Abstract-- Vehicular ad hoc networks (VANETs) represent a promising new communication technology that can facilitate many new forms of automotive applications. Many of the applications that will run on these networks will require a high degree of security and privacy. In this paper, we present a robust and efficient security framework for vehicular networks suited for both inter-vehicular and vehicle-to-infrastructure communication. Our system uses identity-based cryptography (IBC) to provide authentication, confidentiality, non-repudiation and messageintegrity. It exploits the implicit authentication provided by IBC to significantly reduce the security/privacy related communication overhead. Additionally it provides scalable, user-customizable security and privacy using short-lived, authenticated and unforgeable, pseudonyms. This feature can be used by VANET applications that require quantifiable trust and privacy to provide differentiated service based on various levels of trust and ...