密文域高嵌入率图像全位面可逆数据隐藏

Objective: In recent years, reversible data hiding (RDH) of encrypted images has attracted considerable attention. The data hider embeds hidden information into a digital image for covert transmission. However, data embedding often causes damage to the original image, which might not be fully recovered after covert transmission. Thus, effectively combining encryption technology and RDH technology for covert transmission of data is necessary. This combinatorial method ensures that images are encrypted and recoverable. Therefore, RDH technology in the ciphertext domain has become a research focus. The algorithms can be roughly divided into two categories: vacating room after encryption(VRAE) and reserving room before encryption(RRBE). The general method of RDH is typically to encrypt a cover image first, then embed hidden information into the encrypted image, and send it to the receiver. The receiver extracts the secret information and decrypts the encrypted image by using the data hiding key and encryption key, respectively. In previous RDH methods, encrypted images have little redundant space, the bit plane utilization of images is low, the embedding capacity is small, and some flipped pixels may lead to image distortion. Method: In this work, the proposed scheme is mainly divided into the following steps: image preprocessing, block tag embedding, image rearrangement, image encryption, data embedding, data extraction, and image decryption. The content owner divides a grayscale image into eight bit planes, each of which is used for data embedding. The pixel value on each bit plane can be viewed as a binary number, and each bit plane is divided into non-overlapping blocks (such as 4 × 4), which are divided into discontinuous blocks (with pixel values of 0 and 1) and continuous blocks (with pixel values of 0 or 1). An image is rearranged by blocks, and the original order of block labels is embedded in the rearranged image. At the same time, the content owner makes pixel prediction on all discontinuous blocks of all bit planes and obtains the prediction map. Images after arrangement are encrypted with a stream cipher. The content owner sends the encrypted image along with the prediction map to the data hider. In the data embedding phase, the data hider embeds the data according to a pixel prediction method. For a continuous block, the bottom right pixel is kept unchanged for the recovery of the block, and data are embedded in other positions. As a result, the embedding space of each continuous block is very large. For a discontinuous block, a prediction map is generated, and then a pixel prediction model is used. When the prediction is correct, the corresponding value of the prediction map is 1; otherwise, it is 0. In the discontinuous block, only when the prediction map value is 1, data is embedded at the predicted pixel; otherwise, the predicted pixel remains unchanged without embedding data. Of note, all secret data should be encrypted before embedding. Due to the above data embedding phase, cover images can be restored completely later. The embedding capacity of the discontinuous block is less than that of the continuous block. However, due to the large number of discontinuous blocks in the low bit planes, the embedding capacity of discontinuous blocks is considerable in the whole image. However, in some state-of-the-art schemes, the utilization of low bit planes is not sufficient. The proposed scheme solves the problem by using the pixel prediction model with correction information. The data hider sends marked and encrypted images to the receiver. In the image decryption and data extraction stage, the receiver performs image decryption and data extraction according to different keys. Result: In the experimental process, various RDH algorithms in the ciphertext domain were used, and a large number of comparison experiments were conducted on the eight grayscale test images to comprehensively compare the two aspects of complete reversibility and embedding efficiency. At the same time, a verification experiment was conducted on the BOSSbase and BOWS-2 dataset. Compared with some state-of-the-art schemes, the embedding rate of the scheme in this study was improved by 42.1% on the BOSSbase dataset and 43.3% on the BOWS-2 dataset. The embedding rate of the proposed scheme reached 3.089 5 and 2.932 0 bit per pixel on the BOSSbase and BOWS-2 dataset, respectively. Compared with other schemes, the proposed scheme embeds data on all bit planes. Unlike other state-of-the-art schemes, the proposed scheme can embed data in the low bit planes because of the pixel prediction method with correction information. Other schemes ignore the contribution of low bit planes to data embedding. Conclusion: The proposed scheme provides a large space for embedding additional information and ensures its security. Moreover, it can achieve higher embedding rate, and the image recovery is quite correct by embedding data in different blocks with different ways and using all bit planes of images, which shows the effectiveness of the proposed scheme. The experimental results show that the embedding performance of the proposed scheme is superior to that of other state-of-the-art schemes for the RDH of encrypted images. In future work, we will focus on improving the embedding efficiency of discontinuous blocks and improving the algorithm so as to increase the embedding capacity of low bit planes.