Transformed-key asymmetric watermarking system

This letter proposes a new asymmetric watermarking system. In the proposed system, a linear transformation A is applied to the primitive key u to form the private encoding key Au and the public decoding key A^-tu, where -t denotes inverse transpose. The transformation mostly cancels out when the decoding key is correlated to watermarked signal containing the encoding key, which is possibly contaminated with noise. Our analysis shows that this simple scheme provides not only reliability in watermark detection but also security from any attempts to identify or erase the "encoding" key. We also address the issue of selecting a good transformation matrix. The proposed system can be made fit for each application by properly designing the transform.