| With the rapid development of cloud computing and the increasing popularitng of mobile smart devices,more and more users choose to upload personal data to cloud servers.In order to protect personal privacy information and data security,users often encrypt the data to be uploaded,then upload the encrypted data to the cloud server,so as to achieve the purpose of protecting data security.Since the increasingly widespread use of image data,therefore more and more encrypted images are emerging from cloud servers,and how to manage and apply encrypted images effectively has become a growing concern in the field of information security.In recent years,researchers have been conducting research data hiding algorithms on encrypted domain-oriented for encrypted image data.Data hiding algorithm for encrypted image mainly realizes the purposes of covert communication,identity authentication and copyright protection by embedding additional data into the encrypted image.Currently,how to improve the embedding performance while ensuring security is an important task in the research of reversible data hiding algorithm for encrypted images.In this thesis,we use pixel prediction,block classification coding and bit-plane compression to study reversible data hiding algorithm for encrypted image,and design three new effective algorithms.They are reversible data hiding via block classification coding and bit plane rearrangement in encrypted images,reversible data hiding in encrypted images via bit-planes block coding compression,and reversible data hiding in encrypted images via arranging blocks of bit-planes,respectively.The main results of this thesis are summarized as follows.(1)A reversible data hiding in encrypted images via block classification coding and bit plane rearrangement is proposed.Because the adjacent pixels of the original image have high correlation,the histogram of pixel prediction error will follow a Gaussian distribution with the approximate center of0.Accordingly,after the prediction error is decomposed into 8 bit-planes,there will be more zero values in the upper bit-planes.Aiming at this characteristic,a reversible data hiding in encrypted images via block classification coding and bit plane rearrangement is designed by using pixel prediction and block classification coding technologies.In the algorithm,first the pixel prediction value is calculated and the prediction error is determined,then the prediction error is decomposed into 8 bit-planes and blocks each bit plane.Then,in order to improve the compression efficiency of the blocks,20 block arrangements are designed to rearrange the blocks.Finally,these blocks are classified according to the number of 0/1 in the block,and the bit-planes are compressed by block classification coding,thus vacating room for embedding secret information.The experimental results show that the algorithm is superior to similar algorithms in embedding performance,and it can restore the original image without loss and has good security.(2)A reversible data hiding algorithm in encrypted images via bit-plane block coding compression is proposed.Traditional reversible image data hiding algorithms mostly divide image blocks into the same block and different blocks according to their contents,in which the same block contains all zeros and all ones.Different from traditional algorithms,this research work will classify blocks from the perspective of space division,and on this basis,a reversible data hiding in encrypted images via bit-plane block coding compression is designed.In the algorithm,first the prediction value of pixels is calculated and their prediction errors are determined,then the error image is decomposed into 8 bit-planes,and each bit-plane is divided into a plurality of non-overlapping blocks.Then,from the perspective of spatial division,each block is divided into two parts: an inner ring and an outer ring,and each block is labeled and classified according to the specific contents of the inner ring and the outer ring.Finally,each block is coded and compressed accordingly to make room for embedding secret information.The experimental results show that the embedding rate of the algorithm on three commonly used data sets is higher than that of four advanced reversible data hiding algorithms in encrypted images.(3)A reversible data hiding in encrypted images via arranging blocks of bit planes is proposed.Considering that there are many zeros in the upper planes of prediction error,a reversible data hiding in encrypted images via arranging blocks of bit planes is designed by classifying and rearranging the blocks in the upper plane.In the algorithm,first the pixel value is predicted and the prediction error is calculated,and then the 8 bit-planes of the prediction error image are divided into non-overlapping blocks,and these blocks are divided into two types,namely uniform blocks and non-uniform blocks.In order to improve the embedding performance,the algorithm not only frees up space from uniform blocks,but also embeds data by using non-uniform blocks.Specifically,according to the specific content of nonuniform blocks,they are further divided into compressible blocks or incompressible blocks,in which compressible blocks can be used to make room for data embedding.Because both uniform blocks and non-uniform blocks are used for data embedding,the embedding performance of the algorithm is improved.The experimental results show that the algorithm has high embedding rate and good performance in visual security. |
