Security Implications of Implementing Multistate Distance-Bounding Protocols
Jingyi Zhang, Anjia Yang, Qiao Hu, Gerhard Petrus Hancke · 2019
A number of distance-bounding protocols have proposed multistate exchanges. In theory this can potentially improve the security of the protocol when using the same number of exchange rounds, i.e. as there are more than two states the probability of an attacker guessing a response correctly is lower. Similarly, for the same security probability, multistate distance-bounding protocols require less rounds. On the other hand, transmission errors during the timed exchange phase of the distance-bounding protocol also impact on the security of the protocol, as the verifier needs to allow a certain acceptance threshold of incorrect responses. This threshold causes False Acceptance and False Rejection in protocols and further influences the security of the protocol. In this paper, we investigate the security implications of multistate channel implementation and symbol energy considering their effect on the acceptance threshold. We show that implementing multistate responses using simple m- ary modulation methods found in contactless devices, does not necessarily provide the expected security improvement when devices have finite transmission energy to spend on challenge-response exchanges.