# Blockchain-Based Authentication in Internet of Vehicles: A Survey
## 3 Security Issues in IoV and VANETs
### Security Requirements and Challenges in Vehicular Networks
Data verification: Since malicious entities can modify the information sent by the sender, a regular data verification process is usually performed to identify the manipulated or tampered messages and thus reject or drop them (if found) to prevent misleading the receiving entities into taking improper decisions. 9. Real-time guarantee and efficient routing: The majority of IoV and VANETs applications are real-time, such as accidents detection and warnings dissemination, which must be carried out within certain time constraints, otherwise the safety of drivers and passengers could be threatened, and the delayed information will become worthless. To be able to meet these time constraints, efficient secure routing protocols should be adopted to guarantee delivering the packets in their entirety and on time. 10. Traceability and revocability: Despite the need for preserving the privacy of IoV users in general by hiding their real identities, the legal authorities should have the ability to retrieve the vehicles' real identities in case of misbehaving to revoke them as well as in case of disputes. 11. Scalability: With the increasing number of vehicles on the roads nowadays, more vehicles and entities are joining the network. Thus, a good vehicular network should be able to scale-up accordingly. However, this nodes extension may expose the network to higher security issues if not controlled and monitored properly. Therefore, monitored scalability is another security requirement of the IoV system. The following are different security challenges that might be faced by any IoV paradigm [89; 92; 93; 94; 95; 96; 97]:  
1. High mobility: Data packets must be preserved and kept unmodified during the entire uncertain routing process from the sender to the receiver and should also be delivered on time to satisfy the real-time security requirement. However, the high mobility of nodes in IoV and VANETs networks, and the continuously varying network topology have led to the transient nature of V2V and V2I interactions, which makes the real-time guarantee and non-repudiation security requirements much more difficult. 2. Low errors tolerance: Any minor delay in receiving information or delivering packets in IoV may result in unacceptable situations or even road disasters, thus the time constraints are of high importance in such environments. However, the limited bandwidth and the unstable network quality in IoV caused by the huge number of vehicles being served, their mobility, and the unpredictable changes in wireless networks hinder the real-time security requirement. Therefore, some preventive security measures must be applied so that the drivers can be proactive in case of any emergency situations. 3. Key management: Several authorities and stakeholders are considered important participants in IoV such as governmental institutions and vehicle manufacturers. Hence, it has always been a security challenge to delegate a certain authority among these stakeholders to serve as a fully Trusted Authority (TA) that is responsible for key distribution, management, and revocation, since choosing the wrong authority  
Figure 3: The security requirements and challenges in IoV and VANETs platforms. without considering its hidden intents and benefits could severely affect the security of the IoV system. Moreover, due to the scale of IoV and VANETs networks, the Certificates Revocation Lists (CRLs) that are responsible for the revocation of misbehaving and malicious vehicles become too long and thus not feasible which raises the overhead of the certificate revocation process. Thus, maintaining a balance between efficient key distribution/revocation process and low overhead is another challenge on IoV security. 4. Tradeoff between security and privacy: In general, the more secure the system is, the less privacy it can provide for users. Many drivers and passengers may not be willing to sacrifice their privacy by sharing their private sensitive data such as their location and destination while caring for security at the same time.