A Security-Enhanced Certificateless Authentication and Key Agreement Protocol Using Pseudonyms for VANETs

Authentication and Key Agreement (AKA) protocols in Vehicular Ad Hoc Networks (VANETs) play a critical role in ensuring secure and privacy-preserving communications. However, existing schemes still suffer from limitations in practicality, security, and conditional privacy preservation. Specifically, many protocols rely on secure channels during the registration phase, which restricts practical deployment; they fail to provide effective guarantees of perfect forward secrecy and resistance to Key Compromise Impersonation (KCI) attacks under key leakage scenarios; and they struggle to achieve a balance between anonymity and traceability. To address these issues, this paper proposes a certificateless anonymous authentication and key agreement protocol tailored for VANETs environments. The proposed protocol supports secure registration and key update over public channels and constructs a session key establishment mechanism that integrates long-term and ephemeral secrets, thereby enhancing resistance against key leakage, including perfect forward secrecy and KCI attacks. In addition, a dynamic pseudonym mechanism with real identity traceability is designed to achieve conditional privacy preservation, ensuring anonymity and unlinkability while enabling traceability when necessary. As a result, the proposed scheme simultaneously satisfies key security requirements, including public-channel registration, resistance to key-compromise attacks, and conditional privacy preservation, within a unified framework.The security of the proposed protocol is rigorously proven under the Real-or-Random (ROR) model and formally verified using the ProVerif tool. Comparative results reveal that our protocol achieves a 27.74% reduction in computational complexity and a 18.97% decrease in communication overhead, outperforming comparable protocols.