Using Ontologies to Detect Anomalies in the Sk

This Master's thesis introduces an anomaly detection solution to increase the security of Air Traffic Control Systems against malicious data manipulation threats. At the same time, this detection system can detect emergencies and air traffic rules violations. Air Traffic Control Systems are made of multiple sensors sending data to air traffic controller workstations over an IP network using a publish-subscribe protocol, Data Distribution Service. Malicious data can be inserted into this network by either compromising a machine on the network, or by tricking the sensors into emitting falsified data. Once into the network, the system currently cannot distinguish malicious data from real one and will treat it as such, potentially causing dangerous situations and general confusion that could lead to air traffic safety being compromised.;We quantify the impact different attacks have on the system by building a threat model while considering existing safety procedures already in place in the aviation world. We found that there are multiple ways an attacker can inject malicious data into the system either directly by injecting false data into the network or indirectly by sending spoofed broadcasts that will be picked up by the ground equipment and in turn injected into the network. These data manipulations can induce an air traffic controller into making a wrong decision. This threat model also gives us direction on how to detect potential threats.;To counter these threats, we design a detection solution using ontologies to store data and a query engine to interact with it. By using ontologies, we can add semantics to the data and facilitate the creation of detection queries in the SPARQL query language. It uses a translation table to convert Data Distribution Service data structures into ontological concepts. The detection engine runs on dedicated machines and sends alerts to the concerned computers if a query detects an anomaly. The ontological model was built using the assumptions we made about the data pieces circulating on the Air Traffic Control System's network. Designing an ontology that is specific enough to be useful for detection, but also generic enough to easily add new detection capabilities proved to be a challenge. We found that we often needed to add new concepts to the ontology when we designed new queries.