Protocols are typically specified in an operational manner by specifying the communication patterns among the different involved principals. However, many properties are of epistemic nature, e.g., what each principal believes after having seen a run of the protocol. We elaborate on a unified algebraic framework suitable for epistemic reasoning about operational protocols. This reasoning framework is based on a logic of beliefs and allows for the operational specification of untruthful communications. The information recorded in the semantic models to support reasoning about the interaction between the operational and epistemic aspects intensifies the state-space explosion. We propose an efficient on-the-fly reduction for such a unifying framework by providing a set of operational rules. These operational rules automatically generate efficient reduced semantics for a class of epistemic properties, specified in a rich extension of modal μ -calculus with past and belief modality, and can potentially reduce an infinite state space into a finite one. We reformulate and prove criteria that guarantee belief consistency for credulous agents, i.e., agents that are ready to believe what is told unless it is logically inconsistent. We adjust our reduction so that the belief consistency of an original model is preserved. We prove the soundness and completeness result for the specified class of properties.

We propose CRYSTAL framework for automated cybersecurity assurance of cyber-physical systems (CPS) at design-time and runtime. We build attack models and apply formal verification to recognize potential attacks that may lead to security violations. We focus on both communication and computation in designing the attack models. We build a monitor to check and manage security at runtime and use a reference model, called Tiny Digital Twin, in detecting attacks. The Tiny Digital Twin is an abstract behavioral model that is automatically derived from the state space generated by model checking during design-time. Using CRYSTAL, we are able to systematically model and check complex coordinated attacks. In this paper we discuss the applicability of CRYSTAL in security analysis and attack detection for different case studies, Temperature Control System (TCS), Pneumatic Control System (PCS), and Secure Water Treatment System (SWaT). We provide a detailed description of the framework and explain how it works in different cases.

Abstract We provide a semantic framework to specify information propagation in social networks; our semantic framework features both the operational description of information propagation and the epistemic aspects in social networks. In our framework, based on annotated labelled transition systems, actions are decorated with function views to specify different types of announcements. Our function views enforce various common types of local privacy policies, i.e. those policies concerning a single action. Furthermore, we specify global privacy policies, those concerning multiple actions, using a combination of modal $\mu $-calculus and epistemic logic. To illustrate the applicability of our framework, we apply it to the specification of a real-world case study. As a fundamental property for the epistemic aspect of our semantic model, we prove that its indistinguishability relations are equivalence relations, namely they are reflexive, symmetric and transitive. We also study the complexity bounds for the model-checking problem concerning a subset of our logic and show that model checking is PSPACE-complete for the studied subset.