CACPPA: A Cloud-Assisted Conditional Privacy Preserving Authentication Protocol for VANET

Vehicular ad hoc network (VANET) is an application of intelligent transportation system (ITS) with emphasis on improving traffic safety as well as efficiency. VANET can be thought as a subset of mobile ad hoc network (MANET) where vehicles form a network by communicating with each other (V2V) or with infrastructure (V2I). Vehicles broadcast not only traffic messages but also safety critical messages such as electronic emergency braking light (EEBL). A misuse of this application may result in a traffic accident and loss of life at worse. This situation makes vehicles' authentication a necessary requirement in VANET. During authentication, vehicle's privacy related data such as vehicle and owner's identity and location information should be kept private in order to prevent an attacker from stealing this information. This paper presents a cloud-assisted conditional privacy preserving authentication (CACPPA) protocol for VANET. CACPPA is a hybrid approach that utilizes both the concept of pseudonym-based approaches and group-signaturebased approaches but cleverly avoids the inherent drawbacks of these approaches. CACPPA neither requires a vehicle to manage a certificate revocation list nor does it require vehicle to manage any groups. In fact an efficient cloud-based certification authority is used to assist vehicles getting credentials and subsequently using them during authentication. CACPPA provides conditional anonymity that a vehicle's anonymity preserved only until it honestly follows the protocol. Furthermore, we analyze CACPPA with various attack scenarios, present a computational and communication cost analysis as well as comparison with existing approaches to show its feasibility and robustness.