# Privacy-Preserving Solutions in Blockchain-Enabled Internet of Vehicles
## 6 Privacy-Preserving Blockchain-Based Solutions
### Traffic Conditions
Single verification is performed in the case of one sent message and aggregation of signatures parts of multiple ciphertexts in the case of multiple messages. Afterwards, the aggregated signature is sent to a cloud server for verification and then transmitted in ciphertext format to the blockchain. A root authority decrypts and verifies the ciphertext on the blockchain in order to respond in situations of emergency. In CFTM, The privacy and anonymity of vehicles are ensured as they are using pseudonyms during communication procedure. Only the traceability authority, which is responsible for generating pseudonyms for vehicles, knows their real identity. Thus, the identity of vehicles is protected. In addition, while communicating, signcryption is used, so the transferred data is in a ciphertext format and cannot be decrypted by fog server, nor cloud server or malicious users. Furthermore, the cloud server carries on the ciphertext equivalent test process and sends the ciphertext, which exceeds the threshold to the blockchain. The ciphertext cannot be modified or deleted after being added to the blockchain; therefore, road condition information and sensitive information of users remain immutable and are secured from malicious behaviours. Moreover, as traceability authority can trace the real vehicles' identity, it is easy to find malicious users. Formal security analysis of the proposed model and extensive comparisons with other existing models have shown that it satisfies the security requirements and works efficiently. [PERSON] et al. [45] addressed the problem of traversing between different blockchain networks, preserving the privacy of the vehicles. To achieve the above, they propose a gateway system with non-interactive zero knowledge range proof scheme (ZKRP). When a vehicle wants to leave a network and enter another's territory, it encrypts its information with the proposed ZKRP and broadcasts the request to the nearby gateway. Upon request receipt, the gateway validates the request and the vehicle connects to the new permissioned blockchain network based on Hyperledger Fabric, with the ability to start sharing data. The authors have built and tested a prototype, which shows data integrity and vehicle privacy can be maintained while switching networks. [PERSON] et al. [46] proposed a location cloaking system in VANET based on a dual-layer permissionless blockchain. Their system consists of vehicles which are the users, RAs, which are responsible to register, update or revoke the vehicle's certification and store the certifications on blockchain layer named CerBC. The certificate acts as a pseudonym for the vehicles. RSUs are responsible to manage vehicle's requests and form the clocking region with k-anonymity algorithm. Moreover, they are responsible to forward the requests to LSP. In addition, they maintain the requests of another layer blockchain named ReqBC. The LSPs are responsible to process the query requests using the query algorithm and return the queries to RSUs. LSPs do not interact directly with the users and users do not interact directly with each other. The system uses a trust reputation system based on vehicle's Querying reasonability, from space and from frequency, plus, rationally and authenticity of location information. In summary, the privacy preserved with no direct communication between entities, certifications which act as pseudonyms and cloaking location with clustering \(k-1\) vehicles. Experiments were made in Hyperledger Fabricusing PBFT consensus protocol and ECC for the cryptographic algorithm. The results show that the system can preserve privacy. [PERSON] et al. [47] proposed an identity and location privacy scheme called Trusted Cloaking Area Construction (TCAC). Using k-anonymity [63], a well-known privacy technique and a trusted third-party entity, called anonymiser, can expand the precise location area of one vehicle to a circle location, with addition of \(k-1\) vehicles as cooperative vehicles, concealing the actual location of the vehicle.