Dynamics of Reputation

Reputation, trust, Dempster-Shafer theory, combining evidence

To enforce security without user enrollment, trust (or reputation) systems were proposed to use experience as crucial information to support cooperation as well as for security enforcement mechanisms. However, use of trust introduces very difficult problems that still discourage from exploitation of trust for security mechanisms. The ability to change trust quickly and react effectively to changes in environment and user behaviour is profound for usability of mechanisms built on top of trust. Dempster-Shafer theory was proposed as a suitable theoretical model for trust computation. Here, we define general requirements for reputation dynamics and demonstrate that Dempster-Shafer theory properties are not as good as is widely thought. On the contrary, simple formulae work.