Vehicular ad hoc networks (VANETs) face two important and conflicting challenges with regards to security: preserve the privacy of vehicles in order to prevent malicious entities from tracking users and detect and remove bad actors that attempt to game the system for their own advantage. In particular, detecting Sybil attacks, in which one node attempts to appear as many, seemingly conflicts with the goal of privacy preservation, and existing schemes fail on either one or both accounts. To fill this gap, we present a hierarchical key management system which uses short group signatures to preserve member privacy at lower levels while allowing mid-level nodes to detect Sybil attacks and highly trusted nodes at the top of the hierarchy to completely reveal the real identities of malicious nodes in order to prevent them from rejoining the system and for use by legal authorities. In addition, we present an argument for relaxing the requirement of backward secrecy in VANET groups in the case when no malicious activity has been detected.

Vehicular Ad hoc Networks (VANETs) are a subset of the Internet of Things (IoT) that are used in smart traffic applications. Due to their high speed, mobility, and exposure to the environment, the security requirements for VANETs result in the conflicting design goals of protecting member privacy while also ensuring non-repudiation. Group signature schemes can fulfill these requirements, but often at the cost of expensive bilinear pairing operations. Furthermore, the cost of updating the group key information can be costly. Accordingly, this paper has two goals. First, it presents a group signature scheme that has been modified to remove pairing operations by caching computed values, while still preserving the critical requirement of conditional privacy. Second, this paper presents an argument for the abandonment of perfect forward and backward secrecy in VANET schemes in order to prevent the generation of keys that are never used, or used only once, and reduce the twin burdens of excessive key recalculation and key redistribution on the system.

Vehicular Ad-hoc Networks (VANETs) are a type of Internet of Things system where groups of vehicles communicate with each other and traffic monitoring infrastructure in order to provide safety and quality of life improvements for drivers and others in the area. Vehicles in a VANET are responsible for reporting their own status, as well as the statuses of the roadway, traffic, and environment in their immediate vicinity, to the system controller and other drivers for processing. VANET systems are open to the public, with vehicles joining and leaving at a high rate. This feature results in two high-priority requirements for VANET security: vehicles in a VANET must be held responsible for the correctness of the information that they report, and schemes ensuring message security must be quick. This paper presents an efficient, pairingfree signature scheme for VANETs that prevents the forgery of signer identities, including in the case of insider attacks, without the use of a tamper-proof device.