Research On Selective Image Encryption Based On Digital Chaos

In recent years, computer technology and the Internet is developing rapidly and dramatically changing people's life. Multimedia is a newly born technology which is generated accompanied with these two technologies. Therefore, to protect the security of multimedia information has become a growing consideration. It is widely agreed that the cryptography is the important method to resolve it. Because of the large size of multimedia data, it will cost more resources and time if people encrypt the whole bunch of data. Therefore, selective encryption becomes an important tool. Digital image is a kind of multimedia information, and the research results can be extended to other media forms. During the image transmission process, we use two kinds of encryptions: the confidentiality encryption and the degradation encryption for different purposes. In the image degradation encryption, in order to meet the purchasing model of"try before you buy", it allows users to see a part of the image before they decide to buy. If the user is interested in the image, we can provide the decryption keys to him online or offline so he can decrypt the image to get full details. According to the natural characteristics of image information, we found that some of the traditional image encryption algorithms are not suitable in practical applications because there are many flaws and shortcomings. In recent years, many scholars have put forward some new encryption algorithms for image degradation, but these algorithms also have shortcomings and deficiencies. Therefore, in this paper, we present an image degradation encryption algorithm which leverages the advantages of wavelet transform and the characteristics of chaotic map which are used to select the main information of image and overcome the previous deficiencies respectively. Confidentiality encryption is a traditional image encryption mode which preserves the main content of the image against assaulted and the encrypted image information showing a kind of pseudo-random patterns which can prevent unauthorized users to steal or use. In this paper, we combine the advantages of arithmetic coding and the characteristics of bit-plane to select the main information and the advantages of chaotic map. We improve the RAC which had been existed, and propose a novel image selective encryption algorithm. The main research of this paper is selective encryption. Encrypting the unimportant digital image information can get the image degradation effects, and encrypting the main information of the digital image can achieve the confidential encryption results. Some contributions accomplished in this dissertation are as follows:1. We carry an in-depth research and analysis on selective encryption of image degradation and image confidentiality, and expound their principles and characteristics respectively. We also point out their shortcomings in related applications.2. We propose a selective encryption algorithm of image degradation based on the wavelet transform which combined the characteristics of wavelet transform and the advantages of chaotic map. It translates images from the space domain into the frequency domain, and use chaotic maps to the high frequency after wavelet transform in order to achieve the purpose of image degradation. Then it takes the extent of degradation analysis and safety analysis of the experimental results. The results show that this algorithm can effectively resist various filtering attacks and the average attack. It can also get good degradation effect to meet the needs of Internet sales.3. Based on the review of the knowledge of arithmetic coding and arithmetic coding theory, we summarize the arithmetic coding from various aspects which found some advantages by comparing it with some other traditional code methods. We also analyze its advantage for compression.4. We describe the random arithmetic coding (RAC) which is proposed by Grangetto et. al. and find its inadequate. We improve the RAC by combining it with the characteristics of bit-plane and the advantages of chaotic maps. Then we propose a new selective encryption algorithm which based on the arithmetic coding. We also analyze its safety and efficiency. Results show that the algorithm can resist the various existing attacks and other cryptanalysis. It is a safe and effective algorithm.Finally, the thesis is concluded. Some deficiencies as well as further work are also given.