Focusing on the problem that the privacy-preserving of identity authentication in Vehicular Ad Hoc NETworks (VANET), a conditional privacy-preserving authentication scheme was proposed. Firstly, this paper introduced the short signature technology, and then constructed a new identity-based short signature scheme. Compared with the well-known Conditional Privacy-Preserving Authentication Scheme (CPAS), the proposed scheme could reduce the computation costs required for both signature and verification processes and improve the communication efficiency. Secondly, the scheme divided the private signature key into two correlative sub-segments, so that it could effectively solve the issue of key escrow. Therefore, the scheme was especially suitable for the environment of VANET. Based on the proposed signature scheme, a conditional privacy-preserving authentication scheme was presented, which can achieve identity authentication with conditional privacy preservation. The theoretical and efficiency analysis shows that the scheme needs only three dot multiplication in the signature process and takes one dot multiplication, two pairing operation in the verification process. Especially, the proposed scheme use batch verification by adding the small coefficient test to accelerate the authentication speed and reduce the error rate.

Concerning to the problem of preserving users' identity privacy during the process of authentication in Vehicular Ad Hoc NETwork (VANET), a novel anonymous authentication scheme without cryptography based on the theory of linear equation was proposed. The scheme constructed an anonymous authentication model based on the basic theory of solving linear equations without employing any symmetric or asymmetric cryptosystem, which avoided disclosure of the identity information during the process of anonymous authentication. Besides, the proposed scheme not only satisfied the requirement of anonymous authentication between On Board Unit (OBU) and Road Side Unit (RSU), but also ensured the anonymous authentication among OBU. The results of the security and complexity analysis show that the proposed scheme is secure and efficient, and it needs low costs of computation and communication.

A new data sharing scheme was proposed to solve the problem of error-tolerant search and fine-grained access control. This new scheme adopted the technology of locality-sensitive hashing and the predicate encryption, which allowed users to search for keywords in an error-tolerant manner, and modified the users access rights easily by updating the encrypted data. The computational complexity of updating is more optimized than the existing scheme. The theoretical analysis shows that the proposed solution is correct, safe and effective.