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We first describe a metric for uncertain probabilities called opinion, and subsequently a set of logical operators that can be used for logical reasoning with uncertain propositions. This framework which is called subjective logic uses elements from the Dempster-Shafer belief theory and we show that it is compatible with binary logic and probability calculus.

Reputation systems can be used in online markets and communities in order to stimulate quality and good behaviour as well as to sanction poor quality and bad behaviour. The basic idea is to have a mechanism for rating services on various aspects, and a way of computing reputation scores based on the ratings from many different parties. By making the reputation scores public, such systems can assist parties in deciding whether or not to use a particular service. Reputation systems represent soft security mechanisms for social control. This article presents a type of reputation system based on the Dirichlet probability distribution which is a multinomial Bayesian probability distribution. Dirichlet reputation systems represent a generalisation of the binomial Beta reputation system. The multinomial aspect of Dirichlet reputation systems means that any set of discrete rating levels can be defined. This provides great flexibility and usability, as well as a sound basis for designing reputation systems.

Trust network analysis with subjective logic (TNA-SL)

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Abstract.Research in information security has traditionally focused on where to place or how to propagate trust. In that sense, a cyptographic algorithm or protocol is simply a mechanism to transfer trust from where it exists to where it is needed. This paper puts the focus on trust itself and shows that it is a very complex concept with many interesting and important implications. We do not attempt to define a formal trust model, but rather examine the types of trust and trust relationships which are relevant for information security. It is shown that the existence of trust as a phenomenon depends on the existence of malicious behaviour. This observation leads to the distinction between passionate entities with human-like capabilities, and rational entities which basically are systems. Dust can then be defined as the belief that a rational entity will resist malicious manipulation or that a passionate entity will behave without malicious intent. It is also shown that trust relationships exhibit a great diversity, that they are based on knowledge and that they contain aspects in common with stmtegy games.

Abstract. Trust propagation is the principle by which new trust relationships can be derived from pre-existing trust relationship. Trust transitivity is the most explicit form of trust propagation, meaning for example that if Alice trusts Bob, and Bob trusts Claire, then by transitivity, Alice will also trust Claire. This assumes that Bob recommends Claire to Alice. Trust fusion is also an important element in trust propagation, meaning that Alice can combine Bob's recommendation with her own personal experience in dealing with Claire, or with other recommendations about Claire, in order to derive a more reliable measure of trust in Claire. These simple principles, which are essential for human interaction in business and everyday life, manifests itself in many different forms. This paper investigates possible formal models that can be implemented using belief reasoning based on subjective logic. With good formal models, the principles of trust propagation can be ported to online communities of people, organisations and software agents, with the purpose of enhancing the quality of those communities.