Dynamics of Reputation

To enforce security without user enrollment, trust (or reputation)systems were proposed to use experience as crucial information tosupport cooperation as well as for security enforcement mechanisms.However, use of trust introduces very difficult problems that stilldiscourage from exploitation of trust for security mechanisms. Theability to change trust quickly and react effectively to changes inenvironment and user behaviour is profound for usability of mechanismsbuilt on top of trust. Dempster-Shafer theory was proposed as asuitable theoretical model for trust computation. Here, we definegeneral requirements for reputation dynamics and demonstrate thatDempster-Shafer theory properties are not as good as is widely thought.On the contrary, simple formulae work.