“…A central problem for privacy-respecting reputation systems is that they must guarantee that users cannot abolish negative reputation. This can either be reached by only allowing positive reputation, as proposed by Voss and Androulaki et al [5,6], by making it difficult for the user to distinguish between positive and negative ratings, as proposed in [7] by Steinbrecher, or by a trusted third party. Thereby, this trusted third party can either be an external reputation provider, as proposed by Pingel et al and Anwar et al [8,9] or a trusted platform module for the user, as proposed in [10,5] by Kinateder et al and Voss. Anonymity of the users involved is not as easy as just using anonymizing services on the network layer.…”