Hierarchical encryption using short encryption keys for scalable access control of JPEG 2000 coded images

This paper proposes an encryption method that uses short keys to enable hierarchical access controls for JPEG 2000 codestreams. The proposed method provides images of various quality levels that may be different from the quality at encoding, though it uses a single codestream and a single managed key (masterkey). Only one key generated from the masterkey is delivered to a user authorized to access a reserved quality image. This method also stems users´ collusion to access superior-quality images. Some conventional methods of this proposed method serve the above features, but those keys are much longer than the proposed method. The proposed method uses the smaller number of partial keys than the conventional methods.