In Intelligent Transport Systems (ITS), Vehicular Ad-hoc Networks (VANET) play an essential role in improving road safety and traffic efficiency. Nevertheless, due to its special characteristics like high mobility, large size of the network and dynamic topology make routing of data in the vehicular ad hoc network more challenging. The problem in these networks is to determine the routing protocol best suited to this environment, and then secure it to provide optimal and secure routing for the data. Recently, position-based routing protocol has been developed by researchers to be a very interesting routing technique for communication between vehicles. In this paper, we propose an secured and enhanced version of the Greedy Perimeter Stateless Routing (GPSR) protocol. This protocol consists of two modules: (i) To implement an improvement of GPSR routing protocol which minimizes transfer delays and control messages. (ii) To deal with security issues, we have proposed a solution that combines between an improved Diffie-Hellman algorithm for reliable key exchange and the hash function based Message Authentication Code (MAC) for the verification of the authentication and integrity of GPSR packet. The proposed solution was checked by the security protocol verification tool, Automated Validation of Internet Security Protocols and Applications (AVISPA), which indicated that it is a very secure level. Simulation results showed that our proposed compared to the original GPSR offers better performances.