Abstract: Vehicular ad hoc networks (VANETs) are created for data exchange of intelligent transportation systems (ITS), which have recently attracted great attentions. In an open environment the privacy of the vehicle faces serious threats, so some vehicles do not like to publish their identities. But due to security consideration, a vehicle only wants to exchange information with verifiable partners, which needs identities authentication. There is a contradiction in VANETs. Aiming at this dilemma, an effective solution of the anonymity authentication scheme is proposed in this study. It uses ring signature technology to ensure anonymous authentication and forward security technology to reduce key compromise hazard. Performance evaluation shows this scheme can provide secure information exchange among vehicles and enhance the application of VANETs.