Quantitative estimates of critical infrastructures' interdependencies on the communication and information technology infrastructure

Interdependencies of critical infrastructures on communications and information technology infrastructure (CITI) are known collectively as cyber interdependency, which has significant impact on many critical infrastructures. However, till now no formal relationship has been proposed to estimate cyber interdependencies. In this paper, we present a set of empirical functions to represent cyber interdependencies for different critical infrastructures. Our approach is based on identifying important CITI services for each of these infrastructures and systematically ranking them according to their contribution to the infrastructures' output. The description of interdependencies between infrastructure entities in functional form is rooted in system theory and is an essential component of computational modelling and simulation. The work presented in this paper is a pioneering attempt to formalise cyber interdependencies for different critical infrastructures from a system engineering approach.