1 A Practical Trust Model for Agent-Oriented Electronic Business Applications Sergi Robles 1 , Stefan Poslad 2 , Joan Borrell 1 1 Computer Science Dept., Universitat Autònoma de Barcelona 08193 Bellaterra - Spain 2 Elec. Eng. Dept., Queen Mary University of London E1 4NS London – UK Abstract Agent technology clearly enhances electronic commerce. This somewhat sweeping assertion is easily proved by analyzing new e-commerce agent-based applications: user can trade off-line, use long-term commerce strategies, decide founded on huge quantity of remote information, etc. A problem that arises from using agent technology is security, as it cannot be longer considered from the classical view point. After a closer examination we realize that security is only a bit of a bigger issue: trust. Trust is an extraordinarily complex concept, including lots of hints. Not only technical elements take part in trust, but also social elements. This paper regards to the trust model needed to run secure (trusted) agent-based applications for electronic commerce. One of the more striking aspects of this topic is the taxonomy of trust / distrust. Our model is built on the strength of some structures and a methodology to find trust problems and to design mechanisms to avoid them. The problem we have considered clearly does not admit of an easy solution. Our proposal must be considered as a model of trust for electronic business frameworks. An argument in support of this approach is that it does in fact produce practical results: we show several applications of the model applied on specific scenarios of different projects, focusing on those concerning electronic business. 1 Introduction Agent technology is becoming crucial in electronic business applications. However, there is still a general lack of security in agent-based business. But security is only part of a bigger issue. A dominant element is found when cryptographic protocols are developed to provide security in complex applications. We are referring to protocols used for electronic voting, auctions, business relationships in marketplaces, digital signature of contracts, certificate electronic mail, electronic commerce, and generally, to all those protocols named esoteric cryptographic protocols in [Sch96]. This dominating element is the trust needed among participants in these applications. Trust determines the whole conception of these protocols, especially when multiple participants with opposite interests take part, as is the case in most electronic commerce scenarios. Trust is an extraordinarily complex concept, including lots of hints. Not only technical elements take part in trust but also social elements. Several papers consider trust in