Vehicular ad hoc networks VANETs are being increasingly advocated for traffic control, accident avoidance, and management of parking lot and public areas. In particular, communication devices are being installed in more and more cars and roadside infrastructure components. At the same time, they will have direct access to a fixed roadside network infrastructure with information flowing both ways Security and privacy are two major concerns in VANETs. Unfortunately, in VANETs, most Privacy-preserving schemes are vulnerable to Sybil attacks, whereby a malicious user can pretend to be multiple...