## 3 Blockchain-Enhanced Security and Operational Efficiency in VANETs
### Architecture Overview  
The proposed model has been meticulously designed to facilitate the secure storage, dependable updating, and efficient retrieval of reputation metrics [72], which are pivotal in ascertaining the reliability of vehicular entities in VANETs. Our methodical exploration is underpinned by the need to bolster the security mechanisms that underlie the robust transmission and exchange of data. The innovative framework we introduce transcends the traditional VANET paradigms by incorporating a dedicated focus on the authentication and verification processes that are critical in a network where high-speed dynamics and transient interactions are commonplace. Figure 2 depicts our multilayered architecture, which is stratified into four integral triers: the vehicle layer, network layer, blockchain layer, and infrastructure layer. Each stratum is meticulously crafted with distinct functionalities and components that synergize to assure the integrity of data dissemination, the reliability of communication, and the overarching security of the network. Core elements such as vehicular nodes, roadside units (RSUs), blockchain networks, and infrastructural elements are interwoven within these layers. Our framework anticipates and addresses the complexities associated with the confluence of blockchain technology within extant VANET systems, which is a concern highlighted in recent scholarly discourse [6]. While we acknowledge RSUs as potential single points of failure, their presence in the system architecture is justified by the substantial benefits they offer in terms of network coverage, data aggregation, and performance enhancement. RSUs are strategically positioned to facilitate communication and data exchange between vehicles and the network infrastructure. They serve as pivotal relay points that extend the communication range,  
Figure 2: Comprehensive representation of the multilayered VANET system architecture. augment network robustness, and enable a broader dissemination of critical information, such as traffic conditions and safety messages. To mitigate the risk associated with a single point of failure, our proposed solution incorporates blockchain technology to decentralize data management and ensure redundancy. The blockchain operates as a distributed ledger that records all transactions and interactions, thereby not solely relying on RSUs for data integrity or network functionality. In the event of an RSU failure, the blockchain layer maintains continuous operation, thereby allowing vehicular nodes to communicate directly with each other or with alternative RSUs without disruption. Figure 3 illustrates the decentralized nature of the blockchain, thus enabling direct V2V interactions without necessitating RSU intermediation for every transaction. This approach, however, also introduces a new challenge: how to ensure the validity of data shared directly between vehicles. In fact, our data validation process is designed to address this challenge. It is a two-step process:  
* Vehicle-To-Vehicle (V2V) Validation: When a vehicle receives data from another vehicle, it first performs a basic V2V validation check. This check includes verifying the data signature, expiration date, and consistency with the vehicle's own knowledge of the world. * Blockchain-Based Validation: If the data passes the V2V validation check, the vehicle then broadcasts it to the blockchain. The blockchain then performs a global validation check. This check includes verifying that the data have not been previously broadcast and that they are consistent with the data that other vehicles have broadcast to the blockchain. If the data passes both the V2V and blockchain-based validation checks, they are considered to be valid and are added to the blockchain. This two-step validation process ensures that the data shared directly between vehicles are valid and reliable. It also prevents malicious vehicles from broadcasting fake or misleading data to the network.