Qualitative Reasoning about Cyber Intrusions

In this paper we discuss work performed in an ambitious DARPA funded cyber security effort. The broad approach taken by the project was for the network to be self-aware and to self-adapt in order to dodge attacks. In critical systems, it is not always the best or practical thing, to shut down the network under attack. The paper describes the qualitative trust modeling and diagnosis system that maintains a model of trust for networked resources using a combination of two basic ideas: Conditional trust (based on conditional preference (CP-Nets) and the principle of maximum entropy (PME)). We describe Monte-Carlo simulations of using adaptive security based on our trust model. The results of the simulations show the trade-off, under ideal conditions, between additional resource provisioning and attack mitigation.