【作者】 赵亮；

【导师】 廖晓峰；

【作者基本信息】 重庆大学 ， 计算机系统结构， 2009， 硕士

【摘要】 近年来,计算机技术和网络技术得到了充分的发展,随之而来的是多媒体信息被人们广泛地应用到社会的各个领域。正因为如此,多媒体通信中的安全问题日益成为了人们的焦点,而密码学是解决多媒体安全的关键技术。与普通的文本数据不同,多媒体信息数据量非常庞大,如果采用传统的加密方式则需要消耗大量的计算资源和能量,而在多媒体信息中又以数字图像信息应用最为广泛,并且也可以很好的将其应用方式推广到其他的多媒体格式,因此,本论文以研究数字图像的加密为主要内容。由于最近几年来,基于非线性科学的数字混沌理论在图像加密中得到了广泛的研究,特别是混沌所具有的特性使得其非常适合于图像的加密,所以,本论文主要研究在保证安全性的条件下,如何利用数字混沌技术分析和设计新颖的图像加密算法,本论文的主要工作包括以下几个部分:①简述了混沌理论以及基于混沌的图像加密算法。从多个方面对混沌理论基础作了详细的论述,同时,介绍了密码学中的几个基本概念,然后对比了两者之间的关系,最后分别介绍了几种现有的混沌图像加密方法以及对应的算法。②对孙福艳等人所提出的基于混沌系统的图像加密算法进行了有效的改进。首先对该算法做了统一的描述,然后提出了它的三个主要安全隐患。在此基础上,提出了一个改进的算法,并对其进行了安全性和效率测试。③提出了一种高维Z-矩阵的映射。通过把所设计的高维Z-矩阵映射和现有的几种图像加密映射进行分析比较,可以发现所提出的矩阵映射具有周期长和对于不同维数具有不同周期数等良好的特性,因此该矩阵映射可以很好的应用在图像加密中。④针对所提出的高维Z-矩阵映射,分别将其应用在了图像保密加密和图像退化加密中。对于图像保密加密,提出了一种基于Z-矩阵映射和PDP模式的图像加密算法,并从理论和实验上证明了该加密算法具有良好的密码学特性;而对于图像退化加密,本文提出了两种基于不同模板方式(基于随机选择模板和基于信息熵划分)的退化加密算法,然后利用实验和比较分析了所提出的退化算法具有的实际应用前景。最后对全文进行了总结,并指出了本论文的不足之处以及今后进一步研究的方向。更多还原

【Abstract】 With the development of computing and network technologies, multimedia information is used in many fields more widely. As a result, the security of multimedia information becomes increasingly important and cryptography is considered as the primary method to resolve it. Contrast to common texts, multimedia contents usually contain huge volume of data, which makes their encryption become very slow and power-consuming with the traditional cryptosystem. Furthermore, the digital image information is the main content of multimedia information and the applications of it can spread to other multimedia formats effectively. Therefore, the main research of this dissertation is based on digital image encryption. During these years, as the merits of chaos are suitable for image encryption, the image encryption based on chaos which comes from nonlinear science is studied widely. This paper focuses on analyzing and designing the novel image encryption schemes based on chaos, under the condition that those approaches satisfy the security requirements. The main contents of this paper are listed as follows.①Chaos theory and chaotic image encryption algorithms are introduced. The chaos theory is described from multiple fields in details. At the same time, the concept of the art in modern cryptography is stated. Then, the relationship between them is compared. Finally, same chaotic image encryption methods and algorithms are recommended, respectively.②The image cryptosystem proposed by Sun Fu-Yan et al. is improved effectively. First, a generalized description of Sun Fu-Yan’s cryptosystem is given. Then, three inherent weaknesses of their algorithm are presented. Based on these analyses, an improved image encryption scheme is proposed, and some tests about security and effect are carried out.③A multi-dimensional matrix map named Z-matrix map is proposed. Compared with some maps which are used for image encryption, it is found that the proposed Z-matrix map has some favorable characters including long period and different period with different dimension. Therefore, this matrix map is more suitable for image encryption.④Based on the proposed Z-matrix map, two different image encryption schemes including confidentiality encryption and degradation encryption are presented. For the confidentiality encryption, a new image encryption algorithm based on Z-matrix map and PDP model is introduced. Some merits of this scheme is also analyzed and tested; For the degradation encryption, two different templates (random selective template and entropy dividing) are used in degradation scheme. The theory analysis and experimental tests demonstrate the prospects for practical application.Finally, the dissertation is concluded. Some problems as well as further work are also given.更多还原