## 1 Introduction
* Decentralization: Due to the ad hoc nature of ITS, there is no fixed central system that ensures trustworthy communication of vehicles. As different vehicles are joining and leaving the VANET [5]. There is a need to focus on the designing of trustworthy security approaches to work reliably under decentralized scenario. * Malicious attackers: Due to the wireless and ad hoc nature of ITS, attackers try to inject bogus beacons or alter the attacked beacons [24]. The attacker tries to misguide honest vehicles for their personal interest. In ITS, a lot of research work is done to consider security and privacy issues. [PERSON] et al. [25] discussed the security susceptibility and threats in ITS. There are security and privacy-related challenges from the perspective of applications, network and technologies. [PERSON] et al. [26] discussed only the issues of integrity and access control but did not elaborate the various security and privacy mechanisms. [PERSON] et al. [27] present a survey on the security and privacy issues of ITS, but it lacks proper analysis of the security and privacy approaches. Similarly, [PERSON] et al. [24] present a survey and discuss security and privacy approaches but it lacks proper analysis for different types of attacks on ITS communication layers, scalability, and computational cost. [PERSON] et al. [28] specified security and privacy requirements in ITS but do not properly analyze the security and privacy techniques for ITS suitability. [PERSON] et al. [29] provide an excellent survey on pseudonyms schemes in ITS but consider only limited types of attacks. There is a lack of the individual technique proper analysis in each group. Similarly, a survey presented in [30] is an excellent survey on pseudonym changing mechanisms to protect location privacy but lacks analysis of each technique in every privacy category of ITS with respect to latency, computational cost, communication overhead, and different types of attacks as discussed in Section 2 of this paper. A number of surveys have been conducted for the security and privacy challenges in ITS. However, still there is a need to present an extensive survey of ITS security and privacy to assist researchers in the emerging area of ITS. This paper discusses the security and privacy challenges in ITS and provides analysis of security and privacy approaches in terms of different types of attacks on ITS communication layers, scalability, computational cost, communication overhead, and latency. The contributions of this paper are:  
* The ITS security and privacy challenges are reviewed and presented. * Different types of security and privacy attacks in ITS are analyzed and discussed. * Privacy schemes in ITS are examined and categorized based on scalability, latency, computational cost, communication overhead, security, and privacy attacks. * New research challenges in ITS security and privacy are presented. * A discussion towards the integration of ITS in the cloud is presented. The rest of this paper is organized as follows: Section 2 consists of ITS security and privacy challenges. Section 3 consists of the categorization of privacy mechanisms in ITS. Section 4 presents the group/ring signature-based schemes. Section 5 consists of the pseudonym-based approaches. Section 6 presents hybrid schemes. Section 7 discusses the integration of ITS in the cloud. While Section 8 presents a conclusion and future direction.