Persistent Distance Bounding for Mobile Provers

Distance Bounding (DB) protocols help to determine the upper bound of the physical distance between a verifier and a prover, with stated applications in contactless payment systems and access control systems. Myriads of DB protocols have been proposed to aid a verifier in ascertaining whether a prover is located within its expected vicinity, and several attack strategies on proposed DB protocols have been published. So far, DB protocols chiefly focus on instantaneous verification of proximity where, at the conclusion of the protocol, the verifier knows whether the prover is currently within the set bound or not. In this work, we consider a different approach to investigate the feasibility of persistent distance bounding. The core idea is that a persistent distance bounding method would complement existing protocols and give the verifier some indication of whether the prover remains within the determined bound as their communication session continues. This allows the verifier to maintain a session with the prover without continuously running the full distance-bounding protocol. We propose PiBiF (Position-independent Bounding with integrated Flexibility), an algorithm that aids the verifier to establish a stable fingerprint to continually check and monitor the bound between itself and a free-moving prover. This aids DB protocols to be resilient to prover movements while validating the bound. Security considerations and evaluations regarding PiBiF are also presented in this paper.