## 3 Blockchain-Enhanced Security and Operational Efficiency in VANETs
### Architecture Overview
#### 3.1.2 Blockchain Layer  
This layer employs two specialized consortium blockchains (see Figure 5) in a dual-layer blockchain architecture: the event chain and the reputation chain. The proposed architecture represents a significant innovation in managing security and efficiency in vehicular ad hoc networks (VANETs) [26; 76]. RSUs and selected vehicles with surplus computational capacity are chosen to engage in the blockchain consensus process. Figure 4: Architecture of the vehicle and network layer. Figure 5: Architecture of the blockchain layer. The blockchain layer serves as the backbone for secure, transparent, and immutable data management within the vehicular ad hoc network (VANET). This layer deploys two types of specialized consortium blockchains: the event chain and the reputation chain. The event chain is primarily responsible for capturing real-time events occurring within the VANET. This could range from traffic updates to accident reports. It is primarily responsible for recording all vehicular events and transactions within the VANET. This includes data like vehicular movements, speed, location updates, and other relevant interactions. Each event recorded in this chain undergoes rigorous validation processes to ensure authenticity and accuracy [77]. Roadside units (RSUs) and certain vehicles equipped with enhanced computational resources are responsible for validating these events before they are added to the event chain. The blockchain's decentralized nature ensures that the information is reliable and tamper-proof, thereby facilitating more effective emergency responses and traffic management. The reputation chain focuses on maintaining a comprehensive and immutable record of the reputation scores for all vehicles within the network. It leverages multifactorial Bayesian inference and historical data analytics to evaluate node behaviors. This chain dynamically updates reputation scores based on the nodes' actions and interactions recorded in the event chain, thus maintaining a real-time and reliable reputation management system. These scores are computed based on various factors, such as driving behavior and adherence to traffic laws. The reputation data assists in assessing the reliability of the data transmissions and is crucial for various applications like collaborative sensing and cooperative driving. Both the event chain and the reputation chain employ a customized consensus algorithm tailored for VANETs. RSUs and selected vehicles with additional computational capacity are predesignated as validators. These validators engage in the blockchain consensus process, which may involve mechanisms like proof-of-stake (PoS) or Byzantine fault tolerance (BFT) to verify transactions before they are appended to the respective chains. In addition, we have adapted the blockchain technology to meet the requirements of VANETs, thus providing a robust foundation for secure vehicular transactions and interactions:  
* Optimized Block Generation and Hashing Mechanisms: A cornerstone of our adapted blockchain platform is the optimized block generation protocol. Each vehicular transaction is encapsulated into blocks, which are structured via a consensus algorithm tailored for high-frequency, low-latency vehicular data. The SHA-256 cryptographic hash function is employed to ensure the integrity of these blocks, thus creating an unbreakable chain of data that is resistant to tampering and fraud [19]. The blockchain platform is equipped with an advanced data retrieval system that interfaces seamlessly with the distributed ledger. This system maintains the uprightness of data, with each node validating and mirroring the complete blockchain ledger, thus ensuring the highest level of data veracity and redundancy [11]. * Customized Smart Contracts: To cater to the dynamic nature of VANETs, the blockchain platform incorporates smart contracts designed to automate and streamline vehicular processes such as real-time traffic data sharing, automated toll collection, and vehicular status reporting [9].