# Privacy-Preserving Solutions in Blockchain-Enabled Internet of Vehicles
## 6 Privacy-Preserving Blockchain-Based Solutions
### Authentication  
There have been several works published in the area of blockchain-based pseudonym management and authentication in vehicular networks and they are presented below. [PERSON] et al. [28] introduced DAIA, a system that can ensure identity authentication and privacy. DAIA is based on a permissioned blockchain and provides a dynamic pseudonym using a tamper proof device. The main participants in this system are a Certification Authority (CA), Roadside Units (RSUs) and vehicles. CA as master node manages the blockchain network and the new block generation and is responsible for the secure parameters' selection. Moreover, it acts as the primary node in the consortium, records all the information and publishes the public information of RSU and tracks malicious vehicles and keeps a list of them. It is assumed that it is a trusted entity and can backtrack the identity of a malicious vehicle. RSUs are spread across the road and can manage the vehicle in their range. They are wired connected with the CA and wireless with the vehicles. They can download the malicious vehicle list from CA and it is considered as semi-trusted. Vehicles are equipped with OBU and realistic TPD (Tamper-proof device). The OBU is responsible for the wireless communications and the TPD for the storage and management of the private parameters, pseudonyms and keys. Due to attacks the TDP must frequently change the key. The dynamic anonymous identity authentication consists of five phases: (1) Registration: CA sets the parameters, RSU and Vehicles are registered to the networks and their ids are published in the blockchain. (2) Anonymous identity generation: when a vehicle enters in RSU range the TPD creates the random pseudonym. (3) Communication: vehicle communicates with the RSU exchanging time stamped messages. (4) Tracking: when a RSU wants to trace a vehicle it sends a message to CA. Then, CA writes the vehicle in the malicious list. (5) Update system keys: when system keys expire it drops them and creates new ones. The overall DAIA system is built up to be resistant to the following attacks: (i) Unlinkability: the true identity of the vehicle is stored to CA so an attacker cannot obtain the keys; an RSU does not carry any sensitive vehicle information. (ii) Non-repudiation: the vehicles cannot deny the message they send. (iii) Strong privacy protection: even if all the RSUs are compromised, the identities of the vehicles are stored with hash functions. (iv) Realistic TPD assumption: the TPD changes the keys frequently, so it is difficult to be compromised  
Figure 11: Maturity (RQ7) of the schemes presented in the papers included in our review. by side-channel attacks. (v) Man in the middle attack resistance: any attack of this type can be detected by the RSU. (vi) Efficiency analysis: the efficiency of the system is ensured by the ECDLP. Security analysis and simulation have shown that the proposed scheme is slower that others but achieves better security and strong privacy-preservation which make it suitable for practical VANET environments. [PERSON] et al. [29] suggested a scheme for vehicle authentication and privacy preservation called BlockaAPP. Based on private blockchain technology, this system consists of four entities. The first entity is the vehicles. The second entity is a registration server, which is responsible for managing and validating vehicle's ID. The verification of the vehicles is carried out by the third entity, called Service Provider. Moreover, there are multiple service providers in order to supply different services to vehicles simultaneously. The last entity is the blockchain. A trusted authority gives access to the blockchain, where service providers can read and write, in contrary of the registration server which can only write to the blockchain. The trusted authority is the only one that has the ability to read the blocks and transaction timestamps in order to trace any malicious activities back to the real ID. The proposed system works in three phases. The first one is the registration phase.