# Privacy-Preserving Solutions in Blockchain-Enabled Internet of Vehicles
## 6 Privacy-Preserving Blockchain-Based Solutions
### Traffic Conditions
In case of an accident or a malicious behaviour, the manager can track back the vehicle through the public key in the group signature. The edge nodes maintain the permissionless blockchain and also collect data from vehicles and put them into blocks. As a consensus protocol, the authors proposed a hybrid one based on PoS and DAG, as the popular Proof-of-Work consuming a lot of processing power. Because of the continuous change of the data that the road conditions impose and until the wide use of 5G, a Time Sensitive network is the best solution at present as the authors mentioned. Security tests have been made by collecting real life data, by using iPhone 7 as smart terminal and computer with Ubuntu OS for the data processing. The data had been collected by taxis and family cars, and then the evens were edited by hand. The authentication protocol and blockchain have been tested in simulation on IBM-Watson platform, which proved than they can be used for quickly obtaining warnings and in parallel protecting a user's privacy. [PERSON] et al. [43] proposed a semi-decentralised scheme called SCTSC for privacy preservation in identity, location and data. The scheme uses a permissioned attribute-based blockchain to control traffic lights. In this scheme, in order to reduce traffic, signals of traffic lights are controlled by vehicles. Vehicles are divided into groups according to their dynamic attributes such as their location or direction. In these groups, every vehicle votes for the time of signal change and their agreement along with other related messages are encrypted and then recorded to blockchain. The procedure to reach an agreement is divided into four phases: (1) The _setup phase_, where public parameters are generated using ciphertext policy attribute-based encryption (CP-ABE) and also verification of users' identity is done. (2) The _drafting phase_, where a proposer chooses a voting group according to vehicles' attributes and poses a suggestion for signal control. A fixed number of voters is needed to reach an agreement. The threshold value is decided and stays unchangeable in next phases. (3) The _reply phase_ where a number of voters reply in order to reach an agreement. The voters verify signatures and send their replies to a recorder who appends those as records into blockchain. (4) The _decision phase_, the proposer collects all replies, decrypts their ciphertext and after checking the pseudonyms and signatures or double entries, if the number of voters is the expected, he sends the decision record to the recorder; otherwise, he continues collecting votes. Consequently, the recorder, which does not know the real identities of proposers and voters, records the agreement to blockchain by performing a cooperation consensus algorithm. In SCTSC, vehicles communicate with each other through blockchain and not directly. Other groups or traffic signal controllers can receive this final agreement without breach of users' privacy. This is achieved due to the anonymity of users who use pseudonyms during communication process. Authentication centre is responsible for verifying users' actual identities and distributing keys and pseudonyms but cannot decline any user. Trace manager is responsible for detecting malicious users by querying their pseudonyms in authentication centre. In addition, intermediate messages and other contents cannot be read by third parties outside those groups, thus privacy is also preserved inside the groups. Through extensive experiments and security analysis, the authors proved that SCTSC is feasible and effective. [PERSON] et al. [44] suggested a framework, called CFTM, which describes the monitoring of road conditions by using cloud-fog computing for location and data privacy. In this scheme, vehicles signcrypt messages by using certifiateless aggregation singcryption (CLAS) technology and then send them to RSUs which act as fog servers and also verify if the vehicle user is legal or malicious.