hoc Networks.

The use of previous direct interactions is probably the best way to calculate a reputation but, unfortunately this information is not always available. This is especially true in large multi-agent systems where interaction is scarce. In this paper we present a reputation system that takes advantage, among other things, of social relations between agents to overcome this problem.

Reputation has been studied in many fields but few formal models have been defined up to now. In this paper we propose a new model for reputation that takes into account the social dimension of agents and a hierarchical ontology structure. This model is a natural extension of other models currently being used in the area of electronic commerce. We show how the model relates to these other systems and provide initial experimental results about the benefits of using a social view on the modeling of reputation.

Abstract. The scientific research in the area of computational mechanisms for trust and reputation in virtual societies is a recent discipline oriented to increase the reliability and performance of electronic communities. Computer science has moved from the paradigm of isolated machines to the paradigm of networks and distributed computing. Likewise, artificial intelligence is quickly moving from the paradigm of isolated and non-situated intelligence to the paradigm of situated, social and collective intelligence. The new paradigm of the so called intelligent or autonomous agents and Multi-Agent Systems (MAS) together with the spectacular emergence of the information society technologies (specially reflected by the popularization of electronic commerce) are responsible for the increasing interest on trust and reputation mechanisms applied to electronic societies. This review wants to offer a panoramic view on current computational trust and reputation models.

this paper we describe how these techniques can be used to improve a reputation system and also how this system can be integrated with a negotiation model to increase the succes of negotiations

A diverse collection of trust-modeling algorithms for multi-agent systems has been developed in recent years, resulting in significant breadth-wise growth without unified direction or benchmarks. Based on enthusiastic response from the agent trust community, the Agent Reputation and Trust (ART) Testbed initiative has been launched, charged with the task of establishing a testbed for agent trust- and reputation-related technologies. This testbed serves in two roles: (1) as a competition forum in which researchers can compare their technologies against objective metrics, and (2) as a suite of tools with flexible parameters, allowing researchers to perform customizable, easily-repeatable experiments. This paper first enumerates trust research objectives to be addressed in the testbed and desirable testbed characteristics, then presents a competition testbed specification that is justified according to these requirements. In the testbed’s artwork appraisal domain, agents, who valuate paintings for clients, may gather opinions from other agents to produce accurate appraisals. The testbed’s implementation architecture is discussed briefly, as well.

this paper we propose two methods to evaluate the effectiveness of the CORE mechanism based on a cooperative game approach and a non-cooperative game approach: the results obtained using the first approach define a lower bound on the number of legitimate nodes in an ad hoc network when the CORE mechanism is adopted while the second approach describe the asymptotical behavior of a selfish node that is controlled by CORE

Countermeasures against node misbehavior and selfishness are mandatory requirements in mobile ad hoc networks. Selfishness that causes lack of node activity cannot be solved by classical security means that aim at verifying the correctness and integrity of an operation. In this paper we outline an original security mechanism (CORE) based on reputation that is used to enforce cooperation among the nodes of a MANET. We then investigate on its robustness using an original approach: we use game theory to model the interactions between the nodes of the ad hoc network and we focus on the strategy that a node can adopt during the network operation. As a first result, we obtained the guidelines that should be adopted when designing a cooperative security mechanism that enforces mobile nodes cooperation. Furthermore, we were able to show that when no countermeasures are taken against misbehaving nodes, network operation can be heavily jeopardized. We then showed that the CORE mechanism is compliant with guidelines provided by the game theoretic model and that, under certain conditions, it assures the cooperation of at least half of the nodes of a MANET. Keywords. Security, Denial of Service Attacks, Simulation, Game Theory. Table of Contents . 1.

The majority of existing trust models is based on three underlying assumptions: (i) proven identity of agents, (ii) repetitive interactions and (iii) similar trusting situations. In our work, we address these assumptions by introduction of simple classification techniques in our mechanism that extends existing trust models, rather than by introduction of a new model. The proposed approach formalizes the situation (context) and/or trusted agent identity in a multi-dimensional Identity-Context space, and attaches the trustworthiness evaluations to individual elements from this metric space, rather than to fixed identity tags (e.g. AIDs, addresses). Trustworthiness of the individual elements of the Identity-Context space can be evaluated using any trust model that supports weighted aggregations and updates, allowing the integration of the mechanism with most existing work. Trust models with the proposed extension are appropriate for deployment in dynamic, ad-hoc and mobile environments, where the agent platform can not guarantee the identity of the agents and where the cryptography-based identity management techniques may be impractical due to the unreliable and costly communication.

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