An unsupervised anomaly-based detection approach for integrity attacks on SCADA systems

Supervisory Control and Data Acquisition (SCADA) systems are a core part of industrial systems, such as smart grid power and water distribution systems. In recent years, such systems become highly vulnerable to cyber attacks. The design of efficient and accurate data-driven anomaly detection models become an important topic of interest relating to the development of SCADA-specific Intrusion Detection Systems (IDSs) to counter cyber attacks. This paper proposes two novel techniques: (i) an automatic identification of consistent and inconsistent states of SCADA data for any given system, and (ii) an automatic extraction of proximity detection rules from identified states. During the identification phase, the density factor for the k-nearest neighbours of an observation is adapted to compute its inconsistency score. Then, an optimal inconsistency threshold is calculated to separate inconsistent from consistent observations. During the extraction phase, the well-known fixed-width clustering technique is extended to extract proximity-detection rules, which forms a small and most-representative data set for both inconsistent and consistent behaviours in the training data set. Extensive experiments were carried out both on real as well as simulated data sets, and we show that the proposed techniques provide significant accuracy and efficiency in detecting cyber attacks, compared to three well-known anomaly detection approaches.