Integrating Six-Step Model with Information Flow Diagrams for Comprehensive Analysis of Cyber-Physical System Safety and Security

An approach for integrating Six-Step Model (SSM) with Information Flow Diagrams (IFDs) is proposed. SSM is a model for Cyber-Physical System (CPS) safety and security analysis, which incorporates six hierarchies of CPS, namely, functions, structure, failures, safety countermeasures, cyber-attacks, and security countermeasures. Relationship matrices are used in SSM to identify inter-relationships between these hierarchies and determine the effect of failures and cyber-attacks on CPSs. Although SSM is a useful tool for CPS safety and security modeling, it lacks guidance for identifying failures and attacks, and selecting adequate set of safety and security countermeasures. To address this issue, an approach for integrating SSM with IFDs is proposed and explained using the water treatment system example.