Preventing Cyber-induced Irreversible Physical Damage to Cyber-Physical Systems

Ever since the discovery of the Stuxnet malware, there have been widespread concerns about disasters via cyber-induced physical damage on critical infrastructures. Cyber physical systems (CPS) integrate computation and physical processes; such infrastructure systems are examples of cyber-physical systems, where computation and physical processes are integrated to optimize resource usage and system performance. The inherent security weaknesses of computerized systems and increased connectivity could allow attackers to alter the systems' behavior and cause irreversible physical damage, or even worse cyber-induced disasters. However, existing security measures were mostly developed for cyber-only systems and they cannot be effectively applied to CPS directly. Thus, new approaches to preventing cyber physical system disasters are essential. We recognize very different characteristics of cyber and physical components in CPS, where cyber components are flexible with large attack surfaces while physical components are inflexible and relatively simple with very small attack surfaces. This research focuses on the components where cyber and physical components interact. Securing cyber-physical interfaces will complete a layer-based defense strategy in the "Defense in Depth Framework". In this paper we propose Trusted Security Modules as a systematic solution to provide a guarantee of preventing cyber-induced physical damage even when operating systems and controllers are compromised. TSMs will be placed at the interface between cyber and physical components by adapting the existing integrity enforcing mechanisms such as Trusted Platform Module, Control-Flow Integrity, and Data-Flow Integrity.