# Privacy-Preserving Solutions in Blockchain-Enabled Internet of Vehicles
## 6 Privacy-Preserving Blockchain-Based Solutions
### Data Exchange
DAG is updated asynchronously by vehicles and is periodically synchronised to the main blockchain. Two types of transactions are recorded to the main blockchain: data sharing between vehicles and the summary of transactions in DAG. In order to ensure the quality and integrity of shared information, verification is carried out in two stages, firstly by vehicles involved in local DAG and afterwards by RSUs in the main blockchain. Deep Reinforcement Learning (DRL) and Deep Deterministic Policy Gradient (DDPG) algorithms are used to select vehicles with most resources, which act as verifiers in blockchain network. The consensus algorithm used in blockchain is Delegated-Proof-of-Stake (DPoS). Blockchain and federated learning are used to protect the vehicles' privacy and to utilise the limited resources. Through evaluation of the model's performance and comparison with other two baseline methods, the authors have proved that the proposed model is accurate and efficient. [PERSON] et al. [51] proposed a privacy-aware content caching architecture in CIoV based on blockchain technology. This model is separated into three layers: the first one is the vehicles, which have several sensors to collect data and upload them to the cloud. The second layer is the RSUs, which cover different geographical areas and provide data to nearby vehicles. The third layer is remote-cloud-based providers and cognitive engines which can perceive and analyse vehicles' needs so that content is provided according to vehicles' needs. Deep learning and machine learning algorithms are used to improve the procedures of analysing and perceiving the vehicles' needs. The vehicles and RSUs willing to provide contents cache the contents and then broadcast them along with the specific download time according to the needs of other vehicles. Surrounding vehicles download those contents that match to their needs via V2V or V2R communication. Thus, vehicles do not submit their content requirements when they need information, but they download the content most suitable to their needs. Therefore, no personal information is uploaded and thus the privacy of vehicles is protected. Vehicles can serve as a content provider or content receiver and can also change their role at any time. As content receivers they must pay a fee to receive contents. Experimental results have shown that the proposed scheme has high cache rate and robustness but the type of blockchain is not mentioned. Vehicles' privacy is protected, because they do not need to submit requests with their own privacy information and content requirements to RSUs when willing to receive data. In addition, because vehicles and RSUs do not trust each other, blockchain technology is used in order to protect the security and privacy of involved vehicles. Completed contents sharing are recorded as transactions by RSU and cognitive engine. RSU generates the new block which records the latest content transactions and then broadcasts those transactions to other RSUs which confirm the transactions ensuring their safety and immutability. The main characteristics of this architecture are more intelligent content requirement analysis and secure and flexible content access in shorter response time. [PERSON] et al. [52] proposed a data sharing scheme in IoV driven by blockchain technology called IoVChain. The system consists of two entities: the RSUs and the vehicles. The RSUs maintain a consortium blockchain and can host public or private data exchanged between the vehicles. Public data can be the weather or road conditions and private data could be vehicle's speed or location. The vehicles can register to the network by the RSUs, invoking a smart contract and checking the vehicles key card that holds its real information, acting as a pseudo ID. IoVChain is based on permissioned Hyperledger Fabric and take advantage of Fabric's technology called channels. Only members of a channel can read and write on the channel's ledger. Users can join multiple channels.