S-PKAD: Secure and privacy-preserving key agreement for low-altitude intelligent transportation systems

Low-altitude intelligent transportation systems (LITS) are increasingly using drones/UAVs in low-altitude airspace to support time-critical services such as last-mile delivery, surveillance, and emergency response. However, open wireless connectivity, high mobility, and lightweight airborne platforms also expose LITS to security and privacy risks, particularly during real-time data access. To address these issues, this paper proposes S-PKAD, a secure and privacy-preserving key agreement protocol tailored to drone-assisted LITS environments. S-PKAD combines ASCON-128 authenticated encryption with elliptic curve cryptography, together with lightweight hash and XOR operations, to provide strong protection with low overhead. The protocol achieves mutual authentication and perfect forward secrecy, preserves privacy, and removes any dependence on clock synchronization. A comprehensive security evaluation, including a formal proof in the Real-or-Random (ROR) model and automated verification using AVISPA, confirms that S-PKAD satisfies key security and privacy requirements for LITS/IoD deployments. Performance and comparative results further show that S-PKAD remains efficient and competitive with recent state-of-the-art schemes.