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 message integrity. 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 privacy thresholds. Copyright © 2008 John Wiley & Sons, Ltd.