The impact of key assignment on VANET privacy

There are two underlying principles that guide how a vehicular ad hoc network (VANET) is built: there will be misbehavior and the extent to which vehicles can misbehave should be bounded. Additionally, the main use for VANETs currently is to enable safety applications where vehicles' position, velocity, and acceleration are broadcast to other vehicles in the VANET. Combining these guiding principles with this application results in the privacy of vehicles and users being an important concern for VANET design. Safety application messages are signed using keys and therefore linked to vehicles. In this work, we investigate how to assign keys to vehicles in order to preserve privacy and maintain our guiding VANET design principles. Specifically, we investigate the design space where individual keys may be given to multiple vehicles and vehicles may have multiple keys. Through a simple security analysis, we eliminate the case where all keys are common. Through mathematical and logical analysis, we conclude that keys should not be owned by multiple vehicles, that is, keys should be unique to vehicles and vehicles should be given multiple keys. Specifically, we show that it is impossible to provide good privacy and fast revocation when keys are shared among vehicles.