Cooperative downloading with privacy preservation and access control for value-added services in VANETs.

Value-added services in Vehicular Ad Hoc Networks VANETs have gained increasing popularity in recent years. However, Road Side Units RSUs cannot usually cover the whole region, resulting in intermittent connectivity. Therefore, how to download data continuously while preserving usersu0027 privacy remains an open problem. In this paper, we propose an efficient data downloading scheme based on usersu0027 cooperation, providing continuous downloading services even when the region is not completely covered by RSUs. Moreover, in order to protect data receiversu0027 privacy and realise fine-grained access control, we employ Ciphertext Policy Attribute Based Encryption with Constant Length CP-ABE-CL with consideration of usersu0027 charge levels. The security analysis shows that our scheme can achieve mutual authentication for vehicles and RSUs, and realise fine-grained access control while preserving privacy of data receiversu0027 identities. The performance analysis demonstrates that our scheme is efficient enough to be implemented in VANETs.