The open and dynamic nature of modern distributed systems and pervasive
environments presents significant challenges to security management. One
solution may be trust management which utilises the notion of trust in order to
specify and interpret security policies and make decisions on security-related actions.
Most trust management systems assume monotonicity where additional information
can only result in the increasing of trust. The monotonic assumption
oversimplifies the real world by not considering negative information, thus it cannot
handle many real world scenarios. In this paper we present Shinren1, a novel
non-monotonic trust management system based on bilattice theory and the anyworld
assumption. Shinren takes into account negative information and supports
reasoning with incomplete information, uncertainty and inconsistency. Information
from multiple sources such as credentials, recommendations, reputation and
local knowledge can be used and combined in order to establish trust. Shinren
also supports prioritisation which is important in decision making and resolving
modality conflicts that are caused by non-monotonicity.