# Blockchain-Based Authentication in Internet of Vehicles: A Survey
## 3 Security Issues in IoV and VANETs
### Security Requirements and Challenges in Vehicular Networks  
The IoV networks are an amalgamation of diverse technologies with different standards and regulations (such as Internet connections, different wireless technologies, sensors, cloud services); which make IoV vulnerable to various types of security attacks. Depending upon the attacker objective(s), the attack launched might be passive or active, generated internally or from an external source. However, regardless of the attack's source or activity type, these security threats are commonly classified into different categories based on the security aspect(s) of the network being compromised. For example, an attack could affect the authenticity of the users, the integrity of IoV data, or the availability of the provided services. Guided by the various security threats an IoV system can suffer from, different security aspects have been defined in the literature. These security aspects can be classified into: (1) Security requirements that an efficient IoV system should maintain and (2) Securitychallenges that face any security subsystem of an IoV environment. Figure 3 illustrates these security requirements and challenges. Following are the different security requirements of an IoV system [87; 88; 89; 90; 91]:  
1. Authentication: It means ensuring that the received data is generated by a legitimate sender, or in other words, making sure that the entity that sent the data must be the true actual entity it claims to be. It guarantees that the entities involved in the communication are authentic, not masqueraded by some attacker who forwards the messages on their behalf. Sybil attack, masquerading attack, impersonation attack, spoofing attack, replay attack, and wormhole attacks are examples of attacks that target the authenticity of IoV users. 2. Availability: It is a basic requirement in IoV environment especially for the real-time critical applications where even a minor delay cannot be tolerated and made the information useless. Therefore, the IoV system should be available all the time to provide real-time information and services to all legitimate users and be able to tolerate partial system faults and failure issues through backups and replications. Moreover, a mature IoV system must have the ability to function under intense network load with the increasing number of participants. The common attacks that target the availability service are the denial-of-service and distributed denial-of-service attacks. 3. Confidentiality: Some IoV applications include sensitive information that are accessed only by certain legitimate users. Therefore, confidentiality of this information must be insured through encryption to prevent it from being revealed and interpreted by any illegal entity even upon eavesdropping. 4. Data integrity: It means there is no distortion--whether intentionally or accidentally--in the received data. In other words, the sent data and the received data are identical. Typical attacks on integrity can be data manipulation attack and malware attack. 5. Non-repudiation: It guarantees that any involved user in the IoV environment cannot deny any of its past activities, i.e., sending or receiving any piece of information. This ensures that an attacker can be identified, and all its communicated messages can be retrieved if needed for subsequent actions. 6. Access control: Each participating entity in the IoV network is assigned different rights and privileges to access the network resources. This security requirement guarantees that each node performs its functions based on the services it is entitled to. 7. Privacy and anonymity: The users' real identities may need to be made hidden using anonymous identities or pseudonyms to protect their privacy. Additionally, some location information such as the driving traces and tracks followed by the vehicles are sometimes preferred to be anonymous in order to prevent unauthorized location tracking. 8.