Analysing Likelihood Using CORAS Diagrams

Assigning likelihoods to the unwanted incidents of CORAS diagrams is a necessary prerequisite for risk estimation. This chapter explains how CORAS diagrams can be used to analyse and reason about likelihoods of threat scenarios and unwanted incidents. The likelihoods can be given in terms of probabilities or frequencies, and as precise values or as intervals. We explain how to calculate the likelihood of a given threat scenario or unwanted incident based on likelihoods assigned to other diagram elements, and we explain how to check the consistency of the likelihoods of a CORAS diagram. The likelihood analysis is supported by explicit rules that are presented in this chapter. The chapter furthermore explains how to restructure diagrams in order to enable and facilitate further reasoning about likelihoods.