# A Methodological Approach to Securing Cyber-Physical Systems for Critical Infrastructures
## 1 Introduction with Grand Challenge
These data play a critical role in facilitating real-time analysis and the identification of potential threats. * **Detect Security Threats:** The OPA utilizes predefined thresholds and advanced machine learning algorithms to identify anomalies and discrepancies between expected and actual system behavior. These detection mechanisms can recognize emerging threats like unauthorized access attempts, data manipulation, and abnormal usage patterns, ensuring the early detection of potential attacks. * **React and Adapt in Real-Time**: The OPA facilitates the automatic reconfiguration of security measures in response to identified threats. This capability enables the system to independently adjust to changing cyber threats by implementing suitable countermeasures, including firewalls, encryption, and user access limitations. Additionally, it includes self-healing functionality, which allows the system to recuperate from security breaches without requiring human intervention. * **Provide Human Oversight**: While automation is crucial for promptly addressing cyber threats, the OPA also incorporates measures for human oversight. Critical decisions, such as significant system reconfigurations or the implementation of specific countermeasures, as well as decisions on security investments based on the allocated budget, can be reviewed and approved by humans, thus maintaining a balance between automation and control. In Figure 1, the proposed OPA enhances the target system (TS) with the mentioned features. It also includes data repositories for storing data and logs for offline analysis, like forensic analysis and formal analysis based on a system model. The OPA components can be integrated into the TS nodes (e.g., monitoring agents within the TS nodes) with support from the TS itself. All capabilities, techniques, mechanisms, and repositories are equipped with well-defined, harmonized, and shared interfaces, rendering the architecture a versatile platform amenable to further extensions. Figure 1 illustrates how the OPA allows the administrator to specify that specific actions, such as selecting between alternative remedies or implementing substantial reconfigurations of the TS, may necessitate human oversight and authorization. Notably, the OPA distinctiveness lies in its adept management of critical, intricate, and dispersed infrastructure, achieved through integrating automated and autonomous detection and response agents with human supervision. The OPA's instrumentation components (monitoring, detection, and reaction) are designed to be protected from cybersecurity threats. They are distributed and potential targets of attacks. OPA components will be designed to operate on the original TS and the combined system, including the OPA components. This will create a self-protecting and self-healing system. This paper presents a multifaceted use case to show that the proposed OPA is feasible and effective. In the following sections, readers will be guided through the process of securing a complex critical infrastructure system, step by step. The use case covers the following key aspects:  
* Identifying security and safety requirements. * Designing and implementing the OPA to meet these requirements. * Validating the system's ability to detect and respond to cyber threats in real time. The use case draws on real-world scenarios involving a Mobile Control Panel (MCP), an IoT framework, and a Robotics Operating System (ROS) testbed, demonstrating how the OPA can be adapted to different types of cyber-physical systems and how it can be considered a foundational guide for cybersecurity professionals, researchers, and system designers tasked with protecting the critical infrastructures that are vital to modern society.