Biblio

Industrial Control Systems (ICS) are not secure by design–with recent developments requiring them to connect to the Internet, they tend to be highly vulnerable. Additionally, attacks on critical infrastructures such as power grids and nuclear plants can cause significant damage and loss of lives. Since such attacks tend to generate anomalies in the systems, an efficient way of attack detection is to monitor the systems and identify anomalies in real-time. An automated anomaly detection tool is introduced in this paper. Additionally, the functioning of the systems is viewed as Finite State Automata. Specific sensor measurements are used to determine permissible transitions, and statistical measures such as the Interquartile Range are used to determine acceptable boundaries for the remaining sensor measurements provided by the system. Deviations from the boundaries or permissible transitions are considered as anomalies. An additional feature is the provision of a finite state automata diagram that provides the operational constraints of a system, given a set of regulated input. This tool showed a high anomaly detection rate when tested with three types of ICS. The concepts are also benchmarked against a state-of-the-art anomaly detection algorithm called Isolation Forest, and the results are provided.

In this paper, we propose and address the problem of supervisor obfuscation against actuator enablement attack, in a common setting where the actuator attacker can eavesdrop the control commands issued by the supervisor. We propose a method to obfuscate an (insecure) supervisor to make it resilient against actuator enablement attack in such a way that the behavior of the original closed-loop system is preserved. An additional feature of the obfuscated supervisor, if it exists, is that it has exactly the minimum number of states among the set of all the resilient and behavior-preserving supervisors. Our approach involves a simple combination of two basic ideas: 1) a formulation of the problem of computing behavior-preserving supervisors as the problem of computing separating finite state automata under controllability and observability constraints, which can be tackled by using SAT solvers, and 2) the use of a recently proposed technique for the verification of attackability in our setting, with a normality assumption imposed on both the actuator attackers and supervisors.