In order to resolve the message safety problem in vehicular ad hoc networks (VANET) and improve traffic efficiency, a privacy-preserving and scalable scheme was proposed for VANET messages authentication, in which identity (ID)-based signcryption was used to help vehicles to secretly receive a secret member key from an RSU, and then the vehicles can anonymously send messages on behalf of the group. The efficiency of the proposal is at least 33% higher better than other existed scheme.