A robust watermarking algorithm for encrypted medical images based on DCT encrypted domain

The existing watermarking schemes were designed to embed the watermark information into the original images, which are vulnerable to unauthorized access. In this paper, we have proposed a novel and feasible watermarking algorithm in the encrypted domain. First, we encrypted both original medical image and watermark image by using DCT and Logistic map; Then we embedded watermark into the encrypted medical image. In watermarking embedding and extraction phase, zero-watermarking technique has been utilized to ensure the integrity of medical images. At the end of the paper, we compared the robustness of watermarking algorithm between the unencrypted and encrypted approaches. Results demonstrate that in encrypted domain the proposed algorithm is not only robust against common image process such as Gaussian noise, JPEG compression, median filtering, but can also withstand levels of geometric distortions, which can be utilized in information protection of both original medical images and the watermark images.