Research On High-fidelity Reversible Data Hiding Of Encrypted Image

With the rapid development of cloud computing in recent years,more and more data are outsourced to cloud storage.However,outsourced storage can easily lead to data privacy leakage.For example,the outsourced data is an image.In order to protect content security,the image always be uploaded to the cloud by an encrypted form.Then the cloud administrator need to embed marked information into the encrypted image for authentication easily.When a user requests to accept image,the cloud administrator can use data extraction keys or image decryption keys according to the user's rights.If the user who only have image decryption keys,he can only obtain decrypted images containing information.If the user who have all keys,he can obtain embedded information and original images.It can implement user's hierarchical authorization.Therefore,reversible data hiding in encrypted image technology has special application scenarios,which attracts many scholars at home and abroad.In this application scenario,users with decryption keys can only obtain decrypted images containing information,in order not to affect the use of these users,the decrypted images must be high fidelity.In order to improve the quality of decrypted image and some stego-images,this dissertation proposes a high fidelity reversible data hiding method in encrypted image.The specific research results are as follows:(1)A reversible data hiding method in encrypted images based on code division multiplexing and difference expansion is proposed.The method use the framework of vacate room after encryption and the property of homomorphic addition.In this method,the secret information can be embedded into the encrypted image in the form of spread spectrum sequence by code division multiplexing technology.Since different spread spectrum sequences can be offset each other,the decrypted image is lossless.In order to further improve the embedding capacity,the information can be embedded according to the reversible data hiding technology based on difference expansion,but it causes partial distortion of the decrypted image.The experimental results show that this method is superior to other recent methods in terms of image quality and embedding capacity.(2)A reversible data hiding method in encrypted images based on image transformation and stitching is proposed.According to the standard deviation of the image block,the secret image blocks and the target image blocks are divided into K categories.Among them,the image blocks of the latter K-T class can obtain a combined image and some auxiliary information through reversible image transformation,and the image blocks of the former T-class can be stitched into the unmatched part of the combined image according to the auxiliary information generated by the transformation of the latter K-T class,so as to hide part of the auxiliary information of the latter K-T class.Note that T is a threshold for balancing the visual quality of transformed images and the amount of auxiliary information.The experimental results show that this method effectively reduces some auxiliary information,and improve the quality of the final stego-image.