差分编码和块压缩的密文域可逆信息隐藏算法

随着数字信息与云存储技术的发展与成熟，密文域可逆信息隐藏算法正逐渐成为通信传输中数据隐私保护的研究热点。如何根据不同载体图像像素的分布特征，对局部区域内像素进行自适应识别编码，实现对载体更彻底地压缩以提升嵌入容量仍具有较大挑战。本文针对密文域可逆信息隐藏算法因载体图像空间利用率不足而导致嵌入容量较低的问题，提出一种基于差分编码和块压缩的密文域可逆信息隐藏算法。首先根据自然图像局部区域内像素强相关性邻位作差，并基于块内最大差值对差值图像矩阵进行分类和自适应编码，同时设计分块置乱和块内像素扩散加密机制保证图像信息安全。然后根据差值像素块自适应编码结果作用在对应的密文图像块上，压缩冗余空间，最后通过位替换嵌入秘密信息。不同于之前算法，本算法对差分编码后的图像进行比特位重排列，从密文图像像素最低有效位开始，标记差值像素的符号位，其余各位面依次标记最小差值比特位。由于加密操作与自适应编码的可逆性，合法接收者可实现对原始明文图像的无损重构和秘密信息的无误提取。实验结果表明，与现有的几类算法相比，本文提出的算法具有更高的嵌入率和更好的安全性，在BOSSbase和BOWS-2两个数据集上的平均嵌入率达到3.027bpp和2.937bpp，在经典测试图像上，平均嵌入率也均提高0.57bpp以上。

Reversible Data Hiding in Encrypted Images with Difference Encodingand Block Compression

With the development and maturity of digital information and cloud computing technology, reversible data hiding in encrypted images are gradually becoming a research hotspot for data privacy protection in communication transmission. It is still a big challenge to realize more complete compression of carriers to enhance embedding capacity by adaptive recognition coding of pixels in local areas based on the distribution characteristics of pixels in different cover images. To address the problem of low embedding capacity of reversible information hiding in encrypted image due to insufficient utilization of redundant space in carrier images, a cipher-text domain reversible data hiding algorithm based on difference coding and block compression is proposed. Firstly, the difference image matrix is classified and adaptively coded according to the maximum difference value within the block based on the difference of strong correlation neighbors in the local area of the natural image, At the same time, the original image is chunked, disrupting the order between blocks and diffusion of pixels within blocks to ensure the image information security. Then, according to the result of the adaptive coding of the difference pixel blocks, the redundant space is compressed on the corresponding encrypted image blocks, and finally the secret data is embedded by bit replacement. Different from the previous algorithm, this paper rearranges the bits of the differential-encoded image, starting from the last significant bit of the cipher-text image pixel, marking the sign bit of the differential pixel, and marking the least differential bit in each of the remaining planes in turn. Due to the reversibility of the encryption operation and adaptive coding, the legitimate receiver can achieve lossless reconstruction of the original plain-text image and error-free extraction of the secret data. The experimental results show that the proposed algorithm has higher embedding rate and better security compared with several existing algorithms, and the average embedding rate reaches 3.027bpp and 2.937bpp on both BOSSbase and BOWS-2 datasets, and the average embedding rate is also improved by more than 0.57bpp on classical test images.