# Blockchain-Based Authentication in Internet of Vehicles: A Survey
## 2 Background
### Motivations to Use Blockchain in IoV  
IoV is a large-scale and heterogenous network that combines a large number of connected vehicles, roadside infrastructure, mobile personal devices, central and distributed storage, and computation servers in case of incorporating cloud and edge computing platforms. This along with the open-channel wireless communication model and the public Internet connectivity that dominate most of the communication makes the IoV network vulnerable to a variety of security attacks that could threaten the applications of IoV such as navigation, accident detection and notification, dynamic alternative routing, route optimization, and congestion management which consequently constitutes a threat and danger on drivers and passengers on the road. Furthermore, since IoV scenarios include high mobility and exchange of huge amount of data as well as requiring real-time services and decision making, more efficient, powerful, and reliable technologies must be adopted in IoV frameworks in place of the conventional techniques.  
On the other hand, blockchain technology has emerged recently as a decentralized storage mechanism in various industry applications due to its strong capabilities not only in distributed storage aspect, but also in terms of security, privacy, performance, automation, and reduced computational cost. Recently, blockchain has also been brought to the IoV paradigm to serve different purposes such as data protection and management, resource trading, resource sharing, ride sharing, traffic control and management, and forensic applications.  
The various features a blockchain can provide have motivated researchers and the industry to incorporate blockchain technology into the IoV. These properties include the following [85; 86]:Decentralization: Unlike the centralized-storage platforms where both data storage and management are handled by a trusted centralized node, blockchain technology exhibits a decentralized nature in which data records are kept and managed by all participating entities. This reduces the resource bottlenecks issue and maintenance cost associated with the centralized sever arrangements and avoids the single point of failure issue which all can be beneficial for IoV environments.
2. Immutability: Since the creation and validation of new blocks of transactions should be agreed upon by all or most of the peers via the different consensus mechanisms before being added to the blockchain, the blockchain is almost impossible to be tampered with or modified.
3. Security and privacy: The cryptographic nature of blockchain where both cryptographic hash functions and digital signatures are adopted can ensure the security of transactions data and the privacy of the participating users in IoV.
4. Transparency: Since all participants keep a replica of the public ledger, they can access all the timestamped blockchain transactions. This enables the peers to manage, look up and verify transactions at any time in a transparent manner without an intermediary. This self-auditability and transparency not only promote the relief of the peers by managing their own transactions, but also mitigates the time and financial costs associated with the intermediate party.
5. Automation: Blockchain technology supports the adoption of smart contracts which are software scripts that can be executed automatically by a triggering event or upon meeting some pre-defined set of rules. This automation property of blockchain can enhance the efficiency of many IoV applications and help provide various services autonomously without a need for a trusted entity.
6. Traceability: Each transaction record is kept in the blockchain with a timestamp indicating its time of occurrence and joining the public ledger. This timestamped recording nature helps identifying the events in a chronological order which enhances the traceability and can support the non-repudiation requirement in IoV.