Markov Model of PLC Availability Considering Cyber-Attacks in Industrial IoT

Abstract

Programmable Logic Controllers (PLCs) are important subsystems in Industrial Internet of Things (IIoT) systems. Recently, sophisticated and targeted cyber-attacks against owners and operators of industrial control systems in IIoT systems have become more frequent. In this work we present a Markov model for assessing the dependability of PLCs in Industrial Internet of Things (IIoT) systems, and its main indicator of availability—the stationary coefficient of availability (AC). We show the AC under the consideration of cyber-attacks, with focus on DoS attacks. The model provides a basis to assess how the dependability of a PLC is affected by cyber-attacks. We describe the states and potential state transitions for the PLC in an IIoT environment with a Markov model. We simulated different use cases based on the model and show with exemplary parameter settings how the probabilities of the states of the PLC’s subsystems can be calculated and how the AC can be derived from the model. Results of the simulation are used to analyze the influence of cyber-attack rates on the PLC availability and it is shown how DoS-attacks impact the PLC’s dependability.