ItAU: Incentive and Traceable Authentication for VANET via Weighted Threshold Signature

Vehicular Ad-hoc Network (VANET) widely applies digital signature to guarantee data integrity. Centralized holding of the signing key incurs the single-point failure problem, and further information faking and unauthorized access. Existing technologies such as threshold signature can be used here to decentralize the trust of traffic data from the single vehicle to multiple vehicles, however, the complicated collection and the count-based judgment inhibit the traffic data utilization. In this paper, we introduce an incentive and traceable authentication (itAU) framework for VANET. It utilizes the threshold setting to ensure the reliability of traffic data and employs the incentive mechanism to solve the complicated data collection. Vehicle weights are adjusted based on historical performance, and traceability is restricted on the cloud server to protect vehicle privacy. To instantiate itAU, we propose a cryptographic primitive named weighted threshold signature with private accountability (WTAPS), which computes the weighted sum of signers for threshold judgment and enables private tracing through the generation of a tracing secret key. WTAPS is formally proven to be unforgeable and accountable under the decisional Diffie-Hellman (DDH) assumption via game-hopping. We present a concrete itAU design from WTAPS, where WTAPS supports the signature generation of vehicles, the signature combination of the RSU, and the signature verification and vehicle traceability of the cloud server. A reputation-based incentive mechanism is embedded to encourage the active participation of vehicles and provide standards for weight settings. Experimental results show that itAU is cost-reasonable that the running of the entire process is less than 2 s with the configuration of 100 signers.