## 2 ITS Security and Privacy Challenges
* Privacy: A privacy feature in ITS can guarantee that only the authorized servers can control the anonymity. Confidentiality aims to encrypt the data, while privacy ensures that the real identity of information cannot be revealed from messages/data [38; 39; 40; 41]. In ITS, privacy of a legitimate vehicle is the most important attribute. In order to avoid tractability of an honest ITS user, there is a great need for the design and development of security and privacy mechanisms. * Trust: Trust can guarantee the preceding security and anonymous communication features to be accomplished during the give and take phases among distinct entities. In ITS, the feature of trust can be divided between applications and entities [25]. In order to achieve trust in ITS, there is a need to develop trustworthy approaches. According to the ETSI, the communication architecture of an ITS-S consists of an access layer, networking and transport layer, and facilities layer [8]. In ITS, the facilities layer is constituted via obtaining the performance of data usages in the network and transport layer. In the facilities layer, security provocation can be judged by the provocation in the access and networking and transport layers. 1. Access layer: The main objective of an access layer in ITS is to transmit and receive messages. The security challenges in this layer are: 1. Node capture attack: In this type of attack, an opponent can get and hold the node i.e., ITS-S (vehicle or RSU) in ITS via medtling with the OBU of the vehicle [42]. If an ITS-S (vehicle or RSU) is paced by the node capture attack, the key information can be exhibited to the opponent. The attacker can easily copy the key information of the attacked node/ITS-S. In this way, the malicious vehicle can easily become an authorized vehicle to connect into the ITS. The node capture attack is considered as the node replication attack. In order to prevent the node capture attack, capable security and privacy approaches are needed [43]. Figure 5: ITS security and privacy issues. * Malicious code injection attacks: The malicious code injection attacks [44], can easily grant permission of an opponent into ITS. In order to preserve from malicious code injection attacks, the designing of capable code authentication approaches is required [44; 45]. * False data injection attacks: [PERSON] et al. [35], discussed that with node captured attack, the opponent can easily insert the wrong information. In this way, the receiving vehicles are misguided, which affects the ITS. In order to identify false data, proper security schemes need to be designed [46]. * Replay attacks: Replay attacks are also called freshness attacks [47; 48], in this type of attack, an opponent can use an attached ITS-S to send messages with legal evidence. Authentication processes are commonly affected through replay attacks. To overcome the replay attack effect, proper time stamp approaches must be developed in ITS [49]. * Cryptanalysis and side-channel attacks: In this type of attack, an eavesdropper tries to get key information from the obtained cipher text [50]. However, if strong security and privacy techniques are used, the chances of cryptanalysis attack are less. Similarly, the opponent can launch aside-channel attack, the opponent can use some mechanisms on the devices (e.g., RSUs) in ITS and try to get the cipher key information. In order to relieve the side-channel attacks, effective security and key management approaches are required in ITS [34]. * Interference and eavesdropping: As the nature of ITS is wireless, if there are no security measures the communication can be monitored easily by unauthorized parties [42; 51]. To relieve ITS from eavesdropping, proper security approaches are needed. Noise data can be sent by the adversary to impede with the distributed information in wireless communication. In order to guarantee the timely and accurate delivery of information in ITS, effective security and privacy approaches are needed to avoid the interference by unauthorized users [52].