Cryptography for a Networked Control System using Asynchronous Event-Triggered Control

Abstract

Networked control systems (NCSs) are control systems in which the control loops are closed through a communication network. These systems usually consist of sensors, actuators, controllers and communication devices. The disruption of these control systems can have a significant impact on public health, safety and lead to large economic losses, e.g. the electric power distribution, natural gas distribution and transportation systems. This indicates the importance of protecting the NCS against a malicious party which is attacking the cyber infrastructure. Hence, the NCS should be able to prevent or survive the attacks attempted by the malicious party. This thesis examines an NCS using a recently presented asynchronous event-triggered implementation. This implementation only uses one bit for each transmission, which largely reduces the total number of transmissions. Implementing an aperiodic controller means that sensor and control communications are limited to instances when the system needs attention. Due to the fact that transmissions only take place when control action is needed, it is imperative that these are not tampered with by a malicious party. Considering the principle of an asynchronous event-triggered based NCS, a security strategy is presented which can deal with eavesdropping, data modification and compromised-key attacks. The strategy consists of three main parts: encryption of the single bit sampling transmissions, key updates to spare the transmitted packages' length and the injection of dummies into the wireless network.