Distance Bounding with Delayed Responses

Distance-bounding protocols enable the establishment of an upper bound on the distance between two communicating parties in such a way that their degree of proximity can be verified. Most of these protocols rely on multi-rounds of single-bit challenge and response. Therefore, in each round, the probability that an adversary will guess the correct response is 1/2. This letter proposes a new method to increase the number of response states of distance-bounding protocols by injecting intentional delays to each round. Our method can reduce the probability of a correct guess from 1/2 to 1/(2k) for each round, where k is the number of different delays, without significant modifications of underlying protocols. Moreover, it can be applied to passive RFID tags, because it requires no special hardware equipment.