Applications in Vehicular Adhoc NETwork (VANET) require high security for end to end communication especially for sensitive information. It is necessary to restrict the unauthorized users from accessing the VANET services using a trusted infrastructure. In addition, messages exchanged should have minimum authentication delay and communication overhead. In this paper, a novel architecture is proposed for trusted infrastructure using combination of short time certificate and Merkle Signature Scheme. In this architecture, secure VANET communication is achieved using psuedo ID generated by the vehicle and the issue of short certificate by the trusted infrastructure that grants the private public key pairs according to the priority of the messages exchanged. Therefore the message dissemination offers reduced overhead and meets the requirement of VANET communication.