Research On Reversible Data Hiding Algorithm For Encrypted Image

In recent years,computer networks and multimedia technology are developing rapidly.Especially for the rise of cloud technology,more and more digital image resources are storing and procesing in the Cloud Platform.But the images transmission in the network will be in danger of being stolen,tampered and copied.Privacy issues and data security should be paid our attention.On many occasions,in order to protect security of image,the image is first encrypted and then additional data are hidden in the encrypted image,which introduces a new research direction:reversible data hiding in encrypted image.It combines the advantages of encryption technology and reversible information hiding and has great theoretical and practical value.It is a new hot spot in recent years with limited achievements.The main works are as follows.(1)Firstly,this paper introduces the research background and significance of reversible data hiding in encrypted image,describes its research status and presents the related concepts,classic algorithms.(2)Secondly,by analyzing the characteristics and shortcomings of the Zhang's algorithm and other improved algorithms,an improved method is proposed for reversible data hiding in encrypted image when the embedding ratio is considered.A new fluctuation function is presented to evaluate the smoothness of image block.The fluctuation values of blocks are calculated,and then are sorted in ascending order.The blocks that the fluctuation values are smaller are selected to embed data.The number of blocks to be selected depends on the embedding ratio.when the information extraction,the corresponding blocks are selected to extract secret data according to the same rules while using the new fluctuation function.Experimental results show that the new fluctuation function can give a better estimation,meanwhile the proposed method can achieve lower extracted-bit error rate than randomly selecting blocks when the embedding ratio is considered.(3)By using the presented classic algorithms,the images containing much equal pixel have poor quality.Therefore,this paper proposes an improved algorithm for this type of image.Every block in encrypted image is divided into three parts and one part is not flipped.According to the embedded data,one of the other two parts is flipped by using the unbalanced flipping.The 3 LSBs of pixels in one part are flipped and only the first and third bits of other part are flipped.Taking the information embedding rate into account,the error of data extraction is reduced by choosing a smaller block.The experimental results show that the improved algorithm has better performance for the smooth images.