Ehicular ad-hoc network (VANET) as the core of Intelligent Transportation System (ITS) enables transfer of data which consists of private information of VANETs users such as exact location among the entities of ITS. Therefore, authentication of users is mandatory to restrict access to this information by any malicious users or attackers. However, the available anonymous authentication schemes in VANET have some drawbacks in security and efficiency. Hence, we propose a new anonymous authentication scheme based on Public Key Infrastructure (PKI). To begin with, our scheme constructs the signature of timestamp using the PKI as authentication proof to improve security. Meanwhile, anonymous authentication is strongly guaranteed in our scheme. Further, we establish secure session keys and provide the method of revealing malicious nodes. Security analysis and performance evaluation indicate that our proposed scheme has superiority in both security and efficiency, and is more suitable for wireless networks.