LDPC码在混沌序列图像加密中的应用研究

发布时间：2018-01-05 02:14

本文关键词：LDPC码在混沌序列图像加密中的应用研究　出处：《烟台大学》2017年硕士论文　论文类型：学位论文

【摘要】：低密度奇偶校验码(Low Density Parity Check code,LDPC码)是一种线性分组码,其性能接近Shannon限,与其它译码算法相比,它的译码复杂度低,并且结构灵活,成为人们的研究热点。近些年来,LDPC码的编译码算法不断地被改善和提高,并且被广泛应用于深空通信、光纤通信、移动通信和水下等领域。在混沌图像加密中,通常是采用混沌序列单层映射加像素置乱来完成,由于有的混沌序列鲁棒性很差,在信道传输的过程中,很难保证信息在受到攻击破坏后还能还原出原来的有效信息,因此本文引入LDPC码,将其应用在混沌图像加密中,通过对图像进行分块编码形成差错保护,以提高图像传输过程中的稳定性,改善传输性能。综上所述,本文的主要做了如下研讨工作:首先介绍了LDPC码和混沌序列加密的发展研究现状,然后具体描述了LDPC码的理论知识,包括其表示方式、构造方法还有常见的编译码算法,重点分析了几种编码译码算法的原理。其次,简要介绍了密码体制,分析了几种常见的离散混沌映射系统,对LDPC码应用于Logistic混沌序列图像加密中的方案进行了详细介绍,提出了分块加密差分保护的方案,用MATLAB软件进行仿真,验证了这种方案是可行的。然后,利用FPGA实现了混沌序列图像加密方案的LDPC码译码器的设计,使用Verilog HDL语言,编写各个模块,给出译码器的整体结构图,深入研究了译码器中校验节点和变量节点处理过程,最后得出译码结果。最后,总结本文的研究工作,指出论文的不足之处,及未来研究方向。
[Abstract]:Low Density Parity Check code is a linear block code, and its performance is close to the Shannon limit. Compared with other decoding algorithms, its decoding complexity is low, and its structure is flexible, so it has become a research hotspot. In recent years, LDPC coding and decoding algorithms have been continuously improved and improved. And it is widely used in the fields of deep space communication, optical fiber communication, mobile communication and underwater. In chaotic image encryption, chaotic sequence monolayer mapping and pixel scrambling are usually used to complete the chaotic image encryption. Due to the poor robustness of some chaotic sequences, it is difficult to ensure that the information can restore the original effective information after the attack in the process of channel transmission, so the LDPC code is introduced in this paper. In order to improve the stability of image transmission and improve the transmission performance, it is used in chaotic image encryption to form error protection by block coding. The main work of this paper is as follows: firstly, the research status of LDPC code and chaotic sequence encryption is introduced, and then the theoretical knowledge of LDPC code is described in detail, including its representation. The construction method also has some common encoding and decoding algorithms. The principle of several coding and decoding algorithms is analyzed. Secondly, the cryptosystem is briefly introduced, and several common discrete chaotic mapping systems are analyzed. The scheme of LDPC code used in Logistic chaotic sequence image encryption is introduced in detail. The scheme of block encryption differential protection is proposed and simulated by MATLAB software. It is proved that this scheme is feasible. Then, the design of LDPC decoder of chaotic sequence image encryption scheme is realized by using FPGA, and each module is programmed by Verilog HDL language. The whole structure diagram of the decoder is given, and the processing process of check node and variable node in the decoder is deeply studied. Finally, the decoding results are obtained. Finally, the research work of this paper is summarized and the deficiencies of the thesis are pointed out. And the future research direction.
【学位授予单位】：烟台大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN911.22;TP309.7

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