A UWB-Based Solution to the Distance Enlargement Fraud Using Hybrid ToF and RSS Measurements

Distance bounding has gained attention in the last decades due to the increasing need for security in applications, such as controlling drones and keyless access control. In such applications, it is important to verify if the two entities participating in a transaction are geographically close to each other. A distance fraud is a known class of attacks in this context, and it has been shown that particular attacks within this class can be successfully applied to any distance estimation approach relying on round-trip time-of-flight (ToF) measurements. In this paper, we show that by combining ToF-based with Received Signal Strength (RSS)-based distance estimations, a system comprising at least two anchors can detect distance reduction and enlargement frauds. The latter so far had no general solution. Providing such a solution constitutes the main contribution of this paper. The proposed solution is based on the fact that the apparent position of the prover is constrained to two different feasibility regions: one for RSS and another for ToF-based measurements. These feasibility regions overlap only at the true position of the prover and get inconsistent with an increasing magnitude of the attack. The proposed hybrid method adds virtually no overhead to a ToF-based system, and not only achieves a tighter bound on distance reduction frauds than the pure ToF method, but (tightly) bounds the distance enlargement fraud, which is currently unbounded when using the pure ToF method. Additionally, it requires only two verifiers, outperforming a well-known solution, which requires at least three verifiers. Simulation results show that when using verifiers separated by just 10 cm, suitable for implementation in a single device, the system is able to detect enlargement frauds as small as 120 cm with a high probability.