## 2 ITS Security and Privacy Challenges  
In ITS, security and privacy are the most ambitious problems and privacy should be examined along with security [27]. Every member of ITS should be authenticated. Similarly, every beacon should be verified to reduce the risk of security and privacy attacks in ITS. ITS-S (vehicle) privacy ensures the protection of the ITS user location and real identity. Security and privacy needs are satisfied through fictitious identities [29]. The nature of ITS is that it is wireless, with high speed mobility, dynamic topology, sparse and dense scenarios and is susceptible to attacks when segregating with other ICT based networks. In ITS, vehicles broadcast messages to inform other vehicles about the traffic situations, however, malicious vehicles might broadcast bogus messages or alter the original messages of a legitimate ITS user. The aim of ITS cannot be achieved and honest ITS users can be misguided. An adversary can misguide or eavesdrop honest ITS user's data for his/her personal interest. Therefore, there should be proper mechanisms to ensure the authenticity and integrity of messages [31]. If an ITS-S (vehicle) is found guilty, it should be revoked from ITS. There should be proper security and privacy approaches for registration and revocation of vehicles. [PERSON] et al. [32], discussed the issue of scrambler attacks on location privacy of vehicles/drivers. Usage of predictable scramblers cannot protect location privacy of vehicles. The scrambler (change signals) component of all IEEE 802.11p and Wi-Fi radio transceivers cannot guarantee the performance at the lower physical layer and needs to improve the performance of wireless communication. There is also a need to incorporate strong cryptographic techniques. [PERSON] et al. [33] proposed a scheme to protect user privacy in which a user, as well as authority, cannot track a vehicle. However, the mechanism is not at par with ITS system because there is no consideration for revocation and accountability of malicious vehicles. Security and privacy issues are mainly categorized as features, attacks, and challenges as shown in Figure 5. These issues are given in detail as follows:  
* Confidentiality: This feature ensures that only authorized ITS users have access to data. The data cannot be snooped or hindered by unauthorized users. Confidentiality is an important service in ITS, during the pseudonym registration and obtaining phases. Thus, it is important to ensure confidentiality of ITS. Therefore, advanced cryptographic techniques should be considered [34]. * Integrity: Integrity can assure the exact delivery of messages. In ITS integrity is important, because wrong or tampered messages can misguide honest ITS users. Integrity avoids expected or unexpected intervention during the communication. In order to achieve fair integrity in ITS, strong security mechanisms should be designed [35]. * Availability: This feature in ITS guarantees that the servers and data are always available to authorize ITS users. In ITS, services are needed in real time. Therefore, the availability feature should be considered. [PERSON] al. [36] discussed that denial of service attack is the most dangerous threat for the availability of services in ITS. In order to ensure availability, enhanced security approaches should be considered in ITS. * Identification: This feature can ensure that unauthorized ITS-S (vehicles) cannot be linked in ITS. Identification of each ITS-S is difficult. Therefore, there is a need to design and develop effective mechanisms for the identification of vehicles [37]. * Authentication: Authentication can ensure that the messages received are legitimate. However, authentication can be carried out in ITS without revealing the real identity of the vehicle. Efficient approaches are needed to deal with this feature [37]. * Non-Repudiation: This feature ensures that the communicating entities cannot deny the previous communication. In order to avoid malicious threats in ITS, a non-repudiation feature must be considered.