Study On Reversible Data Hiding Algorithm In Encrypted Medical Image

“Internet + medical” system is becoming a focus of public attention.Medical image as an important basis for medical diagnosis is transmitted and flowed in the public communication network.However,the public network has a large number of subscribers.Criminals may engage themselves in illegal activities to benefit them by utilizing the concealment and convenience of the network.It makes the medical images,which contain the sensitive information about patients,become the target of attacker,and then be intercepted and tampered.Malicious attacks can interfere with the doctor's diagnosis,cause mental and physical injuries to patients and their family.Therefore,the security protection of medical images is a serious and challenging problem.Image encryption and reversible data hiding technology can protect the security of medical images.Encryption technology can protect the content confidentiality so that plaintext information is not visible.Reversible data hiding is to protect the integrity of the content to determine whether the content is tampered or reliable.In the complex application environment,it is often necessary to combine the encryption technology and reversible data hiding technology to realize the double content protection of the confidentiality and integrity.The main works of this thesis include the following aspects:(1)The related digital image encryption algorithms,reversible data hiding algorithms,and reversible data hiding algorithms for encrypted images are researched and analyzed.(2)The present algorithms have the disadvantages,such as low embedding capacity,region of interest(ROI)partition and the inflexible operation at the receiver.By combining with the characteristics of medical images,a novel separable reversible data hiding method in encrypted medical images is proposed in this thesis.First,the medical image with 256 gray levels is decomposed into eight bit-planes,and the highest four bit-planes are compressed,which leaves some space to fill the peak.Then the image is reconstructed.The head,middle,tail of the reconstruct image are encrypted,respectively.After that,information is embedded in the encrypted image by histogram technique,which chooses position with the data hiding key in the tail.For the receiver,information extraction and image restoration can be separated according to the keys.Experimental results demonstrate that compressed image leaves some space to store information,and avoid the auxiliary information transmission,effectively improve the embedding capacity and reduce the computational complexity.After extracting the private data,the carrier image can be recovered fully.(3)In order to carry out the authentication of the watermarked image,by combining the homomorphic public key encryption technology and the LSB algorithm,the improved separable reversible data hiding algorithm for encrypted medical image is proposed.Compared with the proposed algorithm in(2),this algorithm can extract the secret data from watermarked plain image.This algorithm has extended the application background,and increased the embedding rate and the value of PSNR.After extracting the secret data,the carrier image can also be recovered fully.