Abstract

The present thesis proposes resilient methodologies against three different classes of security threats that are involved with Cyber-Physical Systems (CPS). The first problem involves time-delay and Denial of Service (DoS) cyberattacks inflicted on the information telecommunication signals exchanged between subsystems of the CPS. The proposed solution involves a set of equivalent interconnected filters to be located at the input channels of all transceivers at every subsystem in such a way that the output of each filter feeds the input of its neighboring subsystems; hence, cooperative filters. It will be shown that the cooperative filtering scheme is capable of making the CPS resilient to random time-delays that may inflict communication channels, as long as the filters make a connected graph. Theoretical results have been validated through simulation of a controversial CPS application known as the Load Frequency Control (LFC) problem in Smart Grids. The second problem involves Navigation of autonomous vehicles in GNSS denied environments. The thesis proposes a novel cooperative localization filtering scheme in which certain filters are deployed onboard the vehicles to exchange the vehicle's \say{perceived} geographic position obtained from onboard sensors and computational equipment with their neighbor vehicles in a Multi-Agent System (MAS) framework in order to compensate the estimation error associated with individual vehicles, by incorporation of the perceived positioning estimates of other vehicles in the network. Finally, the third and last problem involves authentication of navigation commands (i.e., waypoint and airspeed commands) issued from the Ground Control Stations (GCS) to a vehicle, in which the objective is to authenticate the commands received from a master ground controller at the vehicle and decide whether the commands are legitimate commands (and trustworthy to be obliged by the autopilot to follow) or have to be rejected and replaced by trustworthy alternatives. The vehicles use onboard filters to process waypoint commands to formulate a real-time authentication function in order to build a trustworthy map of the airspace for their future navigation.