## 2 Literature Study  
_Different security and privacy solutions have been_ proposed for the CAVs both with and without using blockchain technology. This literature review will highlight the major contributions of both. CAVs are susceptible to both active and passive cyber attacks. During active attacks, the main intention of the attacker is to change/destroy or modify the system. Direct attacks bring more damage to CAVs security and pose a high threat to privacy protection, whereas passive attacks read data communicated between a vehicle and destination such as RSU, which poses a lower threat as compared to active attacks. Passive attacks are generally quite difficult to identify because attackers do not change the contents of the message, since both sender and receiver are unaware of the man in the middle [9]. Types of direct attacks are message spoofing, replay attacks, DDoS, and Eclipse attacks, whereas passive attacks are eavesdropping/release of information and traffic analysis. Cryptography is the most commonly used security and privacy-preserving technique used for CAVs. The literature shows different studies where cryptography has been used to propose security and privacy solutions. A secure and authenticated key management protocol (SA-KMP) using symmetric keys is used to reduce the computational cost as compared to asymmetric cryptography [10]. The trust cooperative transmission protocol for multiple-hop broadcast has been proposed, which selects the best relay that minimizes the function of a finite number of metrics among all the relays [11]. An anomaly-based intrusion detection system (IDS) known as Clock-based IDS has been implemented for measuring and exploiting the intervals of the systematic and periodic in-vehicle messages to fingerprint the ECUs [12]. A light-weight intrusion detection algorithm for in-vehicle networks works effectively and is based on the analysis of the time interval of Controller  
Figure 1: Conceptual Diagram of Proposed System. Area Network (CAN) messages [13]. An identity verification technique has been introduced based on the blockchain using symmetric and asymmetric encryption [14]. The proposed system requires an extensive verification of vehicles, RSUs, and blocks before being part of blockchain. The proposed technique is effective in providing privacy protection but at the same time is quite time-consuming. A blockchain-based decentralized platform is introduced with the name EVChain for sharing charging credits within the electric vehicle (EV) charging market [15]. The main intention of the proposed system is to share the charging credit by hiding the real identities of vehicles' owners through the k-anonymity privacy-preserving technique. However, since the model utilizes different blockchains, it may require some time for processing the user requests. The intrusion Detection System (IDS) for VANETs works to detect false information attacks using statistical techniques quite accurately [16], but it does not take into consideration the communication data. Tri-Blockchain architecture has been proposed for intelligent vehicular communication [17]. The proposed scheme is mainly designed for communicating highway accident cases to nearby vehicles and the authorities. It is based on a consensus mechanism, which means that information is verified by many vehicles and becomes part of a block to be added to the blockchain. However, a group of malicious vehicles may be the part of the consensus process, allowing for false traffic information to be communicated to nearby vehicles and the blockchain. This can make the proposed scheme less reliable. Blockchain-based secure device-to-device communication architecture is proposed using the Bloom Filter [18]. The proposed system is intended to prevent cyber attacks in military networks. Every vehicle is required to be registered with respective unmanned aerial vehicles (UAV) using their respective MAC addresses and in return, an alias is generated for them. The alias is used for communication instead of real identities.