# Blockchain-Based Authentication in Internet of Vehicles: A Survey
## 4 Blockchain-Based Authentication Schemes in Vehicular Networks
### Consortium Blockchain-Based Authentication Protocols
During the consensus phase, one of the AMs acts as a \"Speaker\" which is responsible for initiating the consensus process while the rest serve as the congress members who participate in the voting scenario initiated by the Speaker. Finally, the certificate update phase which supports two scenarios: the ability to move from one fog area to another transparently without the need of re-authentication and certificate update upon a vehicle's request. The Random Oracle Model (ROM) [134] and AVISPA tool [135] are deployed for formal security verification which proves the resistance of the proposed scheme against DDoS, replay, man-in-the-middle, identity theft, traffic analysis, masquerading, and session key disclosure attacks. Additionally, an extensive performance evaluation shows its efficiency in terms of computation, communication, and storage overheads. The authors in [136] proposed an approach to address both anonymous authentication and efficient revocation of vehicles in VANETs through the use of pseudo-ids, blockchain, and revocation tags. The scheme defines three types of nodes, namely, a supervisory node which is the Traffic Department (TD), accounting and revocation nodes represented by the multiple TAs, and verification nodes which are the road-side units. The proposed scheme is composed of four phases: initialization, registration, mutual authentication, and expeditious revocation. The privacy of vehicles during authentication is preserved by using the pseudo-ids granted to them by the RSUs. When an RSU generates a pseudo-id for a vehicle during the registration phase, the RSU stores it into a Trusted Cloud Server (TCS) and transfers a pointer referring to the storage location of the pseudo-id to the corresponding TA. The TA then forms a transaction with the vehicle's registration information including its public key certificate, the pointer to its pseudo-id stored in the TCS, and a unique Transaction id (TID) and uploads it to the blockchain. Using this TID, the identity of a vehicle can be later authenticated by viewing the corresponding records in the blockchain. This arrangement in which the blockchain keeps only pointers to the pseudo-ids while the pseudo-ids themselves are kept in the unlimitedly huge TCS improves the scalability of the system. In addition, an illegal vehicle can be determined by checking whether its pseudo-id has a revocation tab instead of looking up the whole certificate revocation list which greatly reduces the computational overhead. Further, detailed security analysis proves that the proposed scheme can resist replay attacks and prevent single point of failure problem. The authors in [137] addressed the interference issue caused by the continuous key updating in large-scale VANETS environments by proposing a blockchain-based framework for secure authentication and efficient group key updating in edge computing-enabled VANETs. They proposed a mutual V2R authentication scheme that employs certifiateless cryptographic mechanisms in order to avoid the key escrow issue. The system model consists of a cloud layer which serves as a trusted authority, an edge layer represented by the distributed RSU clusters, and a user layer of OBUs. The scheme is composed of two phases: offline registration phase and authentication phase in which each RSU authenticates a group of vehicles simultaneously as a batch which helps significantly in reducing the computation cost. Elliptic curve cryptography, one-way hash function, and bilinear pairing are utilized for generating secret key pairs and session keys during the offline registration phase and for securing communication during the authentication process. In the authentication phase, the shared session key of a vehicle is constructed independently which helps mitigate the interference in the regular V2 Rdata exchange. In addition, an efficient group key management mechanism that employs the Chinese Remainder Theorem (CRT) [138] is suggested by the authors for reliable and secure V2V communication.