## 2 Related Work
### Blockchain Solutions for VANETs, Trust Models, Cyber Attacks, and Mitigation Strategies  
Vehicular ad hoc networks (VANETs) are a specific form of mobile ad hoc networks (MANETs) that connect vehicles on the move. The main goal of VANETs is to provide road safety, traffic management, and various infotainment services. Due to the critical nature of these services, data security, privacy, and reliable communication are of paramount importance. However, the highly dynamic and distributed nature of VANETs presents unique challenges to maintaining these aspects. Traditional security measures are often inadequate due to the absence of a fixed infrastructure, high mobility, and the heterogeneous environment in VANETs [28]. Vehicular ad hoc networks (VANETs) are highly susceptible to various forms of attacks [29], including denial-of-service, impersonation, and the spread of false information, among others [30; 31]. Traditional security mechanisms often fall short with respect to adequately securing these networks due to their unique characteristics such as high mobility and varying node densities. Public key infrastructure (PKI) has been widely used but comes with limitations when dealing with high-speed, short-range vehicular interactions [32; 33]. Traditional PKI systems are predicated on the assumption of relatively stable and prolonged interactions between entities. However, VANETs are characterized by high-speed movement and fleeting encounters between vehicles. This dynamic nature can lead to several issues with PKI, such as the following:  
* Rapid Change of Context: The fast-paced environment can outpace the PKI's ability to update and validate certificates, thereby leading to delays or errors in authentication. * Scalability Concerns: The sheer volume of high-frequency interactions requires a PKI system to handle a significant number of certificate validations within a minimal time frame, which can form a scalability bottleneck. * Latency in Certificate Revocation: The time-sensitive nature of revoking compromised certificates can be at odds with the quick interaction times, thereby potentially allowing unauthorized access. Blockchain technology has recently shown promise in enhancing VANET security by providing a decentralized approach that could potentially solve many of the challenges associated with traditional architectures [34; 35]:  
* Decentralization: The blockchain operates on a peer-to-peer network that inherently supports the dynamic and decentralized nature of VANETs, thereby facilitating faster and more efficient verifications. * Immediate Validation: Transactions and communications in a blockchain network can be validated in real time, which aligns well with the high-speed requirements of VANETs. * Immutable Ledger: The blockchain ledger [36] provides a tamper-proof record of all transactions, including authentications and data exchanges, thereby enhancing trust in vehicular communications. Various studies have investigated the application of blockchain technology in managing secure and reliable data exchanges in VANETs. In the following Figure 1, a general view of the blockchain-based architectures in VANETs is presented. As can be seen, while input communications in blockchain networks require a specific cryptographic configuration and service interface (only deployed in the RSU), output validated data are published as public events (output flows in the blockchain networks can only be managed as events), and the vehicle node can capture that information without the intervention of the RSU. On the other hand, the evolving field of trust computation offers several approaches for improving VANET security [37]. Methods for calculating trust [38; 39] can be broadly divided into categories based on multiweight fusion [40; 41], Bayesian inference (BI) [28; 42; 43], Dempster-Shafer (D-S) theory [44], fuzzy logic [45; 46], and three-valued subjective logic (3 VSL) [47; 48].