# An Enhanced Privacy-Preserving Authentication Scheme for Vehicle Sensor Networks
## 1 Introduction  
With the rapid development of the intelligent transportation systems (ITSs) [1], vehicular ad hoc networks (VANETs) have become increasingly popular. The vehicles in VANETs can communicate with each other via wireless communication [2]. If vehicles can interact with other vehicles or the roadside infrastructure to exchange collected data for decision-making and safer driving, traffic jams can be avoided and the safety of drivers can be guaranteed to the utmost extent; consequently, VANETs are a promising means of improving traffic safety and management. At present, vehicles are equipped with various sensors that can provide valuable data. Further equipping vehicles with onboard sensing devices can turn VANETs into vehicle sensor networks (VSNs) [3]. Therefore, the authentication protocols used in VANETs can also be used in VSNs. Moreover, dynamic traffic information and many types of physical data associated with traffic distributions can be sensed and collected by such vehicular communication networks. Therefore, VSNs are expected to significantly facilitate future wireless communication.  
Two types of communication exist in VANETs, namely vehicle-to-vehicle (V2V) communication and vehicle-to-infrastructure (V2I) communication, which depend on two essential kinds ofcomponents: onboard units (OBUs) and roadside units (RSUs). As shown in Figure 1, OBUs are the wireless communication units equipped on vehicles, whereas RSUs are wireless access units located at significant places on the road. Generally, to assist vehicles and RSUs in performing certain tasks, such as authentication, a backend server should be deployed remotely. The characteristics of VANETs include self-organization, channel-opening behavior, and rapidly changing and multiple-hop topologies. Due to these characteristics, VANETs are more susceptible to malicious attacks. Since safety and privacy are a concern in many applications in VANETs [4; 5], communication security issues are worthy of attention. Among the various security mechanisms used in VANETs, authentication is one basic component that is critical for ensuring security. However, a desirable authentication scheme must be efficient and practical for use in fast-moving scenarios, which means that the computation cost for authentication should be as low as possible to enable real-time response. In addition, privacy preservation should be considered, including the identity privacy, location privacy, and interest privacy. Moreover, the location of a vehicle is closely related to who is driving it. When a vehicle communicates with others in a wireless network, it will not be acceptable to the public if the vehicle's identity and location are disclosed. Thus, privacy preservation must be achieved in the authentication procedure. In addition, it should be possible for the real identities of the malicious vehicles to be revealed by the authorities when necessary [5]. These requirements pose a considerable challenge for the development of an ideal authentication scheme.  
The contributions of this paper are as follows: (1) an enhanced privacy-preserving authentication scheme based on the [PERSON]'s scheme is proposed that can resist internal attack. In addition, we demonstrate the correctness and security of the improved scheme and analyze its computational costs; (2) to preserve the identity privacy of drivers, anonymity is achieved by randomizing the real identities; and (3) to preserve the location privacy of drivers, unlinkability is achieved in the authentication procedure.  
The remainder of this paper is organized as follows. Related work is introduced in Section 2. Preliminaries are presented in Section 3. A review of the [PERSON]'s scheme is provided in Section 4. Then, a concrete description of the proposed scheme is offered in Section 5. Section 6 presents the proofs of correctness, security and performance. Finally, the conclusions are provided.  
Figure 1: Structure of a vehicular ad-hoc network.