Flexible Key Assignment for a Time-Token Constraint in a Hierarchy

A scheme, which uses flexible key management upon time-token constraint for a user hierarchy access control (UHAC) scheme, is proposed in this paper. For adapting the changeability in a UHAC system, we propose a technique of assigning independent time-token which is distributed by a trusted agency server to reply an authorized user for once secure access request. The key feature of the technique is to adapt some secure parameters in distributed time-token for responding to each legal access request. Further, all class keys will be updated proactively by the concept of proactive key management, which makes the advantage that is proven and free from the scenario of the collusive attack example which proposed by Yi et al. (2003).