AbstractAs various applications of vehicular ad hoc networks (VANETs) have been proposed, security has become one of the big research challenges and is receiving increasing attention. In this paper, we propose a secure and an efficient vehicle-to-roadside communication protocol by using the recently developed concepts of a certificate-based cryptosystem. The proposed approach combines the best aspects of identity-based public key cryptography approaches (implicit certification) and traditional public key infrastructure approaches (no key escrow). As compared with the previous works, which were implemented with the traditional public key infrastructure and identity-based public key cryptography, the proposed approach is more secure and efficient.