【作者】 丁文霞；

【导师】 沈振康；

【作者基本信息】 国防科学技术大学 ， 信息与通信工程， 2008， 博士

【摘要】 随着计算机技术和网络技术的飞速发展,多媒体信息安全问题显得日益重要。由于多媒体数据本身具有高冗余性、数据量大等特点,因此对它的安全保护有着特殊要求,如:高实时性、自认证性和可用性等等。传统密码学对多媒体数据的保护不是十分有效。考虑到传统密码学的不足,近年来,人们开始寻求多媒体信息保护的新方法。其中,基于混沌的加密技术和数字水印技术显示出了其独到的优势,很有可能成为新的多媒体保护的有效手段。本文基于离散混沌的基本理论,对图像、视频等多媒体数据安全算法进行了系统的研究,主要内容包括:(1)在混沌理论方面,从混沌映射的基本特性出发,研究了离散混沌系统中周期化和有限精度等因素引起的混沌动力学退化现象,并从周期点角度证明了一维混沌动力学系统中平凡密钥和拟平凡密钥的“广泛”存在性,提出了相应的改进思路,并在此基础上提出了五种实用的质量较好的数字化混沌密钥流产生的改进方案,包括二进制混沌伪随机序列、N相混沌伪随机数序列及二维混沌密钥矩阵等。论文重点对离散混沌系统中的两类群结构进行了研究和证明,得出了定长混沌二值(或整数)序列对异或运算构成群和混沌一维置换序列和二维置换矩阵对置换变换构成置换群的结论,此结论对以“置乱”和“混迭”为核心的各类混沌加密算法的设计具有一定的理论指导意义。(2)在基于混沌分组密码的加密技术研究方面,针对数字图像加密,提出了一种基于可逆混沌映射的将“置乱”、“替换”和“混迭”等技术相结合的能够有效的抵抗诸如明文攻击、统计分析、差分攻击等攻击的数字图像分组加密改进算法;随后对离散二维Arnold变换的周期性现象进行了深入研究,提出了一种将二维Arnold变换和混沌矩阵置乱双重置乱相结合的周期性改进方案,并在此基础上提出了一种基于二维Arnold变换的空域数字图像加密改进算法;最后将二维可逆混沌映射扩展到了三维,提出了一种基于三维Arnold映射的DCT域彩色图像分组加密算法。实验证明,随着维数的增加,这些算法在加密速度和安全性上均有较大的提高。(3)在基于混沌序列密码的加密技术研究方面,针对MPEG-2视频流加密,提出了两种直接针对压缩后视频流数据的快速实用的改进算法,这些算法利用混沌序列密码良好的随机性和密钥敏感性,在保证了较高安全性的同时,极大的提高了算法的运算速度。随后提出了一种基于混沌的S-盒候选方案,并用其做替换操作,进一步提高了此类算法抵抗线性攻击和差分攻击的能力。(4)在基于混沌的数字水印技术研究方面,针对数字水印的特性要求和不同应用背景,利用混沌序列良好的初值敏感性、随机性、遍历性和庞大的密钥空间,分别提出了一种基于混沌的半脆弱数字水印算法和一种多功能数字水印算法。前者很好的实现了篡改检测和定位,而后者结合多种数字水印技术,较好的实现了完整性认证、篡改检测、版权认证等多种水印功能,同时拓展了混沌在数字水印方面的应用形式。最后论文分析了当前在混沌加密与数字水印研究中存在的问题,并指出了进一步的研究方向。更多还原

【Abstract】 With the development of computer technology and network communication, the protection of multimedia content in the context of information security has attracted more and more attentions in recent years. Due to the intrinsic properties of multimedia such as high redundancy and bulk capacity, peculiar attention should be paid to operation speed, self-authentication and noninterference of the availability of data, etc. The validity of multimedia protection can not be met by traditional cryptology due to the issues mentioned above.In consideration of the disadvantage of traditional cryptology, more effective approaches were studied and investigated to meet the requirement of multimedia protection, among which chaos based encryption and digital watermarking technology exhibit prospective advantage.In this dissertation, some issues on multimedia protection are studied and several discrete chaos based encryption schemes and multimedia watermarking algorithms are investigated as well, which are detailed as follows:(1) In the context of chaos theory research, the chaotic dynamical degeneration phenomena caused by the periodicity and finite precision of discrete chaotic system are studied firstly. The“wide”existence of the invalid-keys and the quasi invalid-keys are analysed by means of the existence periodic points in one dimensional chaotic dynamical system. Then five improved schemes of discrete chaotic key stream generation, which include binary chaotic pseudo-random, N-bit sequences and two-dimension chaotic matrix, are proposed based on the research above. Researches on the group properties in discrete chaotic system are the most significant part in this dissertation, from which it can be concluded that fixed chaos bit or integer sequences are XOR groups, and chaos permutation sequences and two-dimension permutation matrix are permutation groups. As the conclusion indicates, it can be guided to support the design of various encryption algorithms based on‘permuting’and‘mixing’.(2) Concerning the digital image encryption, an improved algorithm of chaotic block cipher for image encryption combined with‘permutation’,‘substitution’and‘mixing’is proposed to resist the plain text attack, statistic analysis and difference attack. Then an improved encrypt scheme based on two-dimensiones Arnold map and chaos permutation matrix is proposed on the researches of periodical phenomena on the two-dimensiones discrete Arnold map. A color image encryption scheme based on three-dimensiones Arnold map in DCT field is proposed by means of extending the dimension from two to three. The significant performance improvement is proved by cryptanalysis and experiments.(3) In the context of encryption schemes based on chaotic stream cipher, taking MPEG-2 video stream as main encryption objects, several improved algorithms and encryption schemes for compressed video stream are proposed to provide direct and fast encryption operation. The proposed entire-encryption algorithms utilize the outstanding randomicity and key sensitivity of chaotic stream cipher to provide high level security and enhance the algorithm operation speed simultaneous. Then a scheme candidate of designing S-box based on discrete chaotic system is introduced to process the substitution for improving the ability of resisting difference attack and linear attack.(4) Concerning with digital watermarking based on chaotic dynamical system, two algorithms are proposed by utilizing the advantages of chaotic sequence, which include the initial value’s sensitivity, randomicity, ergodicity and the bulkiness of key space. The proposed“half-fragile”digital watermarking algorithm can support detection and orientation of the modification, while the proposed multifunctional digital watermarking algorithm can provide various watermarking functions such as integrity authentication and copyright authentication. The application method of chaos system on digital watermarking has been expanded at the same time.Finally, the thesis is concluded by pointing out some open issues on the current research of chaos based encryption and digital watermarking as well as indicating further research directions.更多还原