ACCESS CONTROL

Distance-bounding protocols can o er protection against attacks on access control systems that require users to both verify their credentials and prove their location. However, tradeo s among accuracy, cost, and privacy are necessary. M any access control problems implicitly require access-seeking parties to not only verify their credentials but also prove their location. For instance, in an automobile’s electronic lock and ignition system, a driver carries a token that activates the lock and the ignition only if the token’s validity and proximity can be veri ed. Verifying both is necessary; otherwise, the sys-tem becomes vulnerable to man-in-the-middle a acks. Although proximity can be guaranteed through signal fading, it can be easily circumvented through active relays. For example, an adversary could simply use the Internet to relay messages between a token in a user’s house to the vehicle. Many systems are susceptible t