Abstract. Virtual Organizations enable new forms of collaboration for businesses in a networked society. During their formation business partners are selected on an as-needed basis. We consider the problem of using a reputation system to enhance the member selection in Virtual Organizations. The paper identifies the requirements for and the benefits of using a reputation system for this task. We identify attacks and analyze their impact and threat to using reputation systems. Based on these findings we propose the use of a specific model of reputation different from the prevalent models of reputation. The major contribution of this paper is an algorithm (called PathTrust) in this model that exploits the graph of relationships among the participants. It strongly emphasizes the transitive model of trust in a web of trust. We evaluate its performance, especially under attack, and show that it provides a clear advantage in the design of a Virtual Organization infrastructure.

Nowadays many companies understand the benefit of outsourcing. Yet, in current outsourcing practices, clients usually focus primarily on business objectives and security is negotiated only for communication links. It is however not determined how data must be protected after transmission. Strong protection of a communication link is of little value if data can be easily stolen or corrupted while on a supplier's server. The problem raises a number of related challenges such as: identification of metrics which are more suitable for security-level negotiation, client and contractor perspective and security guarantees in service composition scenarios. These challenges and some others are discussed in depth in the article.

The requirements for dynamic Virtual Organization Management have been derived from an analysis of the stateof-the-art in service-oriented enterprise management systems and its preparedness for handling more complex, long-term business interactions with multilateral agreements. It was found that these forms of business interactions are currently not well supported with respect to dynamic configuration of membership and business interactions based on trust, security and contract parameters. This resulted in an architecture that extends the state-of-the-art enterprise systems architecture, as well as the protocols for managing the state and membership of the dynamic Virtual Organization.

In mediated information systems clients and various autonomous sources are brought together by mediators. The mediation paradigm needs powerful and expressive security mechanisms considering the dynamics and conflicting interests of the mediation participants. Firstly, we discuss the security requirements for mediation with an emphasis on confidentiality and authenticity. We argue for basing the enforcement of these properties on certified personal authorization attributes rather than on identification. Using a public key infrastructure such personal authorization attributes can be bound to asymmetric encryption keys by credentials. Secondly, we propose a general design of secure mediation where credentials are roughly used as follows: clients show their eligibility for receiving requested information by the contained personal authorization attributes, and sources and the mediator guarantee confidentiality by using the contained encryption keys. Thirdly, we refine the general design for a specific approach to mediation, given by our prototype of a Multimedia Mediator, MMM. Among other contributions, we define the authorization model and the specification of query access authorizations within the framework of ODL, as well as the authorization and encryption policies for mediation, and we outline the resulting security architecture of the MMM. We also analyze the achievable security properties including support for anonymity, and we discuss the inevitable tradeoffs between security and mediation functionality.

Abstract:In this paper 1 we discuss the security requirements for mediation, and present our approach towards satisfying them, with an emphasis on confidentiality and authenticity. Furthermore we outline the design of the basic security mechanisms for mediators. Our basic approach suitably combines the concepts of credentials, for authentic authorization with some kind of anonymity, and of asymmetric encryption, for confidentiality, and it can be extended to include additional mechanisms like digital signatures and fingerprints. Additionally it adopts the model of role based security policies because of its application orientation and of its potentials to integrate and unify various policies.