Limitations on the Usage of Noise Resilient Distance Bounding Protocols Dave Singel´ ee, Bart Preneel COSIC Internal Report Abstract Distance bounding protocols can be employed in mutual entity au- thentication schemes to determine an upper bound on the distance to another entity. As these protocols are conducted over noisy wireless ad- hoc channels, they should be designed to cope well with substantial bit error rates during the rapid single bit exchanges. This paper investigates the robustness to high bit error rates of two important secure noise re- silient distance bounding protocols: the RFID protocol of Hancke and Kuhn (SECURECOMM ’05), and the noise resilient MAD protocol of Singel´ ee and Preneel (ESAS ’07). In order to satisfy the specified design criteria, the bit error rate should not exceed a particular threshold value. The results of our paper help to compare both noise resilient distance bounding protocols in the scenario where they are employed in extremely noisy environments, and assist to choose the appropriate design parame- ters, such as the minimal required number of fast bit exchanges. Keywords: Distance Bounding Protocols, Wireless Sensor Networks, Mutual Entity Authentication. 1 Introduction 1.1 Distance Bounding Protocols Location information can be used to enhance mutual entity authentication pro- tocols in wireless ad-hoc networks. One of the methods to accomplish this, is to employ distance bounding protocols. These protocols have been introduced by Brands and Chaum at Eurocrypt’93 [1] to preclude distance fraud and mafia fraud attacks (also called relay attacks) [4], in which a local impersonator ex- ploits a remote honest user. Distance bounding protocols combine physical and cryptographic properties to determine an upper bound on the distance between verifier and prover. The basic idea is to measure the time of flight during a challenge-response protocol, the main building block of the distance bounding protocol. During n fast bit exchanges, the time between sending a challenge and 1