Stochastic Models for Combined Security and Dependability Evaluation

Security is a topic of ever increasing interest. Today it is widely accepted that, due to the unavoidable presence of vulnerabilities, design faults and administrative errors, an ICT system will never be totally secure. Connecting a system to a network will necessarily introduce a risk of inappropriate access resulting in disclosure, corruption and/or loss of information. Therefore, the security of a system should ideally be interpreted in a probabilistic manner. More specifically, there is an urgent need for modelling methods that provide operational measures of the security. Dependability, on the other hand, is the ability of a computer system to deliver service that can justifiably be trusted. In a dependability context one distinguishes between accidental faults, which are modelled as random processes, and intentional faults, i.e., attacks, which in most cases are not considered at all. A major drawback of this approach is that attacks may in many cases be the dominating failure source for today’s networked systems. The classical way of dependability evaluation can therefore be very deceptive: highly dependable systems may in reality fail muc