# Privacy-Preserving Solutions in Blockchain-Enabled Internet of Vehicles
## 3 Related Work  
In the past few years, several surveys have focused on privacy issues in different aspects of Internet of Vehicles. The authors of [15] examine existing applications aiming to solve and improve security and privacy issues of VANETs. The authors of [14] also discussed privacy and security issues in IoV against attacks. Paper [16] discussed the relationship between personal data, consent and privacy in vehicular systems and examined existing proposals aiming to solve security and privacy issues of exchanging data. In [17], the authors focused on privacy and security solutions for 5G vehicular networks. The authors of [18] presented the most common security attacks and discussed important security mechanisms aiming to prevent these attacks and protect the privacy of vehicular systems.  
Some of the existing surveys have focused on authentication schemes in VANET. The authors of [19] conducted a survey on authentication methods proposed for VANET aiming to better preserve privacy. The authors of [20] analysed anonymous authentication mechanisms aiming to provide privacy protection and discussed several trust management models for VANET. Additionally, the authors of the survey [21] focused on authentication and privacy issues that can occur in VANET during message dissemination. For that reason, they conducted a comparative study of proposed schemes over the last ten years which aimed to address those issues. They analysed and compared these schemes and discussed open issues.  
Location privacy and differential privacy have also concerned researchers in recent years. The survey [22] analysed proposed location privacy protection schemes for vehicular systems. The authors of [23] discussed location privacy and made a comprehensive review of existing trust models, aiming to protect privacy and security in vehicle cloud computing. In [24], the authors investigated and compared existing local differential privacy techniques and applications for privacy presentation in IoV.  
A comprehensive survey on security with privacy aspects is presented in [25]. The survey does not focus on privacy but extends to various fields of IoV, including blockchain technology. VANET-based authentication schemes are compared in [26]. The authors categorise the schemes into cryptography, signature and verification, and some of the privacy-preservation aspects are discussed.  
In contrast, only one survey investigated blockchain solutions in IoV. The authors of [27] focused on the use and integration of blockchain technology in the Internet of Vehicles. For that reason, they presented and compared existing blockchain solutions for Internet of Vehicles. They also provided an analysis of different requirements of blockchain-based applications in vehicular systems and a presentation of open challenges in this area.  
Although there has been a lot of research on privacy issues in the field of IoV, IoV related systems that use blockchain technology have not been explored with respect to privacy. For that reason, in the present work, we investigate blockchain-based solutions which also aim at maintaining the privacy of the involved parties. In IoV, there are three main privacy concerns: the reveal of user identity, the location exposure and theft or disclosure of data.