Key management for content access control in a hierarchy

The need for content access control in hierarchies (CACH) appears naturally in all contexts where a set of users have different access rights to a set of resources. The hierarchy is defined using the access rights. The different resources are encrypted using different keys. Key management is a critical issue for scalable content access control. In this paper, we study the problem of key management for CACH. We present main existing access control models, and show why these models are not suitable to the CACH applications, and why they are not implemented in the existing key management schemes. Furthermore, we classify these key management schemes into two approaches, and construct an access control model for each approach. The proposed access control models are then used to describe the schemes in a uniform and coherent way. A final contribution of our work consists of a classification of the CACH applications, a comparison of the key management schemes, and a study of the suitability of the existing schemes to the CACH applications with respect to some analytical measurements.