Stochastic Reachability-Based GPS Spoofing Detection with Chimera Signal Enhancement

Abstract

To provide secure navigation for civilian global positioning system (GPS) users, the Air Force Research Lab (AFRL) has developed the chips-message robust authentication (Chimera) (Anderson et al., 2017) signal enhancement for the GPS L1C signal (GPS Directorate, 2022). Chimera inserts a digital signature within both the navigation message and the pilot channels of L1C to allow civilian users to jointly authenticate both components of the signal (AFRL Space Vehicles Directorate, Advanced GPS Technology, 2019). The AFRL will broadcast and test this signal enhancement on the upcoming Navigation Technology Satellite 3 experimental platform, which will be launched in 2024 (Cozzens, 2021; Divis, 2019, AFRL, 2023). If incorporated within the GPS L1C signal, the Chimera enhancement will be the Abstract To protect civilian global positioning system (GPS) users from spoofing attacks, the U.S. Air Force Research Lab has proposed the chips-message robust authentication (Chimera) enhancement for the L1C signal. In particular, the Chimera fast channel allows users to authenticate the received GPS signal once every 1.5 or 6 s, depending on the out-of-band source utilized for receiving the fast channel marker keys. However, for many moving receiver applications, receivers often use much higher GPS measurement rates, at 5–20 Hz. In this work, we derive a stochastic reachability (SR)-based detector to perform continuous GPS signal verification and state estimation between Chimera authentications. Our SR detector validates the received GPS measurement against any self-contained sensor, such as an inertial measurement unit, in the presence of bounded biases in the sensor error distributions. We demonstrate via Monte Carlo simulations that our detector satisfies a user-defined false alarm requirement during nominal conditions, while successfully detecting a simulated spoofing attack. We further demonstrate that our SR state estimation filter successfully bounds the true state during both authentic and spoofed conditions.