A Cryptographic Key Assignment Scheme with Adaptable Time- token Constraint in a Hierarchy

A scheme, which uses flexible cryptographic key management upon adaptable 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. in (18). This cryptographic key assignment scheme based on the difficulty in solving a discrete logarithm, with adaptable time-token constraint, can achieve better security and more efficient management, than the conventional UHAC scheme. Besides, our scheme provides a flexible manner and dynamic key management to increase the availability of user access in UHAC structure.