Abstract
Recent security threats against cyber-physical critical power grid infrastructures have further distinguished the differences and complex interdependencies between optimal plant control and infrastructural safety topics. In this paper, we reflect upon few real-world scenarios and threats to understand how those two topics meet. We then propose a practical architectural solutions to address the corresponding concerns. As a first concrete step, we focus on networked industrial control systems in smart grid where several sensing-processing-actuation embedded nodes receive information, make control decisions, and carry out optimal actions. Traditionally, global safety maintenance, e.g., transient stability, is embedded into control and taken into account by the decision making modules. With recent cyber security-induced safety incidents, we believe that the safety-handling modules should also be considered as a part of global trusted computing base (attack surface) for security purposes. Generally, maximizing the system's overall security requires the designers to minimize its trusted computing base. Consequently, we argue that the traditional combined safety-control system architecture is not anymore the optimal design paradigm to follow given existing threats. Instead, we propose PLCLOUD, a new cloud-based safety-preserving architecture that places a minimal trusted safety verifier layer between the physical world and the cyber-based supervisory control and data acquisition (SCADA) infrastructure, specifically programmable logic controllers (PLCs). PLCLOUD's main objective is to take care of infrastructural safety and separate it from optimal plant control that SCADA is responsible for.