At any given time, the stability of a community depends on the right balance of trust and distrust. Furthermore, we face information overload, increased uncertainty and risk taking as a prominent feature of modern living. As members of society, we cope with these complexities and uncertainties by relying trust, which is the basis of all social interactions. Although a small number of trust models have been proposed for the virtual medium, we find that they are largely impractical and artificial. In this paper we provide and discuss a trust model that is grounded in real-world social trust characteristics, and based on a reputation mechanism, or word-of-mouth. Our proposed model allows agents to decide which other agents' opinions they trust more and allows agents to progressively tune their understanding of another agent's subjective recommendations.

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Supporting trust in virtual communities

The widespread use of the Internet signals the need for a better understanding of trust as a basis for secure on-line interaction. In the face of increasing uncertainty and risk, users must be allowed to reason flectively about the trustworthiness of on-line entities. In this paper, we outline the shortcomings of current security approaches for managing trust and propose a model for trust, based on distributed recommendations.

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A distributed trust model

Authentication in open networks usually requires participation of trusted entities. Many protocols allow trust to be obtained by recommendation of other entities whose recommendations are known to be reliable. To consider an entity as being trustworthy, especially if there have been several mediators or contradicting recommendations, it is necessary to have a means of estimating its trustworthiness. In this paper we present a method for the valuation of trustworthiness which can be used to accept or reject an entity as being suitable for sensitive tasks. It constitutes an extension of the work of Yahalom, Klein and Beth ([YKB93]).

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Valuation of Trust in Open Networks

We present principles for the design of cryptographic protocols. The principles are neither necessary nor sufficient for correctness. They are however helpful, in that adherence to them would have avoided a considerable number of published errors. Our principles are informal guidelines. They complement formal methods, but do not assume them. In order to demonstrate the actual applicability of these guidelines, we discuss some instructive examples from the literature.

/pdf/prudent-engineering-practice-for-cryptographic-protocols-1giygse2n5.pdf

Prudent engineering practice for cryptographic protocols

A global public-key infrastructure (PKI), components of which are emerging in the near future, is a prerequisite for security in distributed systems and for electronic commerce The purpose of this paper is to propose an approach to modelling and reasoning about a PKI from a user Alice's point of view Her view, from which she draws conclusions about the authenticity of other entities' public keys and possibly about the trustworthiness of other entities, consists of statements about which public keys she believes to be authentic and which entities she believes to be trustworthy, as well as a collection of certificates and recommendations obtained or retrieved from the PKI The model takes into account recommendations for the trustworthiness of entities Furthermore, it includes confidence values for statements and can exploit arbitrary certification structures containing multiple intersecting certification paths to achieve a higher confidence value than for any single certification path Confidence values are measured on a continuous scale between 0 and 1 and, in contrast to previous work in this area, are interpreted as probabilities in a well-defined random experiment

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Modelling a Public-Key Infrastructure

The notion of trust is fundamental in inter-domain authentication protocols. The goal is to develop an effective formalism for explicit expressions of trust relations between entities involved in authentication protocols. Different relevant types of trust are identified and classified. A formalism for expressing trust relations is presented along with an algorithm for deriving trust relations from recommendations. The advantages of the approach are demonstrated by analyzing and comparing the trust relation requirements of a few known authentication protocols. >

R. Yahalom

Papers

Trust relationships in secure systems-a distributed authentication perspective