UWB with Pulse Reordering: Securing Ranging against Relay and Physical-Layer Attacks

Mridula Singh (ETH Zurich, Switzerland), Patrick Leu (ETH Zurich, Switzerland), Srdjan Capkun (ETH Zurich, Switzerland)

Physical-layer attacks allow attackers to manipulate (spoof) ranging and positioning. These attacks had real-world impact and allowed car thefts, executions of unauthorized payments and manipulation of navigation. UWB impulse radio, standardized within 802.15.4a,f, has emerged as a prominent technique for precise ranging that allows high operating distances despite power constraints by transmitting multi-pulse symbols. Security of UWB ranging (in terms of the attacker's ability to manipulate the measured distance) has been discussed in the literature and is, since recently also being addressed as a part of the emerging 802.15.4z standard. However, all research so far, as well as security enhancements proposed within this emerging standard face one main limitation: they achieve security through short symbol lengths and sacrifice performance (i.e., limit the maximum distance of measurement), or use longer symbol lengths, therefore sacrificing security. We present UWB with pulse reordering (UWB-PR), the first modulation scheme that secures distance measurement between two mutually trusted devices against all physical-layer distance shortening attacks without sacrificing performance, therefore simultaneously enabling extended range and security. We analyze the security of UWB-PR under the attacker that fully controls the communication channel and show that UWB-PR resists such strong attackers. We evaluate UWB-PR within a UWB system built on top of the IEEE 802.15.4 device and show that it achieves distances of up to 93m with 10cm precision (LoS). UWB-PR is, therefore, a good candidate for the extended mode of the new 802.15.4z Low Rate Pulse standard. Finally, UWB-PR shows that secure distance measurement can be built on top of modulation schemes with longer symbol lengths - so far, this was considered insecure.