ABSTRACT
VANETs are being advocated as a means to increase road safety and driving comfort, as well as to facilitate tra«c control [5,7]. For example, cars can collectively sense information about tra«c congestion and relay them to other cars, toll stations, or the DMV to facilitate tra«c rerouting. Several other applications can become feasible if vehicles cooperate among themselves to achieve a common goal. When designing a cooperation-based system, it is important to address security and privacy concerns. Ÿe system needs to be robust to noncooperating entities and should ideally be able to detect/punish them quickly. To ensure the authenticity of messages propagated in VANET, a straight-forward method is to use public keys certi¢ed by a certi¢cation authority (CA) to sign the messages. Ÿe certi¢ed public keys are called “pseudonyms.” On the other hand, in order to prevent vehicles from being tracked by identifying the keys that are used, each vehicle can switch among multiple pseudonyms, which are di«cult to correlate to each other. With this approach, it is di«cult for an attacker to identify vehicles by examining the used keys. Ÿe aforementioned scheme has been proposed by many researchers [1,2,9,11,15] and works e«ciently.
