An Efficient Time-Bound Access Control Scheme for Dynamic Access Hierarchy

Embedding user subscription time into cryptographic key generation and assignment for hierarchical access control has raised tremendous interest among researchers and practitioners in multicast, broadcast, and secure group communication fields. During the subscription period, a user of a higher class can compute the (time-bound) keys of his/her own class and also derive the keys of all its descendant classes in the access hierarchy. However, after the subscription expires, the user cannot compute/derive the keys. Unfortunately, due to the inclusion of time in the keys, existing schemes either suffer from (colluding) attacks or are only applicable to static access hierarchies. In this paper, we propose a new key generation and assignment scheme for this kind of time-bound hierarchy access control. The new scheme is able not only to prevent colluding attacks but also to support dynamics of access hierarchies in a simple and efficient way.