Security Analysis of YKHL Distance Bounding Protocol with Adjustable False Acceptance Rate

A distance bounding protocol enables one entity to determine an upper bound on the physical distance to the other entity as well as to authenticate the other entity. It measures the round-trip time of exchanged messages that normally consist of n rounds of a single-bit challenge and a single-bit response. Let FAR_M and FAR_D be the false acceptance rate against mafia fraud attack and distance fraud attack, respectively. Brands and Chaum designed the first distance bounding protocol that has (FAR_M, FAR_D) = ((½)ⁿ, (½)ⁿ). Recently Yum et al. proposed a flexible distance bounding protocol, in IEEE Communications Letters, asserting that its false acceptance rate (FAR_M, FAR_D) can be chosen from ((½)ⁿ , (½)ⁿ) to ((¼)ⁿ , (³/₄)ⁿ). However, we introduce a new attack that achieves a higher false accep tance rate, where (FAR_M, FAR_D) varies from ((½)ⁿ , (½)ⁿ) to ((½)ⁿ, (½)ⁿ/₂).