Research On Reversible Data Hiding Of Encrypted Images

With the development of computer network technology and multimedia technology, the transmission of digital information becomes very normal. Because digital image has lots of information and high redundancy, it is widely used for transferring information in network. However, digital image suffer from tamper, forgery, illegal duplicate in network, it is an important problem to ensure the secure transmission of digital image.Encryption technology and reversible data hiding technology as two important means to guarantee the transmission of digital image security. Nevertheless, in some special applications need to combine encryption with reversible data hiding techniques. For example:suppose a medical image is stored in a database, and a database administrator can embed notations into an encrypted version of a medical image through a reversible data hiding technique. With notations, the database administrator can manage the image or verify its integrity without the knowledge of the original content, and thus the patient’s privacy is protected. On the other hand, a doctor, having the decryption and extraction keys, can decrypt and restore the image in a reversible manner for the purposed of further diagnosing. Another example, simply for ease of accounting, clients can put some important and privacy information in cloud environment, which may introduce the leakage and abuse of privacy information.This thesis studies reversible data hiding in encrypted images for privacy protection, analyzes the shortcoming of the existing algorithms, two novel schemes for reversible data hiding in encrypted images are proposed. The main works as followed:1) Analyze and conclusion the shortcomings of the existing algorithms.2) Combine the substitution encryption with lossless compression technique, a novel reversible data hiding algorithm in encrypted images is proposed. First, chaotic sequence is used to encrypt the original image by using substitution encryption technique, and then segments the encrypted image into several non-overlapping blocks, collect 3 least significant bits (LSBs) of each encrypted pixel in each block, formulate a sequence, compress each 3 bits into 2 bits by using the Hamming distance between streams, and embed secret bit into the position which obtained by lossless compression. The experimental results show that the proposed algorithm can achieve high embedding rates and steganography quality, the operation in receiving terminal meets the requirement of separation mechanism.3) Combine the sort of smoothness with histogram modification, a novel reversible data hiding algorithm in encrypted image is presented. First, divide the original image into several non-overlapping blocks, sort block in descending of the smoothness of block, and scramble each block in a sequential order, then find three pairs of peak and zero points in histogram of each block and embed secret data by modify the value of peak points. The experimental results demonstrate the proposed algorithm has achieved good image quality, lager the embedding capacity while zero error rate, higher image quality under low embedding capacity.