Abstract
We propose a formal model for reputation-based trust management. In contrast to credential-based trust management, in our framework an agent's reputation serves as the basis for trust. For example, an access control policy may consider the agent's reputation when deciding whether to offer him a license for accessing a protected resource. The underlying semantic model is an event semantics inspired by the actor model, and assumes that each agent has only partial knowledge of the events that have occurred. Restrictions on agents' behavior are formalized as licenses, with “good” and “bad” behavior interpreted as, respectively, license fulfillment and violation. An agent's reputation comprises four kinds of evidence: completely fulfilled licenses, ongoing licenses without violations or misuses, licenses with violated obligations, and misused licenses. This approach enables precise formal modeling of scenarios involving reputations, such as financial transactions based on credit histories and information sharing between untrusted agents.