A Secure Official Vehicle Communication Protocol for VANET Xia-Yun Guo Department of Computer Shenyang Aerospace University, Shenyang, Liaoning 110136, PRC 15035297641@163.com Chin-Ling Chen Department of Computer Science and Information Engineering Chaoyang University of Technology, Taichung, Taiwan, clc@mail.cyut.edu.tw Chang-Qing Gong Department of Computer Shenyang Aerospace University, Shenyang, Liaoning 110136, PRC gongchangqing@sau.edu.cn Fang-Yie Leu Department of Computer Science Tunghai University Taichung,40704, Taiwan, leufy@thu.edu.tw Abstract—Vehicular ad hoc network (VANET) has been a hot topic in recent years. Currently, VANET research mainly focuses on enhancing road safety, traffic safety warning, and reducing traffic accidents. In the future, the security of vehicle communication ought to be considered to protect privacy of users, such as personal ID and vehicular route. In order to enhance public service vehicles management, ensure official activities, and reduce finance expenditure meanwhile, a secure official vehicle communication protocol for VANET is proposed in this paper. The proposal combines homomorphic key agreement, symmetric encryption, message authentication and digital signature mechanism, etc. Based on the protocol, personal information of users can be better protected. Besides, the proposed scheme has properties of mutual authentication anonymous, availability, non-repudiation and security, all of which are beneficial to privacy protection. Keywords- VANET, MAC, digital signature I. INTRODUCTION Vehicular ad hoc Network, VANET has its own unique characteristics for traditional mobile ad-hoc network. VANET with high dynamic topology, enough energy and storage space, moving track predictable and diversified automotive network scenarios, has many significant applications in transportation and communication, such as vehicle safety, road traffic efficiency, and information and entertainment. [1]. Li et al.[2] proposed a secure and efficient vehicle network communications scheme using asymmetric encryption to build authentication keys and protect privacy. In addition, Li et al.[3] also combined asymmetric encryption and hash functions to improve security of their scheme. However, the computational cost is still too high. In order to satisfy the requirement of wireless network security, International Society of Electrical Engineering Electronics upgrades IEEE802.11 wireless communication standard to IEEE802.11p [4], a wireless access in the Vehicular Environment, WAVE, for vehicle communication. But the IEEE 802.11p standard has not been applied in large-scale application. This paper is on the basis of VAiPho [5] secure communication systems, as well as smartphones which are equipped with a Global Position System (GPS) and Wi-Fi connection. Firstly, we propose a vehicle network security communication protocol about official vehicles. In emergency, official vehicles can request for the public key processed to the service node. After receiving the request, the service node first verifies identity of the official vehicles, and then sends the public key of the key management server to the official vehicles. Official vehicle and key management agencies generated the session key through homomorphic key agreement mechanisms, and reduced the computational costs. Secondly, we propose a secure official vehicle communication protocol for VANET, protect the communication transmission, and satisfy the security requirements. II. PROPOSED SCHEME A. Roles and Procedures In this section, we describe our proposed Security protocol in detail. (1) Key Management Server (KMS) is in charge of all system parameters and keys. (2) Road-side Transportation Authority (RTA) is an entity that receives event information and distributes official vehicles. (3) Official Vehicles (OV) represent the official activity vehicles in service. (4) Civil Servant (CS i ) is an official activities executor. (5) Service Point (SP) is responsible for authenticating CS i . Then the CS i gets access the Internet resources via SP, and obtains the services which are supported by the KMS. B. Notations X ID X  s identity Y X SK  session key between by X and Y X S X  s digital signature X P X  s pseudo identity X K X  s session key i M ith communication message T  the valid time length p , q secure primes p and q i C ith ciphertext Y X ?  verify whether X is equal to Y Y X ?  determine whether X is less than or equal to Y i MAC ith message authentication code   h the one-way hash function ） （ i Puk M V X verify message M i with X’s public key X Puk   i M S X k Pr sign message M i with X’s private key X k Pr   i SK M E Y X  encrypt message M i with symmetric key Y X SK    i M D Y X SK  decrypt message M i with symmetric key Y X SK  i T ith timestamp