【作者】 杨欣；

【导师】 黄席樾；

【作者基本信息】 重庆大学 ， 控制理论与控制工程， 2008， 博士

【摘要】 现在是计算机深入普及的信息时代,信息的传输通道是脆弱的公共信道,信息储存于“不设防”的计算机系统中,如何保护信息的安全使之不被窃取及不至于被篡改或破坏,已成为当今普遍关注的重大问题。当今,计算机技术发展迅速,运算部件处理数据速度越来越快,使得攻击者对密码的破译速度及成本也越来越少。因此实用、经济和安全度高的信息安全系统是信息时代的热点研究问题之一。混沌现象是在非线性动力系统中出现的确定性的、类似随机的过程,从80年代末,混沌开始被应用于保密通信领域,其中尤其受密码学界重视的是混沌序列密码方法。用混沌系统产生的密钥序列不仅表现出许多优良的密码学性能,而且混沌加密方法能极大地简化传统序列密码的设计过程。所以,混沌密码学方法是现代信息安全的重要研究前沿。本论文在对密码学理论和混沌理论的研究基础上,利用混沌序列的可重现性、随机性和初始值敏感性,把混沌映射与密码学理论相结合,构造设计信息安全系统,以保障信息的安全。本论文的主要研究成果包括:①对混沌的发展现状作了详细的论述,给出了混沌的多种定义,描述了混沌的非线性动力学特性,并阐述了混沌的判定准则和通向混沌的道路。通过对混沌理论的研究、分析,指出混沌理论可以应用于信息安全系统中保障信息的安全。②对混沌映射中“一次一密乱码本”加密算法进行了安全分析,指出虽然“一次一密乱码本”是唯一可在数学上证明其安全性的加密算法,但是,由于计算精度的限制,使得密钥流出现周期现象而降低了加密算法的安全性。针对这个问题,本文设计了一种参数μ动态累加产生器对密钥流发生器进行周期扩展,并分析了动态累加器的原理,构造了动态累加器的数学模型,避免了密钥流发生器在明文较长而计算精度较低的情况下出现重复使用密钥流的情况。通过性能分析,改进后的密钥流发生器的周期得到了很好的扩展,保证了一次一密加密的安全性。③对混沌序列的安全性进行了分析,指出混沌序列由于精度限制而发生伪随机性的现象会极大降低信息安全系统的安全度。针对这个问题,本文提出利用神经网络的非线性动力学特性对伪随机混沌序列实行进一步的混淆和扩散。在建立神经网络模型的过程中,为了避免混沌神经网络在较弱的激发强度下会陷入局部极小值,本文提出通过建立非线性前馈通道方法改进混沌神经网络。通过加密试验和安全性分析,表明伪随机混沌序列经过神经网络处理后,具有更好的随机特性。④对分组密码理论的安全性和混沌理论应用于分组密码的可行性进行了分析,指出由于传统分组密码中S-box的是一种静态结构且与密钥无关,而降低了加密算法的安全度。针对这个问题,本文提出应用双向混沌映射构造分组密码中最关键的S-box,通过实验分析,可见此S-box具有极好的动态随机特性,且与加密过程相关,具有密码学意义,极大的提高了加密系统的抗攻击能力。最后对全文的研究工作进行了总结,并指出了基于混沌理论的信息安全系统的进一步研究的方向。更多还原

【Abstract】 Today computers are used everywherer, and the information are transported in public channel. Then how to insure the information safe and integrated become more and more important than before. Nowadays, the computer technology develop rapidly and the operation-speed of computing components become faster and faster. So attacker can translate the cryptograph successfully within less time and cost. Thus the study of information security system is a popular subject in this information era.The phenomena of chaos is a determinate and random process in non-linear dynamics system. From 80’, the chaos was used in secrecy systems, specially in chaos-sequence encryption. The secret-key generated by chaotic system show the excellent characteristic of cryptology. and this method can predigest the traditional design course. So chaotic encryption is a important cryptology in modern information security system.This dissertation is based on the theory of cryptology and chaos. And this dissertation used the characteristic of chaotic sequence and combined chaotic map and encryption theory to construct information scurity system. The main achievements and originalities in this dissertation are as follows:①This dissertation discuss the development status in quo of chaos, set forth the different definiens of chaos, describe the non-linear dynamics characteristic of chaos, and expound judgment rule of chaos. This dissertation also indicate the chaos theory can be used in information security system via the studying, analyzing of chaos theory.②The security of traditional one-tine-pad cryptosystem is analyzed, and point out that the limit of computing speed should reduce the security though the one-tine-pad cryptosystem is the only one security encryption can be proved by mathematic technique. Thus,some issues which should be considered are presented.This dissertation applyμ-generator to expand the periods of secret-key, and analyse the elements and structure ofμ-generator . The security analyses prove this method can enlarge space of the secret-key, and ensure the security of ciphertext.③The security of chaotic sequence is analyzed, and point out that the chaotic sequence would appear the pseudrandomicity when there have no enough iterative precision. To solve this problem, this dissertation use non-linear dynamics characteristic of neural network to implement diffusing and mixing of sequence, and construct a neural network with forefeedback channels to avoid the chaos neural network get into infinitesimal. The security analyses and the experiment prove the secret key dealed with the neural neywork has good randomocity.④The security of block cryptosystem and the feasibility of using chaotic theory in block cryptosystem are analyzed, and point out that the traditional S-box in block cryptosystem is static and irrespective with encryption process. To solve this problem, this dissertation applied bidirectional chaotic map to construct S-box. The analyses and the experiment prove this S-box is dynamic, random and has good cryptological characteristic. The system can resist outer attack impactfully.Finally, the research works of this dissertation are summarized, and the future developing directions are indicated.更多还原