# VANET Secure Reputation Evaluation & Management Model Based on Double Layer Blockchain
## 1 Introduction
Therefore, social networks can be established through frequent communication. However, there are still many vehicles that travel irregularly, such as the ride-sharing cars (Uber, Didi, etc.) and transportation vehicles that require driving across districts or cities, making it difficult for them to establish a frequent and stable communication network. The historical database of these kinds of cars will cause a huge waste of computing power and storage space. In VANET, the different preset reputation levels of vehicles, the degree of impact of reported events, the quantified observation values of the reported and verified credibility of events, and the calculation methods of various parameters are all key issues to be considered in designing the model. In addition, characteristics of VANET, such as the real-time and high mobility make traditional solutions difficult to implement. The emergence of blockchain technology has provided a large number of innovative solutions for the security issues of VANET. Blockchain is a novel exploration of network world operating rules and technologies [11]. Following the creation of a new typical cryptocurrency,  
Bitcoin was proposed [12], and scholars noticed the advantages of the blockchain in the realization of security. In blockchain-based networks, data are stored in blocks in the forms of distributed ledgers, and are protected cryptographically. Each node can hold a full/partial copy of the blockchain. By combining the reputation evaluation and management model with the blockchain, using its advantages of decentralization, irrevocability, traceability, transparency, autonomy, and anonymity, the problems existing in the model can be well solved. At present, some researchers have tried to combine blockchain technology with the VANET reputation management model, but there are still the following unsolved challenges, including:  
1. Trust is the current judgment of an observation result generated by node interaction, while reputation is the long-term accumulated trust results of a node. In the existing VANET reputation and trust evaluation scheme, there is no good distinction between them. VANET network has its own structure of high mobility, frequent connection, and dynamic topology. Meanwhile, a bunch of vehicles cannot establish frequent and stable interactions with some fixed \"social partners\". Trust evaluation schemes of VSN based on the historical interactions of nodes are mostly oriented towards mutual trust and do not carry out quantitative calculation on the reputation of the nodes themselves. Furthermore, some researchers have tried to integrate VANET trust management schemes with blockchain technology. To our knowledge, there is no reputation evaluation scheme based on blockchain technology that fully covers the entire reputation updating process, including trust generation, record, and the conversion of trust values into reputation;
2. Bayesian inference uses existing evidence to predict unknown evidence from the perspective of probability, and has been widely used in the trust evaluation of VANET. In the use of Bayesian inference, the similarity of direct comparison information between nodes is mostly adopted to obtain prior distribution, that is, the binomial distribution is directly used as prior distribution. If the information received is the same as self-observation, trust will be obtained, while if it is different, distrust will be obtained. However, due to the differences in vehicles' speed, distance, and other factors in the actual scenarios, there will always be errors in the observation of an event in different states. Therefore, it is necessary to consider how to integrate various factors, and then compare the reliability of observation content on this basis to prevent misjudgment;
3. Existing schemes consider the indirect trust of neighbor nodes based on security. Assuming that the vehicle node \(v_{j}\) needs to judge the reliability of node \(v_{i}\), \(v_{thr}\) is a series of neighboring nodes that provide indirect trust.