Research On Outsourcing Selective Image Encryption Based On Steganography

With the popularization of personal mobile devices, multimedia greatly enrich the method people obtain information. Multimedia are transmitted not only through the personal computers(PCs), but also in smartphones and Pads. Nowadays Digital images play a fairly important role, and they are widely spread in the cellular networks and the Internet, at the same time they bring security problems and unprecedented challenges. Smartphones have limited hardware capability and energy supply, how to effectively ensure the security of the sensitive data of image on a mobile device become an urgent problem. Encryption is acknowledged to be the basic primitive to protect image security and privacy. Image data are usually massive, multidimensional, and high-redundancy; therefore traditional encryption paradigm that treats plaintext as binary stream and encrypts on the entire bit stream is not suitable for image encryption, especially in real-time communication or resource-limited environment. Fortunately, the emergence of cloud computing provides us an effective way out to solve this problem. As the cloud has much more powerful resources, resource-limited devices can outsource selective encryption to the cloud. However, outsourcing in cloud computing results in serious problems regarding security and privacy, since the data should be transmitted to the cloud and will be handled by the cloud.In this paper, we propose a scheme about outsourcing selective image encryption based on steganography. In our scheme, resource-limited client such as a smartphone outsources chaotic selective image encryption to the cloud; the scheme ensures that the cloud is not aware of the existence of plain image during the encryption. The basic idea of our scheme is as follows: First we extract the important information of plain image that is selected for selective encryption, and hide it in a cover image by steganography; the stego image is then sent to the cloud for outsourced encryption; up on receiving the encrypted stego image from the cloud, the client can extract the encrypted important information and get the result of selective encryption by packing it with the rest part of plain image. We have made several contributions, which are listed as follows:① We focus on design rational steganography, in which way the important data of plain image cannot be monitored by the cloud but can be extracted by user after encryption. In this paper, we embed 2bit information into 2 LSBs of the cover image, and use the third LSB of cover image as a flag to indicate the mismatch position. Extensive experiments are conducted to validate the security.② We focus on design effective outsourcing encryption. Outsourcing security image encryption is conducted on stego image, we must ensure that the design of the encryption algorithm is still valid. That is to say, the encryption operation of stego image is equivalent to the original image, and the user can directly use the decryption key for decryption, not relying on the carrier image. In this paper, selective encryption is proposed to only selectively encrypt a portion of important data, and the cloud uses chaotic encryption algorithm as outsourcing encryption. Safety analysis proves that this encryption algorithm can resist the common attack and meet the requirements of outsourcing.③ We make an induction and reorganization of the basic theory and some relevant research achievements of outsourcing selective image encryption based on steganography. In addition, four evaluation metrics, PSNR, Chi-square, difference image histogram(DIH) and the steganalysis method to detect 2LSB embedding are introduced for steganalysis, and PSNR, SSIM, histogram and the correlation between adjacent pixels are introduced for evaluating the encryption effect jointly. Extensive experiments demonstrate the correctness, security, and performance of our scheme.In the end of this dissertation, conclusions, as well as the discussion of the future work in relevant domain in this paper, are given, and the main research content is the security of image processing in cloud computing.