Protecting Modbus/TCP-Based Industrial Automation and Control Systems Using Message Authentication Codes

Critical infrastructure (CI), such as energy and water distribution systems, is essential for the stability and well-being of the modern society. Industrial automation and control systems (IACSs) form the backbone of CIs and enable the operation of such systems in a safe and reliable manner. However, with the increasing use of industrial Ethernet communication protocols, such as Modbus-over-TCP (Modbus/TCP), once air-gapped IACSs are becoming vulnerable to potential cybersecurity threats. This paper presents a novel method for enhancing the cybersecurity of Modbus/TCP-based IACSs by implementing an authentication method based on message authentication codes (MACs). To provide partial protection of communication even when communicating with legacy Modbus/TCP peers, we propose a novel supervising device that analyzes exchanged messages and verifies the authenticity of the protected messages. To experimentally verify the protection method, a water-treatment cyber-physical system (CPS) was implemented as a digital twin in a programmable logic controller (PLC). The underlying MAC is the Chaskey-12, lightweight MAC defined in IEC 29192-6. It was implemented in the PLC program using the programming languages defined in IEC 61131-3. As an additional contribution, the presented implementation allows protection of communication between PLCs and other Modbus/TCP peers installed in existing IACSs without hardware or firmware modifications. The results show that the method provides protection against network attacks without significantly affecting performance, also demonstrating the feasibility of such protection in IACSs.