In the near future, most new vehicles will be equipped with short-range radios capable of communicating with other vehicles or with highway infrastructure at distances of at least one kilometer. The radios will allow new applications that will revolutionize the driving experience, providing everything from instant, localized traffic updates to warning signals when the car ahead abruptly brakes. While resembling traditional sensor and ad hoc networks in some respects, vehicular networks pose a number of unique challenges. For example, the information conveyed over a vehicular network may affect life-or-death decisions, making fail-safe security a necessity. However, providing strong security in vehicular networks raises important privacy concerns that must also be considered. To address these challenges, we propose a set of security primitives that can be used as the building blocks of secure applications. The deployment of vehicular networks is rapidly approaching, and their success and safety will depend on viable security solutions acceptable to consumers, manufacturers and governments.