Minimum state awareness for resilient control systems under cyber-attack

State awareness for a control system is the accurate knowledge of the internal states of the system realization. By definition, a cyber-attacker decreases the state awareness by modifying or removing the information available to the operator and control system. By decreasing state awareness, the attacker can directly cause damage to the physical system through the control system, or indirectly by causing the operator to react in a damaging manner to the false information. One of the central problems of resilient control is developing methods to retain the minimal state awareness necessary to continue stable operation during a cyber-attack. The characterization of the necessary minimal state awareness is currently an unanswered question. In this paper, we will define state awareness, discuss the consequences of loss of state awareness, and some potential research directions for maintaining state awareness.