# Privacy-Preserving Solutions in Blockchain-Enabled Internet of Vehicles
## 6 Privacy-Preserving Blockchain-Based Solutions
### Authentication
The users' identity privacy is protected, as blockchain prevents their identity and their car's identifier of being exposed. Furthermore, vehicles can check a pseudonym's or signature's validity, without being able to link it with the real singer, by using one-time addresses. In addition, blockchain does not record private keys, thus anonymity is ensured because identities are not exposed. Lastly, because all used pseudonyms are recorded in blockchain, malicious nodes cannot deny their committed actions. In addition, in case of misbehaving, all unused pseudonyms and their public key are revoked. Thus, the system is secure from attackers and malicious users. Lastly, through security analysis, by usingattack tree method, the authors have shown that their model is more resistant to attacks than the conventional vehicular public key infrastructure (PKI). [PERSON] et al. [34] proposed a privacy preserving scheme with trust management. Their system considers responsible the Law Enforcement Agencies (LEA) to register a vehicle to network. The RSUs are responsible to distribute pseudonyms to the vehicles, as well as to maintain a two layer permissined blockchain. On the blockchain's consortium layer are stored the pseudonyms, to preserve privacy, and the messages of the vehicles. On the vehicular layer, the vehicle's authentication is stored, as well as the trust evaluation of the vehicles. The system has the ability to change a vehicle pseudonym if requested. To prevent any data tamper, trust calculation is secured by homomorphic encryption. A performance implementation has been employed using the Performance Evaluation Process Algebra (PEPA) model showing that homomorphic encryption and pseudonymity can protect the vehicles' privacy. [PERSON] et al. [35] proposed a system based on permissioned blockchain for IoV with privacy protection. The system has three entities: LEA, RSU and Vehicles (users). The Law Enforcement Agency (LEA) is responsible for the registration of the vehicles. The owner of the vehicle must send the real information of the vehicle (like license plate number, name and type) and the LEA determines if it is legit to participate in the network in order to generate a username (pseudonym) and a pair of public-private keys and the validity period of the keys, as it must change on a regular basis to preserve the vehicle's privacy. RSUs are responsible for the communication between the vehicles and maintains the blockchain network, registering network's data. For that reason, RSUs should have powerful computation power and sufficient storage capabilities. Moreover, RSUs are responsible to detect distorted broadcasts and evaluate the vehicles, forming a reputation system. If any of the vehicles are flagged as malicious, its key is revoked and the process packed as a transaction registered into the ledger. Based on experiments, the location privacy is preserved by pseudonyms and by using encryption on the public keys. [PERSON] et al. [36] proposed a scheme for VANET based on blockchain that uses PKI to preserve privacy called BCPKI. The scheme consists of Vehicles (users) and RSUs. The vehicle must register to the network via RSU. The vehicle requests to join the network and the RSU issues a pseudonym using PKI certificates and stores it to permissionless blockchain. Authors use pseudonyms as a primary privacy preserved technique for their proposed scheme. A light-weight authentication scheme based on permissioned blockchain for VANET is proposed by [PERSON] et al. [37]. The architecture includes Authentication Parties (AP) that are responsible for ledger maintenance and registration of the vehicles. The vehicles are the users and RSUs which have a read-only access to the ledger. Upon registration AP disturbs a set of public-private key set to the vehicles, as well as a pseudo ID, called PID, to preserve the vehicle's privacy. Moreover, AP is the only participant that can trigger transactions and write on the blockchain.