Watermarking Algorithm for Encrypted Medical Image Based on DCT-DFRFT

Abstract

Medical image is a special type of information that must be strictly protected. However, when these images are stored and transmitted on the internet, they may be vulnerable to malicious attack with poor security. Therefore, this paper studies the digital watermarking algorithm of encrypted medical image based on DCT-DFRFT (Discrete Cosine transform–Discrete Fractional Fourier transform). First, DCT (Discrete Cosine Transform) and tent map are used to encrypt the original medical image and the watermarking. Then, DCT-DFRFT (Discrete Cosine transform–Discrete Fractional Fourier transform) is applied to extract the feature vectors of the encrypted medical image, and zero-watermarking technology is used to generate the secret key to complete the embedding and extraction. The robustness is verified by calculating the normalized correlation coefficient (NC value) between the embedded and extracted watermarking. The experimental results show that this algorithm is robust to both conventional and geometric attacks.