Abstract—Vehicular ad hoc networks (VANETs), formed bycomputers embedded in vehicles and the traffic infrastructure,are expected to develop in the near future to improve trafficsafety and efficiency. To this end, VANETs should be designed tobe resistant against various abuses and attacks. In this paper, wefirst review the existing proposals to provide security, privacy,and data aggregation in vehicle-to-vehicle communication. Wethen address the fundamental issue of achieving these conflictingproperties in a unified solution, having observed that separateefforts cannot fulfill the VANET design objectives. A set ofnew mechanisms are suggested for efficiently managing identitiesand securely compressing cryptographic witnesses, which areamong the major obstacles to the deployment of strong securitymechanisms in VANETs.