A framework for decentralised trust reasoning.

Recent developments in the pervasiveness and mobility of computer systems in open computer networks have invalidated traditional assumptions about trust in computer communications security. In a fundamentally decentralised and open network such as the Internet, the responsibility for answering the question of whether one can trust another entity on the network now lies with the individual agent, and not a priori a decision to be governed by a central authority. Online agents represent users' digital identities. Thus, we believe that it is reasonable to explore social models of trust for secure agent communication. The thesis of this work is that it is feasible to design and formalise a dynamic model of trust for secure communications based on the properties of social trust. In showing this, we divide this work into two phases. The aim of the first is to understand the properties and dynamics of social trust and its role in computer systems. To this end, a thorough review of trust, and its supporting concept, reputation, in the social sciences was carried out. We followed this by a rigorous analysis of current trust models, comparing their properties with those of social trust. We found that current models were designed in an ad-hoc basis, with regards to trust properties. The aim of the second phase is to build a framework for trust reasoning in distributed systems. Knowledge from the previous phase is used to design and formally specify, in Z, a computational trust model. A simple model for the communication of recommendations, the recommendation protocol, is also outlined to complement the model. Finally an analysis of possible threats to the model is carried out. Elements of this work have been incorporated into Sun's JXTA framework and Ericsson Research's prototype trust model

Trusting an Information Agent

: While the common kinds of uncertainties in databases (e.g., null values, disjunction, corrupt/missing data, domain mismatch, etc.) have been extensively studied, a relatively unexplored form of uncertainty in databases, called inaccurate data, demands due attention. Inaccurate data results when data are contributed by various information agents with some known reliability. Though the data itself is total or complete, the reliability of the data now depends on the agent's reliability. Several issues of this form of data reliability have been reported recently where the reliability of agents were assumed to be known and static. In this paper we address the issue of reliability maintenance of information agents and take the view that the agent reliability is dynamic and is a function of the database knowledge and the agent evidences (facts that are observed to be true or false). We propose a method of quantifying the level of trust (or the agent reliability) that the datab..