# Privacy-Preserving Solutions in Blockchain-Enabled Internet of Vehicles
## 6 Privacy-Preserving Blockchain-Based Solutions
### Authentication
In this phase, to avoid identity spoofing and to preserve its privacy, every vehicle sends an encrypted message to the registration server and a trusted authority checks and exchanges their real ID with a pseudonym. This pseudo-id will be used for any future communications for one session. After a successful exchange, the registration server adds the necessary details of the transaction in a block and dumps all the other so that real ID cannot be retrieved. During the second phase which is called authentication phase, the vehicles send their pseudo ID and the requested services to the service providers. The service providers accept or decline the requests. Then, they add any valid or not request to the blockchain. The third and last phase is the authorisation phase. For every offered service, the service providers maintain a pair of private and public keys, in order to identify the service and the transactions. The vehicle sends a request message and its digital signature that is created using its private key. The service providers check the request message and add the transaction to the blockchain, whether it comes from a valid vehicle or not. For the exchange of keys, the proposed system has considered an asymmetric key cipher and the validity of the transaction is ensured using a consensus protocol. During registration phase, RSU, vehicles and cloud server act as intermediate access point to the registration server and to the service providers during authentication and authorisation phases. The authors built their system on a permissioned Ethereum platform and the smart contracts are implemented in Solidity language using the Remix development platform. The results demonstrate that by using the permissioned blockchain, privacy can be preserved. Another pseudonym management system for IoV is VCS proposed by [PERSON] et al. [30]. In this scheme, the authors use a four-layer type of nodes. The first three layers for the service providers consist of RSUs covering geographically all the roads, PMs (Private Manager) both with wireless communication devices, plus the RSU act as access point and Public key Infrastructure (PKI), containing Certificate Authority (CA), Anonymity Server (AS) and any other third party infrastructure, where all the pseudonym and cryptographic materials are created. The fourth layer called service user consists of the vehicles equipped with computerised device known as On-Board Unit (OBU). The PKI is isolated and generates all the cryptographic material to link the real identity to the pseudonym of the vehicle. The pseudonyms are not permanent, but they change after a period of time. Moreover, all these cryptographical materials must be kept in a secured facility to ensure the privacy and security requirements. The central managers can be accessed only for the initial registration of the vehicle and for revocation of a certificate, in case of malicious behaviour or identity compromise. In this proposed system, the PM are shuffling the pseudonyms and the PKI can keep track of the pseudonyms related to original identity, by keeping the transaction in a disturbed ledger, making the revocation of a certificate in the shortest possible time. The new revocation list will be broadcasted to the vehicle nodes. For the blockchain network to work properly, some assumptions are made: (1) Role of the miners: PM take the role of the service user and miner as they have powerful computation power to maintain the blockchain and do the block mining since there is not any reward, featuring in classic blockchain networks. (2) Approximate Mining Synchrony: to limit the deadline for each transaction collection interval, all the PMs start the mining at the same time, using a synchronised clock. (3) Consensus: the adapted consensus is Proof-of-Work, since it is the only one efficiently tested against security manners.