论文总字数：43712字

目 录

1 绪论 1

1.1课题研究背景与意义 1

1.2国内外研究状况 1

1.3本文研究的主要内容 2

2 混沌密码与混沌图像加密技术基础 2

2.1混沌理论 2

2.1.1混沌定义 2

2.1.2混沌系统的相关特性 3

2.2混沌密码理论 4

2.2.1混沌密码基本概念 4

2.2.2加密系统结构 4

2.2.3密码分析攻击分类 5

2.2.4混沌理论与密码学之间的关系 5

2.3图像加密相关知识 6

2.3.1图像加密概念 6

2.3.2基于混沌的图像加密技术 6

2.4图像加密置乱算法和扩散算法基本理论 7

2.4.1图像加密置乱算法 7

2.4.2图像加密扩散算法 8

2.5混沌加密性能评价指标 9

2.5.1图像加密/解密速度 9

2.5.2密匙空间 10

2.5.3密文统计特性 10

2.5.4图像分析 10

2.5.5信息熵 11

2.6图像密码系统的敏感性分析方法 11

2.6.1密钥敏感性分析 12

2.6.2明文敏感性分析 12

2.6.3密文敏感性分析 12

3 明文关联混沌图像密码系统构建及其Matlab仿真 13

3.1典型混沌图像加密系统 13

3.2一种基于分段线性映射的明文关联混沌图像密码系统 14

3.3该系统的图像加密与解密方案 14

3.3.1混沌密码发生器 15

3.3.2明文无关的前向扩散模块 15

3.3.3明文关联的置乱模块 15

3.3.4明文无关的后向扩散模块 16

3.4Matlab仿真过程与结果 16

4 明文关联的混沌图像密码系统性能测试 18

4.1加密与解密速度测试 18

4.2密钥空间测试 18

4.3信息熵测试 19

4.4密文统计特性测试 19

4.5密钥敏感性测试 22

4.6明文敏感性测试 24

4.7密文敏感性测试 26

4.8明文关联置乱图像密码系统性能评价 28

5 总结与展望 28

5.1总结 28

5.2展望 28

参考文献 29

致谢 30

附录 31

基于混沌的数字图像加密及性能研究

方思民

, China

Abstract:

With the rapid development of Internet technology, multimedia applications are becoming more and more widespread. Digital images play an important role in the field of multimedia information. Digital images can convey intuitively rich information. The Internet is an open platform. Transmitting digital images on the Internet is vulnerable to security problems such as tampering and theft. In the increasingly prominent situation of Internet security threats, the most direct and effective method for securing digital images in network transmission is to encrypt digital images.

This article is mainly divided into three parts:

The first part mainly studies related theories, including chaos theory, cryptography theory, image encryption scrambling algorithm and diffusion algorithm, performance evaluation method of chaotic digital image cryptography system. Using Matlab, the image was scrambled and column scrambled to achieve a typical image encryption.

The second part first introduces a typical chaotic image encryption system. Considering that the password of a typical image cryptosystem is only related to the key, it has nothing to do with plaintext and is vulnerable to the choice of plaintext attack or known plaintext attack. After referring to the traditional plaintext association encryption algorithm that is related to both the key and the plaintext image, this paper uses the plaintext-independent diffusion algorithm and the plaintext associated scrambling algorithm, and uses piecewise linear in the chaotic cipher generator. The chaotic map (PWLCM) replaces the traditional hyperchaotic Lorenz system mapping, and a new piecewise linear mapping-based plaintext relational chaotic image cryptosystem is constructed. The algorithm is used to encrypt and decrypt images using Matlab simulation.

The third part uses Matlab software to test the algorithm's encryption and decryption speed, key space, and information entropy first, and then tests the statistical characteristics of the ciphertext from the histogram, c2 test results, and correlation coefficients, and then passes Gaussian, salt and pepper, and The attack was cropped, and the NPCR, UACI and BACI values were analyzed and calculated. The key sensitivity, the plaintext sensitivity and the ciphertext sensitivity of the algorithm were tested. The results show that the algorithm has fast encryption and decryption speed, large key space, close to ideal information entropy, good ciphertext statistics, strong key sensitivity, plaintext sensitivity, and ciphertext sensitivity. The algorithm has good performance and can resist various attacks.

Key words: Chaos; Digital Image Encryption; Plaintext Correlation; Security Performance

1 绪论

1.1课题研究背景与意义

随着社会的进步和人类的发展，人类社会信息化速度十分惊人，互联网信息技术推动人类社会变革和发展，人们的工作、生活以及学习等方方面面有了很大的变化，如今的社会是一个高度信息化的社会。在互联网数字多媒体中，数字图像包含的信息十分丰富、逼真、形象，是人们获得信息、传输信息进行日常交流的主要方式之一。在人们每天的日常交流中，会在网络上进行传输大量的数据图像信息，互联网技术让人们的生活更加便捷更加丰富多彩，但是便利多彩的网络生活中却存在很多安全隐患威胁。互联网是开放的网络，存在着许多不确定的安全因素，在图像数据传输过程中，可能会被恶意的篡改、窃取以及非法复制等。所以，如何保证图像的安全显得十分重要，国内外专家学者十分重视对图像加密有关技术的研究。

传统的分组加密算法，例如：高级加密标准，对图像加密来说并不适用，原因是这些算法都是针对于文本进行加密的算法。数据量大、冗余度高、能量分布不均匀以及相邻像素相关性高是图像信息的特征，这些特征导致了传统分组加密算法对数字图像加密效率十分低。在当前信息安全领域中，有很多技术方法用于实现对数字图像进行加密。例如：基于混沌的数字图像加密技术和基于矩阵变换的数字图像加密技术等。但是，传统的图像加密技术，例如，分形曲线扫描技术等，只是对图像像素位置进行置乱，图像的像素值并没有改变，攻击者可以通过图像灰度直方图分布等统计特性或者穷举法破解密文图像。因此，传统图像加密算法面对各种攻击显得比较脆弱。

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