Organic Computing (OC) systems differ from classical software systems as the topology and the participating components of the system are not predefined and therefore are subject to unforeseeable change during the systems' runtime. Thus, completely new challenges to the verification and validation of such systems as well as for interactions between system components and, of course, between the system and the user arise. These challenges can be subsumed by the terms trustworthiness or trust.This paper proposes -after exploring the notions and principles of trust in the literature -a definition of trust which encompasses all aspects that define the trustworthiness of an Organic Computing system. It then outlines the different research challenges that have to be tackled in order to provide an understanding of trust in OC-systems and gives perspectives on how this endeavour can be taken on. Current research initiatives in the area of trust in computing systems are reviewed and discussed.

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Reputation is an important aspect of trust. If no direct trust experiences are available, one needs to rely on reputation data from other sources. In this paper we present the Neighbor-Trust metric that exploits these communication capabilities of a network by directly asking all neighbors of a target communication partner for reputation trust data. This results in a reputation path of length one, but also in a vulnerability to attacks by unknown, lying entities that try to promote not trustworthy entities. However, by adding weights for reputation data given by entities and a learning mechanism the Neighbor-Trust metric is able to identify and adapt to lying participants in the network by reducing the weight their reputation data has in future reputation calculations. We present an evaluation for the metric and show how to exclude lying participants from the network.

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