Understanding IEC-60870-5-104 Traffic Patterns in SCADA Networks

The IEC-60870-5-104 (IEC-104) protocol is commonly used in Supervisory Control and Data Acquisition (SCADA) networks to operate critical infrastructures, such as power stations. As the importance of SCADA security is growing, characterization and modeling of SCADA traffic for developing defense mechanisms based on the regularity of the polling mechanism used in SCADA systems has been studied, whereas the characterization of traffic caused by non-polling mechanisms, such as spontaneous events, has not yet been studied. This paper provides a first look at how the traffic flowing between SCADA components changes over time. It proposes a method built upon Probabilistic Suffix Tree (PST) to discover the underlying timing patterns of spontaneous events. In 11 out of 14 tested data sequences, we see evidence of existence of underlying patterns. Next, the prediction capability of the approach, useful for devising anomaly detection mechanisms, was studied. While some data patterns enable an 80% prediction possibility, more work is needed to tune the method for higher accuracy.