Efficient Anonymous Authentication and Key Management Techniques for Vehicular Ad-hoc Networks

The Vehicular ad-hoc network (VANET) is an important communication paradigm in modern-day transport systems for exchanging live messages regarding traffic congestion, weather conditions, road conditions, and targeted location-based advertisements to improve the driving comfort. In such environments, authentication and privacy are two important challenges that need to be addressed. There are many existing works to provide authentication and privacy in VANETs. However, most of the existing authentication schemes are suffering from high computational cost during authentication and high communication cost during secure key distribution to a group of vehicles. Moreover, in many existing schemes, there is no conditional tracking mechanism available to revoke the misbehaving vehicles from the VANET system. In order to overcome these issues, four new approaches have been developed in this research work: Firstly, a dual authentication scheme is developed to provide a high level of security on the vehicle side to effectively prevent the unauthorized vehicles entering into the VANET. Moreover, a dual group key management scheme is developed to efficiently distribute a group key to a group of users and to update such group keys during the users' join and leave operations. Secondly, in order to preserve the privacy of vehicle users, a computationally efficient privacy preserving anonymous authentication scheme (CPAV) is developed to anonymously authenticate the vehicle users based on the use of anonymous certificates and signatures. Moreover, a conditional tracking mechanism is introduced to trace the real identity of vehicles and revoke them from VANET in the case of dispute. Thirdly, an efficient anonymous authentication scheme to preserve the privacy of RSUs is proposed in this research work: Each authenticated vehicle is required to authenticate the RSUs in an anonymous manner before communicating with it because each RSU provides the location based safety information (LBSI) to all authenticated vehicles when they are entering its region. By doing this, each RSU provides the knowledge to vehicle users about the obstacles within its coverage area. Finally, a computationally efficient group key distribution (CEKD) scheme for secure group communication is proposed in this research work based on bilinear pairing.

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Chapter 4.5 PERFORMANCE ANALYSIS:
The proposed research work is analysed in terms of two performance metrics namely the computation time and communication time for updating the group key in order to perform secure group communication in the PUs of VANET communication. The computation time is defined as the time taken to compute group key at the TA when group membership changes in the VANET group. The communication time is defined as the time taken to broadcast the amount of information from TA in order to make the VANET users to recover the group key. Table 4.1 shows the computation and storage complexities of various key management approaches, namely Chinese Remainder Group Key (CRGK) (Zheng et al. 2007), Fast-chinese Remainder Group Key (FRGK) (Syamsuddin et al. 2008), Key-tree Chinese Remainder Theorem (KCRT) (Zhou & Ou 2009), Number Theory Research Unit (NTRU) (Lv et al. 2012) and Elgamal Group Key Management (EGKM) (Lv et al. 2012) and the proposed VANET Group Key Management (VGKM) which are based on the CRT. The notations used for comparisons are defined as: n is the number of users, is the maximum number of children of each node of the tree, EEA is the time taken to find the inverse element of a multiplicative group using Extended Euclidean Algorithm, exp represtens the exponential operation, M represents the multiplication operation, D represents the division operation, A represents the addition operation and S represents the subtraction operation.
Among these schemes, the Number Theory Research Unit (NTRU) based group key management scheme uses a multiplication ring from which it chooses some polynomial values as private and public keys from which it computes a common group key. Hence, the multiplication operation used in this scheme is performed by using the convolution product method. All the remaining schemes use a multiplicative group for choosing and computing the keys. Moreover, all the existing schemes take O(n) for updating the group key when a single AV user joins or leaves from the secure VANET communication. From Table 4.1, it is evident that all the existing approaches take more computation complexity if it is used in the TA side in the VANET for computing the group key for performing a single user join/leave operation which is very high in comparison with the proposed approach. Therefore, the proposed approach takes less computation complexity when it is compared with all the remaining five approaches since it takes only 1 subtraction operation or (addition) operation to be performed when a single user leave or join operation is performed. Moreover, the proposed approach doesn't perform any cyclic convolution product operation and multiplicative inverse operation on the user side which reduces user's computational complexity. The amount of information bits necessary to be communicated while updating the group key to our proposed approach and existing approaches are calculated and are also shown in Table 4.1. It is very clear that the proposed group key management scheme takes the same communication complexity as that of most of the existing group key management protocol which are based on CRT [...].
The graphical results shown in Figure 4.3 are used to compare the group key computation time of TA for the proposed method with the existing methods. It compares the results obtained from the proposed VGKM with CRGK, FRGK, KCRT, NTRU and EGKM. From Figure 4.3, it is observed that when the key is 512 bits, the group key computation time of TA is found to be 19ms in the proposed approach, which is better in comparison with the other existing schemes. The results shown in Figure 4.4 are used to compare the PUs key recovery time of the proposed method with the existing methods. It compares the results obtained from the proposed scheme with existing approaches and it is observed that when the key size is 512 bits, the key recovery time of a user is found to be 5.3ms in the proposed approach, whic