{4}{*}{(3)} & \multirow{4}{*}{(2)} & \multirow{4}{*}{(3)} \\  & & climate controls. & & & injection. & \\ \hline \multirow{4}{*}{ECUs} & (1) & Powertrain. & \multirow{4}{*}{(1)} & Monitor the real-time state of the & \multirow{4}{*}{(1)} & Fuzzing, phishing, DoS, etc. \\  & (2) & Chassis. & & corresponding component. & \multirow{4}{*}{(2)} & Overwriting firmware and \\ \multirow{4}{*}{} & (3) & Infotainment. & \multirow{4}{*}{(2)} & Control the components. & & flashing ECUs. \\ \cline{1-1}  & & Body control. & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 2: Summary of the security issues and solutions for the CAN bus and ECUs.  
In recent years, a few techniques have even been used to enhance the security of Bluetooth communication, including frequency hopping, a pre-shared key for authentication, and encryption [37]. Even so, some security risks cannot be avoided, yet, when Bluetooth is used in vehicles' connectivity. Table 1 lists the applications and potential security issues of Bluetooth. In nature, how to handle the native security risks caused by the frequent iteration, various versions of Bluetooth, and pairing methods would be challenging. As a matter of fact, the reason why Bluetooth is so convenient to use in the first place is that it constantly broadcasts information such that nearby devices can be alerted to its presence. Thus, setting the Bluetooth device to \"undiscoverable\" mode would be a securer measure.  
Bluetooth devices can form piconets, and multiple piconets through sharing the same devices can join to form a scatternet. If an entity is compromised, it is possibly going to infect other piconets or the scatternet, which finally damages multiple entities in the V2X connection. In addition, the MAC address of a Bluetooth device is usually unique and traceable, which may expose the vehicle to traceability attacks [6]. Even though a Bluetooth PIN is used between the paired Bluetooth devices to implement authentication, it is vulnerable to brute-force decryption, interception, and injection of a fake PIN [38]. What is worse, the compromised device can inject malicious messages into the paired vehicle and damage its functions. In [39], the authors showed how a user device connected to a vehicle through Bluetooth launches an attack on the vehicle. In [40; 41], the authors investigated how Bluetooth-enabled devices are extremely vulnerable within and beyond the vehicle domain.