# Privacy-Preserving Solutions in Blockchain-Enabled Internet of Vehicles
## 6 Privacy-Preserving Blockchain-Based Solutions
### Authentication
The function of the VCS is described below: (i) System initialisation: the cryptographic material is generated by the PKI and transmitted through highly secured connection to the vehicle and equipment manufacturers, who install it to the vehicles. (ii) Pseudonym Shuffle: the vehicle marks the pseudonym as used and when the expiration conditions are met, the vehicle can change it, only when it enters on an agreed place named mixed zone, where all vehicles are mixed in order to minimise the ability to be tracked. The expired pseudonyms are kept for a certain period in single package, and afterwards they are shuffled and disturbed back to the PMs for reuse. (iii) Certificate revocation: the proposed system has a malicious behaviour detector; PM collects all the activity and while communicating with the network, it broadcasts all the malicious reports. Even if a PM is compromised, the blockchain network is secured, as it needs 51% of them to work properly. The proposed system is built in permissioned blockchain and has been tested in simulation, using OMNET++ with dedicated simulation packages Veins and PREXT; the simulation results find the proposed system more effective than the traditional pseudonym solutions and more resilient to privacy and security attacks. [PERSON] et al. [31] presented an authentication and message dissemination scheme for vehicular systems which contains two different blockchains, a permissioned geographical blockchain and a permissionless blockchain. The permissioned blockchain is used for authentication of vehicles within the boundary of a country. In this blockchain a trusted authority (TA) is responsible for generating new blocks which represent pseudonyms of users in a chronological order. During the registration process, a secure channel is established between the vehicle and the TA, and then the vehicle sends to TA its real identity, obtained by Motor Vehicle's Division (MVD). Afterwards, TA cooperates with MVD to check the vehicles real identity and then produce a pseudonym for that vehicle. After the successful vehicle's authentication, TA appends a new transaction to blockchain. Vehicles can only read this blockchain to check the authenticity of other vehicles. In addition, special vehicles have the role of miners while other On-Board Units have only read rights, thus malicious behaviour is prevented. The public blockchain, named RSU-BC because it acts as an RSU, is used for event messages dissemination. RSUs are replaced by blockchain, in order to achieve decentralisation of the system and avoid a leakage of private information in case an RSU is attacked. In RSU-BC every entity can generate new blocks representing event messages. Vehicles can act either as miners in this blockchain or as light nodes which are only responsible for generating messages. After a new block is generated, all cars in the system update their blockchain and can be informed for information such as road conditions and safety. In the case of a vehicle travelling in another region, the miners of the new RSU-BC check its authenticity in authentication blockchain in order to participate in the message dissemination procedure. By using geographical blockchain, consensus convergence time is reduced. In addition, because pseudonyms are stored in a blockchain, they cannot be modified by third parties. Moreover, because only trusted authority knows the association between pseudonyms and real identities and no other information is issued in transactions, privacy is prevented. During experiments' performance and security analysis, the proposed scheme was compared with previous models and proved that it requires the lowest computation and communication cost, according to the authors. A privacy preserved framework in VANET is proposed by [PERSON] et al. [32]. The proposed system is based on blockchain and pseudonymity. The vehicle obtains its real identity from Motor Vehicle's Division and communicated with a trust Certificate Authority (CA) via a secure channel.