Comparison of two methods to quantify cyber and physical security effectiveness.

With the increasing reliance on cyber technology to operate and control physical security system components, there is a need for methods to assess and model the interactions between the cyber system and the physical security system to understand the effects of cyber technology on overall security system effectiveness. This paper evaluates two methodologies for their applicability to the combined cyber and physical security problem. The comparison metrics include probabilities of detection (P{sub D}), interruption (P{sub I}), and neutralization (P{sub N}), which contribute to calculating the probability of system effectiveness (P{sub E}), the probability that the system can thwart an adversary attack. P{sub E} is well understood in practical applications of physical security but when the cyber security component is added, system behavior becomes more complex and difficult to model. This paper examines two approaches (Bounding Analysis Approach (BAA) and Expected Value Approach (EVA)) to determine their applicability to the combined physical and cyber security issue. These methods were assessed for a variety of security system characteristics to determine whether reasonable security decisions could be made based on their results. The assessments provided insight on an adversary's behavior depending on what part of the physical security system is cyber-controlled. Analysis showed that the BAA is more suited to facility analyses than the EVA because it has the ability to identify and model an adversary's most desirable attack path