# Blockchain-Based Authentication in Internet of Vehicles: A Survey
## 6 Future Research Directions and Open Challenges
### Employing Blockchain for other IoV Security Requirements  
In this survey paper, we targeted the adoption of blockchain in IoV for the authentication security requirement. However, we believe that blockchain can be of great benefits for other IoV security requirements such as data integrity, secure routing, and availability which can all be explored and discussed as part of the future research directions.  
1. Data Integrity: Blockchain can be adopted by IoV environments to ensure that the data sent and received between two communicating IoV entities are identical. In other words, to make sure that no unauthorized modifications on the data take place during transmission. For instance, when a sender aims to send some data to another IoV node, it can send a copy of the data to the publicly accessible blockchain as well. At the other end, when the receiving entity receives the data, it can compare it with the copy stored in the immutable blockchain, if matched that means no manipulation was performed and data integrity is guaranteed. Otherwise, the received data cannot be trusted. The use of blockchains for ensuring data integrity in IoV may become even more important to explore when considering using them for big data analytics and data mining which require the data to have high level of accuracy to result in developing accurate and efficient decision making and AI-based applications.
2. Secure Routing: Blockchain technology can be used for guaranteeing a secure routing in IoV environments via different arrangements. An example could be maintaining a list of all possible legal next-hop nodes in the public ledger which can be accessed by all IoV entities. This list should be firstly developed by gradually adding the ids of the nodes that were successfully registered and authorized by the network. This means that any malicious unauthorized node will not be valid in this routing list. In this way, when an entity receives a packet that was routed through at least one illegal forwarder that does not exist in the routing list kept in the blockchain, this means the routing processes have been compromised and some illegal entity had access to the transmitted packet.
3. Availability: A feasible suggestion that could be investigated is the integration of blockchain with some physical identification modules in an attempt to prevent some availability attacks and threats. That is, obligating each single service request to include the physical identity of the request originator, e.g., MAC address of the NIC of the user's mobile device or the vehicle's hardware id assigned by the vehicle manufacturer. Then, upon receiving the request by an infrastructure node, i.e., a RSU, it should extract the physical identity of the requester and store it as a record in the blockchain while keeping track of a counter that counts the number of successive requests and a timer to monitor the time intervals between these successive requests. In such arrangement, availability attacks specifically the denial of service (DoS) attack that originates from a single physical entity with different logical identities, i.e., IP addresses, can be efficiently detected and thus blocked by any IoV entity through monitoring the public ledger records and noticing any extraordinary behavior of rapid successive requests originated from the same physical id.  
The above-mentioned examples are a few humble suggestions for using blockchain in the context of the different IoV security requirements. However, there is a strong belief that blockchain capabilities can cover more aspects and offer a variety of solutions regarding these IoV security concerns, yet to be explored.