Modeling Resiliency and Its Essential Components for Cyberphysical Systems

This paper presents an initial approach related to modeling resiliency for cyberphysical systems. It discusses the concept and definitions of resiliency and outlines the process of building a model of resiliency. Through analogies with feedback control and fault tolerance, the Design for Resilience is addressed, where the design of the controller component of a cyberphysical system needs to account for potential safety hazards and security threats, with awareness of its internal faults and vulnerabilities. This model is validated against other approaches to modeling resilience described in the literature, followed by a discussion of the resilience metrics. The paper concludes with presenting the strategy of modeling resiliency, based on the assumption that one cannot guarantee absolute protection against attacks, or failures, but can aim at providing successful recovery after disruptions. With safety and security as essential resiliency components, an extended model is proposed involving an attacker, suggesting appropriate performance metric reflecting the distance between the normal state and the degraded state. A model-based environment Möbius, from the University of Illinois, is considered in helping to evaluate resiliency under various operational scenarios.