Physical and MAC Layer Techniques for Secure Positioning in Navigation Satellite Systems

Global navigation satellite systems (GNSSs) have become crucial for many applications, both military and civil. Being a widespread technology, there are several motivations to mount attacks against it. To counter these threats, in this chapter, we present GNSS signal authentication techniques operating at both physical and data layers. After a brief introduction of GNSS based positioning, we introduce the main attacks and threats against such a service. Next, we present possible countermeasures, distinguishing between authentication at the system and receiver side. Next, we discuss the use of cross-checks between authenticated and open GNSS observables: these techniques aim at improving the navigation performance by enlarging the set of signals used to compute the position, velocity, and time (PVT), using as anchors the signals authenticated by services such as chips-message robust authentication (CHIMERA) or commercial authentication service (CAS). Finally, we show how a spoofer can tamper the timing information retrieved from the PVT solution computed by a receiver, in a time-spoofing attack. Lastly, we discuss timing assurance techniques.