Hierarchical encryption of multimedia contents for access control

An encryption scheme is proposed that considers hierarchies in media, such as text, images, sound, and so on, in a composite multimedia content to enable versatile access control. In the proposed scheme, a content provider has only one managed key (the master key) for a particular multimedia content, and an user who is permitted to access a reserved content objects in the composite content receives only one key that is subordinately generated from the master key. The key generated from the identical master key is delivered to another user, and this permits the user to access different objects. This scheme introduces a new key concept, namely "unusable key", to keep all objects encrypted in a particular medium and to simultaneously decrypt several objects in other media. The other new key, "numbering key," is also used in this scheme to support simultaneous partial decryption of multiple images that are coded with scalable coding technology. Simulation results show the effectiveness of the proposed scheme.