Image-processing In The Encrypted Domain And Its Applications

With the rapid development of Internet,users are increasingly interested in storing personal data in cloud for conveniently accessing and processing.However,because the Internet events of privacy leak happened frequently in recent years,some people have noticed that they must take some measures to preserve their privacy when they outsourced their data to cloud.In order to protect the data from attackers,a user encrypts it before uploading it to the cloud server.However,traditional data processing methods based on plaintext,in this case,are not suitable for directly processing the data in ciphertext.So,how to process data in the encrypted domain has been becoming a hot research topic,which includes some applications like secure image retrieve,legitimacy check,safety review and so on.Fortunately,based on homomorphic cryptosystems,scholars and researchers have proposed some algorithms for processing signals in the encrypted domain,some of which can be used to design image retrieve schemes and legitimacy check schemes.Due to the signal processing algorithms in the ciphertext domain,the cloud server can process encrypted data without decrypting it.In this paper,we mainly study the methods for processing image data in the encrypted domain.We propose an algorithm for computing image Wavelet invariant moment in the encrypted domain,and based this algorithm we further give a secure image retrieve scheme and a legality review method.Specifically,the main contributions of the paper are as follows:(1)Wavelet invariant moment,a kind of important image features in the image processing field,combines the wavelet transform and geometric moment,and it can well describe images in both global and local scopes.However,it is difficult to compute the Wavelet invariant moment in the encrypted domain,because the computation involves complex numbers and floating numbers which cannot be processed in homomorphic cryptosystem.In this paper,we introduce an algorithm that enables the Paillier cryptosystem to process the complex numbers,and propose a method to compute image Wavelet invariant moment in the encrypted domain.After decryption,Wavelet invariant moment achieved in ciphertext is equivalent to that computed in plaintext,which maintains good image feature description.Further,with the proposed feature computation scheme in the encrypted domain,we design a secure image retrieve scheme,which enables a user to securely search and retrieve images from his/her personal image library on the cloud.The experiment shows that a server cannot get any user's information when completing the protocol and also demonstrates that our scheme has a good performance and robustness.(2)By using the photo-sharing function of cloud,a greate many illegal images are shared and diffused on Internet.Against this problem,we propose a scheme to check the legality of users' images based on the computation method of wavelet invariant moment in the encrypted domain.In this scheme,the user encrypts his image and uploads the encrypted image to the server,and then the server computes the image features as well as the distance between this image and the illegal images in its own database.By the distance,the cloud sever is able to determine whether this image is an illegal one.This scheme can effectively detect illegal images and prevent illegal content from spreading on the Internet.The simulation shows that the proposed scheme has a good recognition rate and can protect the privacy of both the user and the censor,which has a good application prospect.