  In this letter, a resilient path planning scheme is proposed to navigate a
UAV to the planned (nominal) destination with minimum energy-consumption in the
presence of a smart attacker. The UAV is equipped with two sensors, a GPS
sensor, which is vulnerable to the spoofing attacker, and a well-functioning
Ultra-Wideband (UWB) sensor, which is possible to be fooled. We show that a
covert attacker can significantly deviate the UAV's path by simultaneously
corrupting the GPS signals and forging control inputs without being detected by
the UWB sensor. The prerequisite for the attack occurrence is first discussed.
Based on this prerequisite, the optimal attack scheme is proposed, which
maximizes the deviation between the nominal destination and the real one.
Correspondingly, an energy-efficient and resilient navigation scheme based on
Pontryagin's maximum principle \cite{gelfand2000calculus} is formulated, which
depresses the above covert attacker effectively. To sum up, this problem can be
seen as a Stackelberg game \cite{bacsar1998dynamic} between a secure path
planner (defender) and a covert attacker. The effectiveness and practicality of
our theoretical results are illustrated via two series of simulation examples
and a UAV experiment.
