A rigorous tool-supported methodology for assuring the security and safety of cyber-physical systems

The increased usage of cyber-physical systems in a number of domains poses a unique challenge: how can one be assured of both the security and safety of these systems? While there are a large number of methodologies in the literature for performing security analysis or safety analysis, many of these are not specific to cyber-physical systems and the challenges these pose. Attempts at producing methodologies for security & safety co-analysis have equally met difficulties in terms of reconciling the different approaches and terminology often used by the separate domains. One solution involves the development of a systems theory-based model for understanding how safety, security & other emergent behaviours of systems can be framed and understood. Such an understanding can then be used in a systematic methodology for performing co-analysis in a structured and robust way. This thesis presents a methodology called Security-Enhanced Systems-Theoretic Process Analysis (SE-STPA), based on an underlying model known as Systems-Theoretic Accident & Attack Model and Processes (STAAMP), which combines safety and security analysis into one unified co-analysis method. It represents an evolution on existing work in safety by Leveson [90] and attempts to address several shortfalls of the existing approach in regards to security. SE-STPA is presented with two case studies that were utilised to evolve the methodology into a mature state. Finally, this thesis presents a discussion on future improvements that could be undertaken to develop the methodology further