PATROL-F - a comprehensive reputation - based trust model with fuzzy subsystems

Abstract

One of the most critical issues in distributed systems is security. For an entity to interact with another, it should trust the other entity to ensure the correctness and credibility of its responses. The ideal solution to this concern is to have an environment that is fully trusted by all its entities. However, because such a solution cannot be achieved, research has focused on trust and reputation as means to secure distributed systems. This thesis presents PATROL-F, a comprehensive model for reputation-based trust incorporating fuzzy subsystems to protect interacting hosts in distributed syste ms. In PATROL-F, hosts compute a trust value for other hosts prior to interaction. Hosts whose trust level falls below some threshold, are considered unreliable and are not interacted with; hosts whose trust level is above another threshold are considered reliable and are trusted; and hosts whose trust level falls in between these thresholds are considered in the fuzzy region of trust. PATROL-F accounts for two types of trust: trust in the competence of the host and trust in the reliability of the host to give trusted advice. PATROL-F is a truly unique model incorporating various concepts that are importa nt for the calculation of reputation values and the corresponding decisions of w hether to trust or not. Among the incorporated concepts are direct experiences and reputation values, the credibility of a host to give recommendations, the decay of information with time based on a dynamic decay factor, first impressions, and a hierarchy of host systems. The model also implements the concepts of similarity, popularity, activity, and cooperation among hosts. In addition, PATROL-F includes fuzzy subsystems to account for humanistic and subjective concepts such as the importance of a transaction, the decision in the grey region, and setting the result of interaction. We present simulations of PATROL-F and show its correctness and reliability.