The comprehensive integration of instrumentation, communication, and control into physical systems has led to the study of Cyber-Physical Systems (CPS), a field that has recently garnered increased attention. A key concern that is ubiquitous in CPS is a need to ensure security in the face of cyber attacks. In this paper, we carry out a survey of systems and control methods that have been proposed for the security of CPS. We classify these methods into three categories based on the type of defense proposed against the cyberattacks: prevention, resilience, and detection & isolation. A unified threat assessment metric is proposed in order to evaluate how CPS security is achieved in each of these three cases. Also surveyed are risk assessment tools and the effect of network topology on CPS security. An emphasis has been placed on power and transportation applications in the overall survey. Index Terms-cyber-physical systems, resilient control I. INTRODUCTION Motivated by concerns about sustainability, efficiency, and resiliency, several sectors including energy, transportation, water, and healthcare systems have witnessed significant advances in instrumentation, monitoring, and automation over the past decade. The resulting integration of information, communication, and computation with physically engineered systems demands a detailed investigation into the analysis and synthesis of Cyber-Physical Systems (CPS) so as to realize the desired performance metrics of efficiency, sustainability, and safety. The extensive and intricate presence of cyber components also introduces a vulnerability of unwanted access to these systems. The available communication technologies, referred to as SCADA (Supervisory Control and Data Acquisition), are witnessing significant advances, triggering a shift from protected, closed, and wired networks to open and wireless networks which, as a side effect, are more vulnerable to outside interference.
