# Blockchain-Based Authentication in Internet of Vehicles: A Survey
## 4 Blockchain-Based Authentication Schemes in Vehicular Networks
### Public Blockchain-Based Authentication Protocols
The blockchain formation phase is handled by fog and cloud servers in two steps; first, each fog server receives the list of transactions and their compact signatures from the associated RSUs and verifies them, if the signatures are valid, it transmits the partial blocks to a cloud server in the blockchain center. Then, the cloud servers convert the received partial blocks into complete blocks which are then mined and voted for through the PBFT consensus mechanism to decide on their eligibility to be added to the blockchain. The signature verification and block verification applied in this scheme ensures that data poisoning attacks which inject malicious transactions in the blockchain are avoided in the proposed BBAS-IoV protocol. This results in fully trusted blockchain transactions that can be a great asset for deriving highly accurate ML models and thus correct predictions and decision making can be achieved. Detailed formal security analysis using the Automated Validation of Internet Security Protocols and Applications (AVISPA) tool as well as informal security analysis is provided to evaluate the security features of the proposed BBAS-IoV scheme. The results obtained show that various security attacks namely, replay attacks, man-in-the-middle attack, vehicle and RSU impersonation attacks, privileged-insider attack, and ephemeral secret leakage attack are prevented. Extensive performance evaluation through simulation with the aid of Multi-precision Integer and Rational Arithmetic Cryptographic Library (MIRACL) reflects high efficiency of the scheme in terms of computation, communication, and storage overheads. The authors in [124] designed a blockchain-based authentication scheme for vehicular accident detection and notification in IoV-enabled intelligent transportation systems, called BCAS-VADN. The scheme deploys a cloud/edge computing framework that consists of cloud servers, edge servers, RSUs, and vehicles. The system architecture is divided into multiple clusters with a Cluster Head (CH) for each, which acts as an intermediate entity to arrange the communication between the cluster members and the RSUs. Each RSU is associated with an edge server and all edge servers are linked to cloud servers in the blockchain center through a public channel. The proposed scheme consists of five phases, namely, system initialization, enrollment, authentication, blockchain verification and addition, and dynamic node addition phases. The proposed scheme assumes the existence of a trusted registration authority that is completely responsible for initializing the system parameters including elliptic curve, one-way hash function and its own private-public key pair as well as enrolling all the entities in the network, i.e., cloud servers, edge servers, RSUs, and vehicles. The authentication phase then takes place in two steps: V2 CH authentication in which a vehicle and its associated CH mutually authenticate, then CH2 RSU authentication where the CH and its associated RSU authenticate each other. Upon a successful authentication process, each vehicle can securely report accident-related transactions to its associated CH if it detects an accident on the road. The cluster head then securely transfers the received transactions to its associated RSU which in turn sends them secretly to the corresponding edge server. The edge server prepares a partial block containing the accident-related transactions, the Merkle tree root, and a digital signature. This incomplete block is forwarded to its associated cloud server in the blockchain center forming a complete block from the received partial block. At this point, all the cloud servers in the blockchain center participate in the block verification process through the PBFT consensus and if verified, the complete block containing the vehicle accident-related information is added to the blockchain center and made available for use by other vehicles for optimal route selection and better road-related decisions.