Study On Chaos-based Digital Image Encryption Technology

With rapid development of multimedia technology and computer network, a huge amount of digital images can be transmitted in Internet. As one of the important means for people to access information, the multimedia security has become a crucial issue that attracted much attention of both the government and the public. However, those images, involving some important information such as national secrets, commercial or individual privacy, can be easily browsed, promulgated or illegally copied if they are not protected. Therefore, the security of image information is becoming the focus of public interest. Meanwhile, image encryption has a wide range of applications in the fields of confidential communications, information hiding and digital watermarking. Studying image encryption is of profound theoretical and practical significance.The contributions of this dissertation can be summarized as follows:Firstly, according to the fact that image encryption in the compression domain based on wavelet transform involves the problem of affecting coding process seriously and reducing the quality of the decryption image by scrambling wavelet coefficients which migrates the position of low-frequency and high-frequency wavelet coefficients resulting in the damage of the tree structure of it, a JPEG2000-based image encryption approach of wavelet coefficients scrambling is proposed in combination with chaotic mapping cryptography, in which the high-frequency subbands are separated into pieces of the same size and scrambled by chaotic mappings in the wavelet domain. Simulation results demonstrate that the proposed approach can decrease the key overhead and compression time overhead, and improve the quality of the decryption image.Secondly, the methods for image encryption using factional Fourier transform are also studied. According to the research of the image encryption using factional Fourier transform with image histogram, this dissertation explores a modified approach to improve the security problem which the method cannot resist the statistical analysis attack by adding some operations to image pixels and reduce the correlation between adjacent pixels of the encrypted image. Experimental results verify the validity of the presented algorithm which can resist the statistical analysis attack.