Supervisory Control and Data Acquisition (SCADA) systems have become integrated into many industries that have a need for control and automation. Examples of these industries include energy, water, transportation, and petroleum. A typical SCADA system consists of field equipment for process actuation and control, along with proprietary communication protocols. These protocols are used to communicate between the field equipment and the monitoring equipment located at a central facility. Given that distribution of vital resources is often controlled by this type of system, there is a need to secure the networked compute and control elements from users with malicious intent.
This paper investigates the use of data-driven modeling techniques to identify various types of intrusions tested against a simulated SCADA system. The test bed uses three enterprise servers that were part of a university engineering linux cluster. These were isolated so that job queries on the cluster would not be reflected in the normal behavior of the test bed, and to ensure that intrusion testing would not affect other components of the cluster. One server acts as a Master Terminal Unit (MTU), which simulates control and data acquisition processes. The other two act as Remote Terminal Units (RTUs), these simulate monitoring and telemetry transmission. All servers use Ubuntu 14.04 as the OS. A separate workstation using Kali Linux acts as a Human Machine Interface (HMI), this is used to monitor the simulation and perform intrusion testing. Monitored telemetry included network traffic, hardware and software digitized time series signatures.
The models used in this research include the Auto Associative Kernel Regression (AAKR) and Multivariate State Estimation Technique (AAMSET) [1, 2]. This type of intrusion detection can be classified as a behavior-based technique, wherein data collected when the system exhibits normal behavior is first used to train and optimize the previously mentioned machine learning models. Any future monitored telemetry that deviates from this normal behavior can be treated as anomalous, and may indicate an attack against the system. Models were tested to evaluate the prognostic effectiveness when monitoring clusters of signals from four classes of telemetry: combination of all telemetry signals, memory and CPU usage, disk usage, and TCP/IP statistics.
Anomaly detection is performed by using the Sequential Probability Ratio Test (SPRT), which is a binary sequential statistical test developed by Wald . This test determines whether the monitored observation has mean or variance shifted from defined normal behavior . For the prognostic security experiments reported in this paper, we established rigorous quantitative functional requirements for evaluating the outcome of the intrusion-signature fault injection experiments. These were a high accuracy for model predictions of dynamic telemetry metrics, and ultralow False Alarm and Missed Alarm Probabilities (FAPs and MAPS)...