# A Methodological Approach to Securing Cyber-Physical Systems for Critical Infrastructures
## 1 Introduction with Grand Challenge  
The emergence of cyber-physical systems has ushered in unprecedented levels of automation and interconnectivity across critical infrastructures. Historically, Operational Technology (OT) systems strongly emphasized operational safety and robustness but often lacked the advanced security protocols in Information Technology (IT) systems. In today's highly interconnected world, critical infrastructures such as power grids, transportation systems, water treatment plants, and healthcare facilities increasingly rely on modern Information and Communication Technology (ICT) infrastructures. These infrastructures, therefore, combine both Information Technology (IT) and Operational Technology (OT), forming complex cyber-physical systems (CPSs). Integrating these systems improves efficiency, automation, and scalability, but also brings about a new set of security and safety challenges. Indeed, critical infrastructures are exposed to new forms of cyberattacks that exploit vulnerabilities in both the physical anddigital domains. For example, incidents like STUXNET [1; 2] highlighted the devastating potential of cyberattacks targeting industrial control systems, resulting in widespread damage to physical systems. Additionally, cyber-physical systems that manage critical infrastructure have become attractive targets for cyberattacks, posing significant national and economic security risks. Their reliance on interconnected systems, data sharing, and instantaneous operational responses makes them susceptible to various threats, including network breaches, malware, distributed denial of service (DDoS) attacks, and complex cyber espionage campaigns. Consequently, as security concerns within these infrastructures become increasingly prominent, integrating IT, OT, and CPS introduces new layers of complexity. For instance, OT, traditionally focused on safety and reliability, must now adopt IT security measures, including data protection, encryption, and threat detection. However, this amalgamation often leads to decreased performance, operational delays, and reduced system efficiency, prompting the following important questions:  
**RQ1:** How can these infrastructures be secured without compromising their performance? **RQ2:** How can systems be developed to identify real-time emerging threats, mitigate their impacts, and recover promptly? These urgent issues present a significant challenge for researchers, engineers, and cybersecurity professionals dedicated to protecting critical infrastructure. To tackle these questions, this paper presents a comprehensive methodological useful approach to design and preliminarily implement an Open Platform Architecture (OPA) to secure critical infrastructure cyber-physical systems. The proposed OPA endeavors to establish a flexible and scalable architecture that integrates existing and newly developed systems seamlessly. It offers advanced security monitoring, threat detection, and automated response mechanisms. The architecture focuses on real-time threat management, enabling autonomous anomaly detection, response, and implementation of self-healing measures to mitigate risks. Emphasizing an open and modular component (hence, the name Open Platform), the proposed architecture allows for the integration of heterogeneous security technologies, ensuring long-term adaptability and resilience against emerging cyberthreats. As shown in Figure 1, the proposed OPA is designed to serve as a foundational blueprint for developing and deploying secure ICT systems in critical infrastructures. It provides a structured approach for integrating advanced security measures, ensuring that system security is treated as a dynamic and evolving feature rather than a static one. The architecture enables critical infrastructures to perform the following:  
* **Monitor and Collect Data:** The OPA system has comprehensive monitoring tools designed to continuously gather data from various system components, including network traffic, user activity, and resource consumption.