【作者】 俞飞宇；

【导师】 周祖德；

【作者基本信息】 武汉理工大学 ， 通信与信息系统， 2010， 硕士

【摘要】 随着计算机网络技术和多媒体信息技术的飞速发展,信息安全问题也随之而来。如何保证多媒体信息的真实性和完整性是急需解决的问题。数字水印技术作为信息隐藏技术的重要分支,在解决版权保护、媒体内容真实性和完整性认证方面有着良好的效果。在图像信息安全领域,脆弱数字水印技术在图像内容的真实性和完整性认证方面有着巨大的优势。本文介绍了数字水印算法的数学模型、特点和水印性能的评价标准,以及图像置乱技术在数字水印中的应用和可用于图像置乱的亚仿射变换,着重分析了亚放射变换的特点及其在图像置乱中的应用,研究提出了一种基于图像置乱的LSB脆弱水印算法,对原始图像和水印图像都进行了亚仿射置乱变换,能够较好的隐藏图像特征信息,同时把变换次数作为密钥保存。算法易于实现,安全性高。研究了离散余弦变换(DCT)在图像处理中的应用以及Hash函数和RSA加密算法,提出了一种将图像的特征信息作为水印信号的脆弱水印算法。图像进行分块之后,对图像块进行离散余弦变换,将变换系数作为图像的特征信息,利用Hash函数和RSA加密算法加密得到图像块的水印信号。由于每幅图像的水印信息都是从原图的特征中提取的,所以不同的图像嵌入的水印都是不同的,同时也不需要为水印信息开辟存储空间。水印信息的特定来源和加密过程提高了算法的安全性,图像的分块为篡改定位提供了良好的条件。研究了小波变换的提升算法和混沌序列在密钥中的应用,提出了一种基于整数小波变换和混沌序列的脆弱水印算法。图像变换使用了整数到整数映射的小波提升算法,在重构时能够实现图像的无失真变换。水印信息嵌入到小波系数的高频系数中,嵌入位置由混沌序列和小波系数的四叉树结构决定,保证了算法的复杂性和安全性。本算法具有较高的脆弱性,能够使用到要求较高的医学图像和法庭举证中。更多还原

【Abstract】 The rapid development of computer network technology and digital multi-media technology has brought about a slew of issues with regard to information security. The fact that digital products can be easily altered, pirated and illicitly distributed has confronted us with a new set of challenges. The verification of the integrity and authenticity of digital products is a problem that must be solved and it must be solved now. As an important branch of information hiding, digital watermarking technology has played an irreplaceable role in resolving IPR disputes and verifying the integrity and authenticity of digital products. Fragile watermarking, as part of the digital watermarking technology, is an academic hotspot for researchers and scholars around the world. An in-depth analysis of fragile watermarking technology is presented in this document.After briefly exploring the existing theories and algorithms about digital watermarking, image scrambling techniques are introduced in this thesis. The advantages and disadvantages of Asia affine transform are analyzed and a fragile watermarking algorithm based on LSB and image scrambling is presented in this paper. Since both the original image and watermark image in the algorithm were scrambled, a high level of invisibility of the watermark image is achieved. Furthermore, the number of Asia affine transforms applied to both watermark image and original image is regarded as the private key, which has improved the security of the whole algorithm.The second fragile watermarking algorithm proposed in this paper based on DCT and RSA, in which the features extracted from the original image is used as the watermark signal. First the original image is divided into blocks of predetermined size and DCT is applied to each and every block. DCT coefficients are viewed as the image feature and watermark signal can be obtained by applying Hash function and RSA cryptographic technique to the extracted feature, namely the DCT coefficients. Since the watermark signal is obtained from the original image, the proposed algorithm is self-adaptive and no extra memory is required for watermark information. The source of watermark signal and the encrypting processing have significantly enhanced the security of the algorithm and the dividing of the original image is very effective for tampering localization.After exploring the foundmentals of wavelet transform, lifting technique of wavelet transform and chaotic sequence, a novel fragile watermarking technique based on integer wavelet transform and chaotic sequence was presented in this document. The watermarking embedding process was determined by chaotic sequence and coefficients of integer wavelet transform. By so doing, the complexity and security of the proposed scheme have been substantially improved. Theoretical analysis and experimental results both show that the proposed scheme is highly fragile to changes to the watermarked image. Moreover, the medical and forensic applications of the proposed algorithm are also explored in this thesis.更多还原