Chuchang Liu

A temporalised belief logic for specifying the dynamics of trust for multi-agent systems

Temporalisation is a methodology for combining logics whereby a given logic system can be enriched with temporal features to create a new logic system. TML (Typed Modal Logic) extends classical first-order logic with typed variables and multiple belief modal operators; it can be applied to the description of, and reasoning about, trust for multi-agent systems. Without the introduction of a temporal dimension, this logic may not be able to express the dynamics of trust. In this paper, adopting the temporalisation method, we combine TML with a temporal logic to obtain a new logic, so that the users can specify the dynamics of trust and model evolving theories of trust for multi-agent systems.

Logical Foundations for Reasoning about Trust in Secure Digital Communication

This paper investigates foundations for the description of, and reasoning about, trust in secure digital communication. We propose a logic, called the Typed Modal Logic (TML), which extends first-order logic with typed variables and modal operators to express agent beliefs. Based on the logic, the theory of trust for a specific security system can be established. Such trust theories provide a foundation for reasoning about trust in digital communication.

Trust in Secure Communication Systems - The Concept, Representations, and Reasoning Techniques

The purpose of communication is the exchange of information among agents. Whether an agent believes a message passed by others to be reliable depends on trust which the agent would put in the system supporting secure communications required. Indeed, every security system depends on trust, in one form or another, among agents of the system. Different forms of trust exist to address different types of problems and mitigate risk in certain conditions. This paper discusses the concept of trust in general, and intends to investigate modelling methodologies for describing and reasoning about trust and agent beliefs.

Verification of reactive systems using temporal logic with clocks

Abstract This paper presents a framework for the specification and verification of timing properties of reactive systems using Temporal Logic with Clocks (TLC). Reactive systems usually contain a number of parallel processes, therefore, it is essential to study and analyse each process based on its own local time. TLC is a temporal logic extended with multiple clocks, and it is in particular suitable for the specification of reactive systems. In our framework, the behavior of a reactive system is described through a formal specification; its timing properties, including safety and liveness properties, are expressed by TLC formulas. We also propose several demonstration techniques, such as an application of local reasoning and deriving fixed-time rules from the proof system of TLC, for proving that a reactive system meets its temporal specification. Under the proposed framework, the timing properties of a reactive system can therefore be directly reasoned about from the formal specification of the system.

Modal tableaux for verifying stream authentication protocols

To develop theories to specify and reason about various aspects of multi-agent systems, many researchers have proposed the use of modal logics such as belief logics, logics of knowledge, and logics of norms. As multi-agent systems operate in dynamic environments, there is also a need to model the evolution of multi-agent systems through time. In order to introduce a temporal dimension to a belief logic, we combine it with a linear-time temporal logic using a powerful technique called fibring for combining logics. We describe a labelled modal tableaux system for the resulting fibred belief logic (FL) which can be used to automatically verify correctness of inter-agent stream authentication protocols. With the resulting fibred belief logic and its associated modal tableaux, one is able to build theories of trust for the description of, and reasoning about, multi-agent systems operating in dynamic environments.

Representation and Integration of Knowledge based on Multiple Granularity of Time using Temporal Logic

Modelling, reasoning about and integrating knowledge based on multiple time granularities in knowledge-based systems is important, especially when talking about events that take place in the real world. Formal approaches based on temporal logics have been successfully applied in many application domains of knowledge-based systems where the notion of dynamic change (that is, evolution of a system through time) is central. This paper presents a methodology based on temporal logic to deal with knowledge based on multiple time granularities in knowledge-based systems. The methodology includes an approach to the representation of timing systems, a method used for representing facts and rules in a knowledge-based system that involve multiple time granularities, and several deductive reasoning techniques

Reasoning about Dynamics of Trust and Agent Beliefs

Many formal frameworks have been proposed for specifying and reasoning about the notion of trust and trust mechanisms in agent-based systems. Typed modal logic (TML) is a logic of beliefs which is suitable for the description of, and reasoning about, trust for multi-agent systems by formalising trust policies of the system and agent meta-beliefs in its security mechanisms. In this paper, by adopting the methodology of Finger and Gabbay for temporalising a logic system, we combine TML with a temporal logic, so that the users can also model evolving theories of trust. In the resulting logic, denoted by TML+, temporal properties of trust and agent beliefs can be expressed in a natural way by combinations of temporal and modal belief operators

A State-Based Model for Certificate Management Systems

A Certificate Management System (CMS) is used to generate, distribute, store and verify certificates. It supports secure electronic communication through its functions. This paper presents a state-based model for certificate management systems. The axiomatization of CMS structures and the security policy followed by CMSs is discussed. The main functions of a CMS, including certificate issuing, certificate revocation and certificate rekeying, are formally described through transitions that change states of the CMS. A major CMS client function, certificate verification, is also formally discussed. With this model, an approach to the formal specification of the structure and behavior of a CMS is provided. The approach is very general, and would be useful in guiding the developer and the evaluator of a CMS with the design, analysis and implementation of the system.

An Axiomatic Basis for Reasoning about Trust in PKIs

Trust is essential to a communication channel. The trust relationships, which play an important role in Public Key Infrastructures (PKIs), need to be formalized for providing a reliable modelling methodology to support secure digital communications. In this paper, we present a typed modal logic used for specifying and reasoning about trust in PKIs. In order to study trust relationships within PKIs, we define TA (a set of trust axioms), TB (a trust base) and TC (a set of trusted certificates). In our method, the trust relation in a given PKI is formalized by trust axioms. Based on trust axioms, an agent can have its own trust base that contains all agents whom the agent trusts, and can derive and extend its trusted certificates set. The trust theory for a given PKI, which consists of our modal logic and a set of trust axioms proposed for the PKI, is the basis of the certificate verification function.

Analysing Stream Authentication Protocols in Autonomous Agent-Based Systems

In stream authentication protocols used for large-scale data dissemination in autonomous systems, authentication is based on the timing of the publication of keys, and depends on trust of the receiver in the sender and belief on whether an intruder can have prior knowledge of a key before it is published by a protocol. Many existing logics and approaches have successfully been applied to specify other types of authentication protocols, but most of them are not appropriate for analysing stream authentication protocols. We therefore consider a fibred modal logic that combines a belief logic with a linear-time temporal logic which can be used to analyse time-varying aspects of certain problems. With this logical system one is able to build theories of trust for analysing stream authentication protocols, which can deal with not only agent beliefs but also the timing properties of an autonomous agent-based system