Abstract
Emerging challenges in cyber-physical systems (CPSs) have been encouraging the development of safety and security co-analysis methods. These methods aim at mitigating the new risks associated with the convergence of safety-related systemic flaws and security-related cyber-attacks that have led to major losses in CPSs. Although several studies have reviewed existing safety and security co-analysis methods, only a few empirical studies have attempted to compare their strengths and limitations to guide risk analysis in practice. This paper bridges the gap between two novel safety and security co-analysis methods and their practical implementations. Namely, this paper compares a novel extension of the System-Theoretic Process Analysis (STPA-Extension) and the Uncontrolled Flows of Information and Energy (UFoI-E) method through a common case study. In our case study, the CPS under analysis is a conceptual autonomous ship. We conducted our comparative study as two independent teams to guarantee that the implementation of one method did not influence the other method. Furthermore, we developed a comparative framework that evaluates the relative completeness and the effort required in each analysis. Finally, we propose a tailored combination of these methods, exploiting their unique strengths to achieve more complete and cost-effective risk analysis results.
Highlights
Cyber-physical systems (CPSs) integrate novel infor mation technologies and higher levels of automation into physical world operations
We identify two types of reasons that result in the relative complements in the Venn diagram – i.e. in the results obtained only by one method: 1 Team-specific: reasons associated with the teams using the method 2 Method-specific: generic reasons associated with the safety and security co-analysis methods as such
UCA3 is implicitly covered in UCA2, but we introduce it in Systems-Theoretic Process Analysis (STPA)-Extension to explicitly represent this type of unsafe control actions (UCAs)
Summary
Cyber-physical systems (CPSs) integrate novel infor mation technologies and higher levels of automation into physical world operations. Our compar ative framework accounts for the total working hours used in each method and the level of knowledge of each team as the contributing factors leading to team-specific differences in the analysis results. If both methods were to obtain the same results, the method that facilitates these results in less time would arguably be more costeffective This simplified reasoning assumes the same level of knowledge of the system and comparable expertise as a risk analyst, while it neglects the synergic interactions between the team members. We provide this indicator of working hours alongside the information about the team members, including their knowledge of the system and the tools used for the analysis. By keeping all these factors partially under control and by explicitly illustrating their partial differences, we provide sufficient basis to make the results comparable in a fair context
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