基于混沌系统的光学图像加密研究

发布时间：2018-06-23 10:12

本文选题：混沌系统 + 图像加密　；参考：《南京理工大学》2017年硕士论文

【摘要】：信息时代的飞速发展让信息传递更加迅速和便捷,图像信息因其具有形象直观传递信息的特点,无论是在民用领域还是在非民用领域的数据通信中运用的尤为广泛。因此,图像在传递过程中的安全问题也更加值得我们关注。由于图像数据量庞大,冗余性严重,且数据存储结构呈二维空间分布,用传统的加密方式加密效率非常低,需要一种适合图像的新的加密方式来提高加密效率。基于混沌映射与加密系统两者之间的诸多共性,例如:混沌的拓扑传递与混迭特性类似于密码的扩散与混淆特性;混沌对参数的敏感性则对应着密码对密钥的敏感性;混沌映射通过多轮的迭代获得指数分离的轨道,加密系统则通过多轮的置乱与替换将明文打乱。本文的主要工作如下:首先,介绍了密码学和混沌理论的基本概念,为基于混沌理论的图像加密方法研究奠定基础。阐述了光学干涉、菲涅耳衍射、透镜的傅里叶变换的数学模型,为基于混沌理论的虚拟光学加密系统提供了理论基础。其次,提出了一种基于Logistic混沌映射的比特级数字图像加密方法。灰度图像的每个像素值采用八位的二进制数来表示,将二维灰度图转换为一维的0和1的数码串来处理。根据给定的初始值由Logistic映射及生成混沌序列,对混沌序列进行排序,得到位置索引,根据位置索引对原始图像进行比特级的置乱操作,可以达到集像素融合和像素置乱于一体的图像加密结果。然后,进一步提出了一种基于Lorenz混沌系统的比特级彩色数字图像加密算法。针对彩色数字图像的三个分量R、B、G,用Lorenz混沌系统产生的x,y,z三个维度的混沌序列分别进行加密,最后再合而为一。加密时,把每一个十进制的像素值看成是八位二进制数,利用混沌序列的升序排列位置索引进行置乱,达到像素融合的目的,实现图像的加密。最后,将混沌系统和虚拟光学系统统一起来,提出了一种基于混沌的虚拟光学成像加密系统,用混沌序列产生随机相位模板和随机振幅模板,并进行联合调制,相对于传统的随机模板而已,用混沌序列产生随机模板可以减小密钥的体积,提高加密效率。
[Abstract]:With the rapid development of the information age, information transmission is more rapid and convenient. Image information is widely used in both civil and non-civil field data communication because of its characteristics of image and visual information transmission. Therefore, the security of image transmission process is more worthy of our attention. Because of the huge amount of image data, the serious redundancy and the two-dimensional spatial distribution of the data storage structure, the encryption efficiency of traditional encryption method is very low, so a new encryption method suitable for image is needed to improve the encryption efficiency. Based on the commonality between chaotic mapping and encryption system, for example, the properties of chaotic topology transfer and aliasing are similar to those of cryptography, and the sensitivity of chaos to parameters corresponds to the sensitivity of cryptography to the key. Chaotic maps obtain exponentially separated orbits through multiple iterations, while encryption systems scramble clear text by scrambling and replacing multiple wheels. The main work of this paper is as follows: firstly, the basic concepts of cryptography and chaos theory are introduced, which lays a foundation for the research of image encryption methods based on chaos theory. The mathematical model of optical interference, Fresnel diffraction and Fourier transform of lens is described, which provides a theoretical basis for the virtual optical encryption system based on chaos theory. Secondly, a binary digital image encryption method based on Logistic chaotic mapping is proposed. Each pixel value of gray image is represented by eight bits binary number, and the two dimensional gray image is transformed into one dimensional digital string of 0 and 1 to process. According to the given initial value, the chaotic sequence is sorted by Logistic map and chaotic sequence is generated, then the location index is obtained, and the bit-level scrambling operation of the original image is carried out according to the location index. The result of image encryption can be achieved by integrating pixel fusion and pixel scrambling. Then, a new color image encryption algorithm based on Lorenz chaotic system is proposed. Aiming at the three components of color digital image, we encrypt the chaotic sequences of the three dimensions of the Lorenz chaotic system, and combine them into one at last. When encrypting, the pixel value of each decimal is regarded as an eight-digit binary number, and the ascending position index of chaotic sequence is used to scramble to achieve the purpose of pixel fusion and realize image encryption. Finally, a chaotic virtual optical imaging encryption system is proposed by unifying the chaotic system and the virtual optical system. The chaotic sequences are used to generate random phase templates and random amplitude templates, and then to modulate them jointly. Compared with traditional random templates, using chaotic sequences to generate random templates can reduce the volume of keys and improve encryption efficiency.
【学位授予单位】：南京理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TP309.7;TP391.41

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