Design of hierarchical keys for a multi-user-based watermarking system

For a multi-user-based watermarking system, a new scheme for providing the function of secret sharing is proposed. A user-key generating procedure is introduced to generate one master key and several normal keys. By using either of these normal keys, a secret watermark is obtained from the cover image. By referring to the original watermark and all the generated secret watermarks, a public watermark is created and embedded into the cover image. The proposed scheme does not require the original image to be presented during extracting. To reveal the genuine watermark from the watermarked image, except for the super-user who can extract it directly by using the master key, the normal users who share the secret can only achieve it by presenting the shadow watermarks extracted by using their own keys