Comprehensive evaluation of key management hierarchies for outsourced data

Key management is an essential component of a cryptographic access control system with a large number of resources. It manages the secret keys assigned to the system entities in such a way that only authorized users can access a resource. Read access control allows read access of a resource by the authorized users and disallows others. An important objective of a key management is to reduce the secret key storage with each authorized user. To this end, there exist two prominent types of key management hierarchy with single key storage per user used for read access control in data outsourcing scenario: user-based and resource-based. In this work, we analyze the two types of hierarchy with respect to static hierarchy characteristics and dynamic operations such as adding or revoking user authorization. Our analysis shows that the resource-based hierarchies can be a better candidate which is not given equal emphasis in the literature. A new heuristic for minimizing the key management hierarchy is introduced that makes it practical in use even for a large number of users and resources. The performance evaluation of dynamic operations such as adding or revoking a user’s read subscription is shown experimentally to support our analytical results.