Abstract
Vehicular Ad Hoc Networks (VANETs) play a critical role in Intelligent Transportation Systems (ITSs), enabling secure communication between vehicles and roadside infrastructure. However, in dense traffic environments, conventional centralized Vehicle-to-Infrastructure (V2I) authentication schemes impose a significant computational burden on Roadside Units (RSUs), leading to authentication delays and degraded service quality. To address this challenge, we propose a cooperative V2I authentication protocol that delegates part of the computational workload to nearby trusted vehicles. A novel dual-verification mechanism, based on asymmetric delegation and a concealed perturbation point, ensures correctness even in the presence of misbehaving or colluding helpers. This structure differs from previous cooperative authentication models by introducing redundancy and verifiability into offloaded computations. In contrast to prior RSU-centric or fog-layer solutions, our protocol distributes workload without compromising security guarantees. The proposed scheme supports batch authentication and group session key establishment, enabling efficient and scalable secure communication for both V2I and V2V scenarios. Moreover, it incorporates dynamic pseudonym updates and flexible certificate revocation, achieving strong privacy protection with conditional traceability. Formal security analysis under the Real-Or-Random (ROR) model demonstrates robustness against impersonation, replay, and tampering attacks. Simulation results confirm that our protocol reduces RSU-side computation overhead by over 20% under comparable conditions, offering a lightweight and practical solution for real-time authentication in dynamic vehicular networks.