I. Introduction
Intelligent Transportation Systems (ITS) have been increasing rapidly and Vehicle Ad hoc Networks (VANETs) are considered as a main system for the deployment of ITS-based applications. Furthermore, many services have been developed for vehicular networks, which are sorted in two classes: infotainment and safety services. Most of them rely on various types of data collected and/or disseminated from/to vehicles (ex. Cooperative Awareness Messages - CAM). We can cite as examples the services developed by the CarCoDe project [1]: real-time traffic monitoring and management, local service delivery, and real-time fleet management. Securing these networks is then becoming an important challenge since they are more attractive to attacks due to the relevant information that vehicles can manage. Therefore, our aim is to propose an efficient security mechanism to protect such networks against intruders, taking as a use case the real-time traffic monitoring and management service.