  Mobile autonomous systems, robots, and cyber-physical systems rely on
accurate positioning information. To conduct distance-measurement, two devices
exchange signals and, knowing these signals propagate at the speed of light,
the time of arrival is used for distance estimations. Existing
distance-measurement techniques are incapable of protecting against adversarial
distance enlargement---a highly devastating tactic in which the adversary
reissues a delayed version of the signals transmitted between devices, after
distorting the authentic signal to prevent the receiver from identifying it.
The adversary need not break crypto, nor compromise any upper-layer security
protocols for mounting this attack. No known solution currently exists to
protect against distance enlargement. We present \textit{Ultra-Wideband
Enlargement Detection} (UWB-ED), a new modulation technique to detect distance
enlargement attacks, and securely verify distances between two mutually trusted
devices. We analyze UWB-ED under an adversary that injects signals to
block/modify authentic signals. We show how UWB-ED is a good candidate for
802.15.4z Low Rate Pulse and the 5G standard.
