# Blockchain-Based Authentication in Internet of Vehicles: A Survey
## 4 Blockchain-Based Authentication Schemes in Vehicular Networks
### Public Blockchain-Based Authentication Protocols
Their approach depends on the assumption that the smart vehicles are equipped with PUF components that generate hardware fingerprints which serve as unique identities replacing passwords and secret keys. The authentication process passes through two phases, namely the setup phase and data transfer phase. The vehicle's registration process is performed during the setup phase, where each vehicle is given a pair of public and private keys and allocated an account address in the blockchain. A smart contract named \"enforcer\" is utilized to initiate the communication between the vehicles and the blockchain whereas the RSUs serve as the blockchain miners and the certificate authority as well. When a vehicle generates data traffic, the enforcer first checks its existence in the list of registered vehicles stored in the RSUs. If it is registered, a PUF challenge is then sent to the vehicle. If the vehicle succeeds in this challenge, the authentication is completed successfully, and a communication link is established between the vehicle and the local blockchain. A digital certificate is then issued by the RSU to the vehicle to serve anonymity and privacy preserving purposes for future authentication process. After registration and successful authentication, a vehicle can communicate with other entities in IoV environment and exchange data in the data transfer phase. The deployed dPoW consensus mechanism allows the protocol to scale based on the incoming traffic generated by the vehicles and their use of PUFs makes the vehicles immune to physical and impersonation attacks. A detailed analysis is conducted through software implementation and NS3 simulation tool to evaluate their scheme in terms of the four-way tradeoffs of distributed systems which are scalability, decentralization, security, and latency. Two types of delay were measured: (1) the authentication delay at the RSU, which is time needed to authenticate a vehicle by the RSU and (2) the time to finality, which is the time needed to form a block, mine it, and reach a consensus on the mined block. The results show that their authentication scheme efficiently satisfies all the above-mentioned four properties without sacrificing any of them. The authors in [123] designed a novel blockchain-assisted authentication scheme for Artificial Intelligence (AI)-envisioned IoV-enabled smart cities called \"BBAS-IoV\" by which authentication is performed both individually and in batches. The network model is composed of several smart cities; each is managed by a separate Trusted Authority (TA) and divided into multiple clusters. Each TA is responsible for initializing the system parameters during the initial setup phase, registering RSUs and vehicles within its service area during the registration phase and distributing certificates and private/public key pairs later to them. The model contains a fog server connected to each group of geographically related RSUs and a group of cloud servers forming the publicly accessible blockchain center. Beside the setup and registration phases, the protocol has other six phases, namely, message signing, authentication, group key management, blockchain formation, AI-based secure big data analytics using blockchain and dynamic nodes addition. During the authentication phase two types of authentications exist, i.e., V2V and batch authentication. The V2V authentication enables each vehicle to authenticate its neighbors in its cluster in the smart city. The batch authentication is then used by the RSU to authenticate all its clusters' vehicles simultaneously which saves time and reduces the computation overhead of the whole scheme. After that, a group key is agreed upon and granted to each cluster to be used for securing communication among intra- and inter-cluster vehicles and their managing RSU.