基于DWT密文域图像双水印算法

数字水印是保护数字版权的关键技术,本文首先给出双水印算法形式化的定义,然后基于小波变换(DWT)、SM4分组密码算法和Paillier同态密码,设计了一个密文域双水印算法.在嵌入水印时,将载体图像进行三重DWT变换,将频带集分为加密部分、水平高频LH3水印部分和垂直高频HL3水印部分.利用SM4分组密码和Paillier公钥密码分别对加密部分和水印部分频带系数加密,同时利用Paillier公钥密码体制对数字水印信息进行加密,利用最低有效位(LSB)方法,分别在LH3和HL3的密文域嵌入两个用户水印信息.最后DWT小波逆变换后生成含水印的密文图像.在水印提取时,由于Paillier具有同态特性,实现了在解密后的明文提取水印.实验结果表明,该算法具有加解密速度快,水印的不可见性好等特性.

DWT-Based Double Watermarking in Ciphertext Domain

Digital watermarking is the key technology to protect digital copyright. In this paper, the formal definition of the double watermarking algorithm is given firstly. Then, based on the Discrete Wavelet Transform (DWT), the SM4 block cipher algorithm, and the Paillier homomorphic cipher, a double watermarking algorithm in the ciphertext field is designed. When watermarking is embedded, the carrier image is transformed by triple DWT, and the band set is divided into the encryption part, the horizontal high-frequency LH3 watermarking part, and the vertical high-frequency HL3 watermarking part. The SM4 block cipher and Paillier public-key cipher are used to encrypt the frequency band coefficients of the encryption part and the watermark part, respectively. At the same time, the Paillier public-key cipher scheme is employed to encrypt the digital watermark information, and two user watermarks are embedded in the LH3 and HL3 ciphertext fields with the Least Significant Bit (LSB) method. Finally, a watermark ciphertext image is generated after the inverse wavelet transform of DWT. In the process of watermark extraction, due to the homomorphism of Paillier, the watermark can be extracted from the plaintext after decryption. Experimental results show that the algorithm is capable of fast encryption and decryption and good invisibility of watermarks.