Model Checking Temporal Logics of Knowledge Via OBDDs1

Abstract

Model checking is a promising approach to automatic verification, which has concentrated on specification expressed in temporal logics. Comparatively little attention has been given to temporal logics of knowledge, although such logics have been proven to be very useful in the specifications of protocols for distributed systems. In this paper, we addressed the model checking problem for a temporal logic of knowledge (Halpern and Vardi's logic of CKL_n). Based on the semantics of interpreted systems with local propositions, we developed an approach to symbolic CKL_n model checking via Ordered Binary decision diagrams and implemented the corresponding symbolic model checker MCTK. In our approach to model checking specifications involving agents' knowledge, the knowledge modalities are eliminated via quantifiers over agents' non-observable variables. We then modelled the Dining Cryptographers protocol and the five-hands protocol for Russian Cards problem in MCTK. Via these two examples, we compare MCTK's empirical performance with two different state-of-the-art epistemic model checkers, MCK and MCMAS.