Anomaly Detection and its Adaptation: Studies on Cyber-Physical Systems

Sammanfattning: Cyber-Physical Systems (CPS) are complex systems where physical operations are supported and coordinated by Information and Communication Technology (ICT).From the point of view of security, ICT technology offers new opportunities to increase vigilance and real-time responsiveness to physical security faults. On the other hand, the cyber domain carries all the security vulnerabilities typical to information systems, making security a new big challenge in critical systems. This thesis addresses anomaly detection as security measure in CPS. Anomaly detection consists of modelling the good behaviour of a system using machine learning and data mining algorithms, detecting anomalies when deviations from the normality model occur at runtime. Its main feature is the ability to discover the kinds of attack not seen before, making it suitable as a second line of defence.The first contribution of this thesis addresses the application of anomaly detection as early warning system in water management systems. We describe the evaluation of an anomaly detection software when integrated in a Supervisory Control and Data Acquisition (SCADA) system where water quality sensors provide data for real-time analysis and detection of contaminants. Then, we focus our attention to smart metering infrastructures. We study a smart metering device that uses a trusted platform for storage and communication of electricity metering data, and show that despite the hard core security, there is still room for deployment of a second level of defence as an embedded real-time anomaly detector that can cover both the cyber and physical domains. In both scenarios, we show that anomaly detection algorithms can efficiently discover attacks in the form of contamination events in the first case and cyber attacks for electricity theft in the second. The second contribution focuses on online adaptation of the parameters of anomaly detection applied to a Mobile Ad hoc Network (MANET) for disaster response. Since survivability of the communication to network attacks is as crucial as the lifetime of the network itself, we devised a component that is in charge of adjusting the parameters based on the current energy level, using the trade-off between the node's response to attacks and the energy consumption induced by the intrusion detection system. Adaption increases the network lifetime without significantly deteriorating the detection performance.