Editorial for the special issue on “fault trees and attack trees: Extensions, solution methods, and applications”

Fault Trees are well-known models for the reliability analysis of systems, used to compute several kinds of qualitative and quantitative measures, such as minimal cut-sets, system failure probability, sensitivity (importance) indices, etc. Fault Trees represent the possible combinations of component failures leading to system failure by means of logic gates (or ports). During the years, Fault Trees have been extended to increase their modeling power and deal with component dependencies, multistate components, repair, etc. The modeling elements introduced to this end, such as new gates, required the definition of new solving procedures, typically based on the Fault Tree conversion into other models, such as Binary Decision Diagrams (BDD), Markov chains, Petri nets, Bayesian networks, etc. Besides their application in reliability analysis, Fault Trees have been exploited to model attack modes and evaluate the security level of systems. In this field, they are called Attack Trees and have been extended to represent both attacks and countermeasures. Software tools and libraries for Fault/Attack Trees have been developed and improved over the years. The goal of this Special Issue is to collect recent developments in Fault/Attack Tree extensions, solution methods, software tools, and applications in reliability/security evaluation.