## 3 Related Work
### Blockchain-Based Decentralized Data Management  
Blockchain is a very good option for implementing distributed architecture. So far, a few works have been represented on Blockchain in VANET. [PERSON] et al. proposed a distributed trust management system for vehicle network based on Blockchain technology. In this system, vehicles use Bayesian inference models to confirm received messages from other vehicles. Thus, each vehicle can produce report message for other vehicles and RSUs can calculate trust values. Finally, a trust value is stored in the blocks to improve traffic safety in an unreliable VANET [33]. [PERSON] has employed Blockchain for Smart Internet of Things (SIoT) without any human intervention. SIoT categorizes and shares information based on social trust values. This network is fully distributed, and the Blockchain platform has been proposed to provide security for manufacturing operations [34]. [PERSON] explores how to use Blockchain in VANET and takes into account the distributed storage approach and security in bulk data generated by vehicles. He presents a model in which several types of nodes (i.e., cars and RSUs) are existing [35]. [PERSON] et al. used the Blockchain consortium and intelligent contracts for storing and sharing secure data in VANET. Their system prevents the sharing of unverified data. In addition, they introduced a method for data sharing based on reputation, which is a logical triple model based on the frequency of interaction, real-time event, and the similarity of the vehicle's direction. Consequently, vehicles can achieve more qualitative data [36]. [PERSON] et al. have used of tangle technology to improve the safety and efficiency of cars in the VANET. They introduced and analyzed tangle as a solution to the Blockchain problems in the VANET [37]. [PERSON] et al. proposed a Blockchain-based structure for VANET that miners are selected based on their cooperation in this system. Selecting miners in this system is done based on the level of reputation and availability. Furthermore, to encourage miners to participate in the block validation, a contract is set between the active and standby miners [38]. [PERSON] et al. designed an M2M-REP system to protect the privacy of independent devices in the network. This system provides a condition that does not allow malicious nodes to manipulate people's message reliability and thus increases the overall trust of the computations [39]. [PERSON] and [PERSON] have proposed a hierarchical identity-based encryption mechanism according to a Blockchain infrastructure, they provided a structured model based on Blockchain for data usage to more availability and privacy. Their model is based on audible contracts in the Blockchain infrastructure and can protect privacy and confidentiality of information [40]. In a different work, [PERSON] et al. provided a safe payment mechanism in VANET based on Blockchain, which protects user information during period of data sharing time. Their proposed mechanism involves processes for storing data based on Blockchain technology and supporting anonymity [41].  
The mentioned studies guarantee the security of storage data by Blockchain solution. Despite this advantage, one of their significant shortcoming is low transaction throughput and small scalability, while in VANET there are great number and high speed of generated transactions. In this study, we propose a novel method based on the Sharding algorithm to overcome this shortcoming.