## 4 Blockchain-Based Solutions on the Internet of Vehicles  
Given the characteristics of Blockchain and the security challenges of IoV, research and development for implementing the former in the latter have been growing over the years. Most of these implementations try to solve some security problems regarding data sharing in IoV networks. In the work of [PERSON] et al. [76], a Blockchain-based framework to provide security, safety, and transparency for users, and vehicles, in cab-sharing scenarios (e.g., Uber) is proposed. In this framework, smart contracts are used, so information is not accessed and altered wrongly by unauthorized parties (i.e., secondhand data sharing). Vehicles and IoTdevices need to be registered in the network to access its services via logging of information in a database and the Blockchain for traceability. IoT devices store their activities in the Blockchain, instead of vehicles, for ease detection of malicious behavior while maintaining a reasonable level of computational and storage costs. For the Blockchain, managers are elected (a primary and a secondary, which takes over in the case of a faulty primary) to manage the Blockchain for some time and receive registration requests from other nodes, be them vehicles or singular devices. There are also miner and peer nodes, and the former helps validate the authentication of registration requests mentioned above. The managers then verify the requesters' authenticity and generate their public keys if the authenticity is verified. Implementing a rating-based system for providers allows users to evaluate which one will be chosen to give them a ride, providing a way to incentivize good behavior from providers. Providers can also choose which user to attend to based on multiple parameters. A Blockchain is maintained between the user and the provider to detect alterations of values (e.g., geographical position, time, route, among others). The evaluation was made through a simulation in the NS2 network simulator with Blockchain techniques, aiming to get results under network congestion and compromised nodes, and comparing them with results from an already existing approach. An attacking scenario with an adversary model (i.e., malicious/hacked nodes present in the network) was utilized to test the proposed framework. Tests were made with malicious nodes passing as vehicles, IoT devices, and Blockchain nodes (miners and peers). The authors conclude that the proposed approach surpasses existing ones, with 86% success and accuracy rates, which are theorized to get higher with time due to the removal of ill-intended nodes. They also verify lower levels of network congestion with fake requests and that the possibility of attack with \(n\) compromised nodes was lower for the proposed approach. The altered amount of data, in the case of intruders messing with user's ratings, was also lower in the proposed approach. While still having some edges that need polishing, the proposed approach results achieved a 79% success rate compared with the already existing approach. [PERSON] et al. [77] presented a new scheme for vehicle registration and authentication in IoV based on Blockchain technologies, such as Ripple and BFT consensus protocols, and smart contracts, to eradicate the impact of malicious vehicles. When a new node wants to join a contract group, it applies for it and is then evaluated by each node of the group through gathered data on that node in the infrastructure. If more than 51% of the nodes accept the node's integration, it is added to the group. Otherwise, it will be added to a watchlist of suspicious nodes and following applications to the contract group will be met with more restrictive conditions. A distributed PKI system is utilized for trusted key distribution. For authentication, the vehicle sends a request to RSUs with their ID and public key. The RSU encrypts this data and sends it to the cloud service provider that, through the usage of consensus protocols, verifies the authenticity of the vehicle's identification.