Key distribution that has been improved in the system for selective access to information

摘要

A combination of stateless and state-full techniques enable reduced overall key management messages. A set of encryption keys is created based on a stateless subset cover scheme, where each user is associated with a leaf in the subset cover scheme. A state key and a corresponding state representing a subset of users that have the state key and a subset of users that do not have the state key is established, and a subset cover based on information representative of the established state is determined. Finally, a group key management message can be determined at least partly based on the calculated subset cover. The introduced state opens up for efficient subset cover calculation, reducing the size of the key management message.