Trust value assignment using model-based testing

Trust is an important aspect of decision making for the distributed computing applications such as electronic commerce and particularly influences the specification of security policy. There is often a level of trust associated with a relationship and there is a problem concerning representation of ignorance (or the unknown) with respect to trust. Josang´s opinion model, based on subjective logic, may be a suitable technique for assigning trust values in the face of uncertainty. However, its major weakness is that it cannot be guaranteed that users will accurately assign values appropriately. In this paper, we attempt to use formal methods in general and testing preorders in particular to model computing systems with regard to trust properties. The principal of trust is represented by the labeled transition systems and the direct trust level can be calculated by the testing preorders. The indirect trust level in the distributed systems is investigated further. Besides, the definition of trust, properties of trust relationships, and types of trust are also discussed.