# Secure Trust-Based Blockchain Architecture to Prevent Attacks in VANET
## 2 Related Works  
There have been numerous security schemes proposed by various researchers to address the security and privacy issues in VANETs. This section highlights some of the existing approaches that focused on similar problems in VANET using similar techniques to the proposed solution. An anonymous and lightweight authentication scheme smart card (ASC) was proposed by [PERSON] to address privacy-preserving problems, such as legitimacy of users and messages transmitted across the network [25]. The authentication of users and messages are done using low-cost cryptographic operations. This protocol does not only verify the identity of the users and authenticate messages communicated, but it also guarantees anonymity of users. Anonymity in this scheme is achieved by dynamically generating login identities for users using smart cards to replace users' actual identity, thereby hiding the real identities of users from attackers. The dynamic login identity is updated periodically to provide anonymous authentication. The researchers also proposed a dynamic password change without depending on a trusted authority (TA), so that the scheme is resistant to various attacks such as impersonation and offline password guessing attacks. The messages in ASC are authenticated using two hash chains to minimize computation complexity. Apart from that, messages are appended with timestamps obtained from GPS devices to validate the freshness of the messages and minimize replay attacks. The performance of ASC was evaluated using VanetMobiSim in terms of communication and computation overheads, end-to-end delay, and average packet loss ratio. From the simulation, ASC was found to perform better and have better efficiency than other baseline protocols. Nevertheless, a major drawback of ASC is that the frequent update of login identity and user password will introduce higher computation cost in the network. Not only that, the frequent updating of login identity may open new opportunities for attackers to launch attacks such as impersonation or identity theft, since the login identity changes periodically, resulting in increased difficulty in detecting malicious nodes. [PERSON] proposed a decentralized lightweight authentication and key agreement protocol (LAKAP) for VANETs, which uses one-way hash functions and bitwise exclusive OR (XOR) operations [26]. The proposed lightweight protocol highlights some features: it allows dynamic road side unit addition in the network after initial deployment, provides RSU to RSU key establishment, and has anonymity and intrackability, among other additional features. Apart from that, the solution exhibits three authentication approaches: between vehicles, between vehicle and its respective cluster heads (CHs), and between CHs and their RSUs. The researchers adopted a cluster-based network model to reduce the computation and communication overheads. In this proposed protocol, the CHs are elected based on trust values and strong connectivity. Only vehicles with high trust values and strong connectivity are selected as the CHs. Each of three authentication approaches also establishes a keypair for the nodes involved. Besides this, a key is also established between neighboring RSUs to maintain secure communication using the keys. The proposed lightweight authentication scheme uses timestamps to prevent replay attacks in the network. The passwords of each vehicles are updated periodically to improve the security of the user and information. Using a computer running on Intel Xeon E5-1620 v2 processor with 16 GB RAM provided by the Faculty of Computer Science and Information Technology, Universiti Malaysia Sarawak, the performance of the proposed scheme was evaluated using Network Simulator 2.35 (NS-2.35) in terms of communication and computation overheads, throughput, end-to-end delay, and packet delivery ratio (PDR). From the analysis, the lightweight authentication and key agreement protocol was found to encounter low communication and computation costs.