Cryptographic protocols are structured sequences of messages that are used for exchanging information in a hostile environment. Many protocols have epistemic goals: a successful run of the protocol is intended to cause a participant to hold certain beliefs. As such, epistemic logics have been employed for the verification of cryptographic protocols. Although this approach to verification is explicitly concerned with changing beliefs, formal belief change operators have not been incorporated in previous work. In this preliminary paper, we introduce a new approach to protocol verification by combining a monotonic logic with a nonmonotonic belief change operator. In this context, a protocol participant is able to retract beliefs in response to new information and a protocol participant is able to postulate the most plausible event explaining new information. Hence, protocol participants may draw conclusions from received messages in the same manner conclusions are drawn in formalizations of commonsense reasoning. We illustrate that this kind of reasoning is particularly important when protocol participants have incorrect beliefs.
We introduce a new semantics for a logic of explicit and implicit beliefs based on the concept of multi-agent belief base. Differently from existing Kripke-style semantics for epistemic logic in which the notions of possible world and doxastic/epistemic alternative are primitive, in our semantics they are non-primitive but are defined from the concept of belief base. We provide a complete axiomatization and a decidability result for our logic.
order to conveniently represent the properties of belief systems, a logic containing belief modalities is defined; the semantics of this logic are given in terms of the new model. This paper presents an abstract general model for representing the belief systems of resource-bounded reasoning agents. The intuition which underlies this new model is that it is possible The new model is then compared to two other formalisms, to capture the key properties of many different types of belief (the deduction model (Konolige, 1986a) and normal modal system in a structure called a belief extension relation. The logics (Halpern and Moses, 1992)), and is shown to generalise them. Some remarks on implementing the new model are paper shows how such a relation may be derived for any system that satisfies some basic properties. The resulting formalism then presented. The paper begins, in the following section, simple, and yet sufficiently rich that it generalises many other by reviewing previous attempts to formally model belief.