【作者】 车生兵；

【导师】 傅明；

【作者基本信息】 长沙理工大学 ， 计算机应用技术， 2004， 硕士

【摘要】 基于混沌的数字图像加密算法中,序列流式加密算法是主流研究方向。目前的算法生成的密文只与生成的密码序列值相关,是由一个密钥决定的从明文空间到密文空间的可逆变换,虽然有些算法致力于研究新的、更复杂的混沌动力系统函数,但仍然只是简单的空间映射,这些算法有的还自身存在设计缺陷,使用起来十分不方便。基于复合离散混沌动力系统的序列密码体系使复合迭代系统保持了所有迭代子系统的混沌特性,确保复合混沌迭代系统的行为比单个子系统的行为复杂得多。但在考虑双重混沌性的时候,在安全策略上仍无法在复合混沌动力系统被破译后,提供由计算机用户高度自主控制的附加安全保障。且在考虑选择复合离散混沌动力系统中子系统的混沌性时,忽略了线性反馈移位寄存器的长周期性,其理论证明也存在缺陷和错误,很有必要做一些改进。 本文主要是改进了一个基于复合离散混沌动力系统和小波变换的数字图像加密、解密体系。具体完成了小波变换融入、分离数字印签的算法;基于复合离散混沌动力系统的序列密码加密、解密算法;改进线性反馈移位寄存器;补充并纠正了一些算法证明。本文改进后的算法具有以下特点:多种防御措施,用户拥有加密与解密的自主控制权,易于追踪;有较大的密钥空间;算法运算过程不可逆,且复合混沌子系统的选择复杂,系统有良好的抗统计分析能力;具有更均匀分布的密文且对密钥非常敏感;明文每一bit与密文的若干bit有关,明文与密文的相关度低,复合离散混沌动力系统中子系统的选择更复杂。 从本文算法的多种密码体制的防御策略、较好的复合离散混沌动力系统和小波变换算法来看,算法的安全强度有所提高,用户自主控制数字图像加密、解密的手段更加灵活实用,算法的工作方式符合分布式计算机系统的工作方式。更多还原

【Abstract】 Encryption with stream cipher is the main arithmetic in digital image encryption based on chaos. Currently, almost all the algorithms are from plaintext to ciphertext relevant to generated stream cipher that controlled by the key. Though some algorithms study newer and more complicated chaotic functions, they are only mapping between spaces and some have self-designed bug that you can not use them expediently. Stream cipher algorithms based on composite nonlinear discrete chaotic dynamical systems keep all the chaotic characteristic of single iterations that it keeps composite nonlinear discrete chaotic dynamical systems more complicated than any other single chaotic system. But it also can not keep safety of information in strategy when the only defence is broken, especially can not give the owner highly control with self-determination, let alone additional security guarantee. And when selecting sub-system of chaotic systems, they ignored the long periodicity of linear feedback shift register (LFSR)and there is theoretical error and bug in their testify. This causes to give some improvement.The work of the paper is to perfect and set up a system of encryption and decryption algorithms based on composite nonlinear discrete chaotic dynamical systems. They are wavelet transformation fusing and getting rid of digital seal, encryption and decryption algorithms based on composite nonlinear discrete chaotic dynamical systems, improvement on LFSR. So the algorithms we suggest have more big key space, more systemic security, more uniformity of ciphertext and pretty much sensitive to key, ciphertext bit is confined to the next plaintext bit and selection of sub-system of chaotic functions is more complicated.From the view of the two level defence strategy and perfect composite nonlinear discrete chaotic dynamical systems and wavelet transformation, our algorithm has higher secure intensity, the owner can freely control the encryption and decryption of digital image, tally with the mode of the distributed computer systems, we can say that our algorithm is utility and has perfect applications.更多还原