Robustness of Trust and Reputation Systems: Does It Matter?

Trust and reputation systems provide a foundation for security, stability, and efficiency in the online environment because of their ability to stimulate quality and to sanction poor quality. Trust and reputation scores are assumed to represent and predict future quality and behaviour and thereby to provide valuable decision support for relying parties. This assumption depends on two factors, primarily that trust and reputation scores faithfully reflect past observed quality, and secondly that future quality will be truly similar to that represented by the scores. Unfortunately, poor robustness of trust and reputation systems often makes it relatively easy to manipulate these factors, so that the fundamental assumption behind trust and reputation systems becomes questionable. On this background we discuss to what degree robustness against strategic manipulation is important for the usefulness of trust and reputation systems in general. This paper is the printed version of the inaugural William Winsborough Commemorative Address at the IFIP Trust Management Conference 2012 in Surat.