The advent of intelligent transportation system has a crucial impact on the traffic safety and efficiency. To cope with security issues such as spoofing attack and forgery attack, many authentication schemes for vehicular ad hoc networks (VANETs) have been developed, which are based on the hypothesis that secret keys are kept perfectly secure. However, key exposure is inevitable on account of the openness of VANET environment. To address this problem, key insulation is introduced in our

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... scheme. With a helper device, vehicles could periodically update their own secret keys. In this way, the forward and backward secrecy has been achieved. In addition, the elliptic curve operations have been integrated to improve the performance. The random oracle model is adopted to prove the security of the proposed scheme, and the experiment has been conducted to demonstrate the comparison between our scheme and the existing similar schemes.