【作者】 刘东；

【导师】 周明天；

【作者基本信息】 电子科技大学 ， 计算机应用技术， 2008， 博士

【摘要】 近年来,随着以互联网技术为代表的信息技术的迅猛发展,各种文字、图像、声音、视频等媒体的获取、保存与使用方式发生了很大的变化。这一方面给人们带来了极大的方便,但另一方面,未经版权所有人许可对数字作品的任意复制、修改等盗版行为也日趋严重。因此,如何在互联网环境下进行有效的版权保护等信息安全问题,也就成为了重要的研究课题。在此背景下,数字水印技术作为一种新的多媒体信息安全保护技术应运而生。它将隐藏信息嵌入到各种数字媒体中,结合传统的数据加密技术来实现信息的隐藏通信、访问控制、版权保护等功能,当前,该领域的研究与应用已经相当深入。但令人遗憾的是,由于文字媒体本身的一些特点,作为数字水印技术重要组成部分的文本数字水印技术的进展却是相对滞后的,这与文字是人类传播信息最主要方式的现实情况形成了很大的反差。本文的工作就是要针对现有文本数字水印技术存在的薄弱环节,进行新型的文本数字水印技术及其典型应用的研究。主要的研究内容涉及文本数字水印嵌入算法、水印检测方法、系统实现框架、抗攻击技术及典型应用等该领域的关键问题,取得了如下创新性成果:1)提出了一种基于字符拓扑结构的文本数字水印技术,通过改变字符或者字符串字形的拓扑结构,设计出语义上相同的字符(串)的多种字形,并对这些字形的拓扑结构进行恰当的编码,利用字符(串)的拓扑结构来携带数字水印信息。同时,给出了鲁棒性和视觉影响试验方法、结果,并分析了水印的抗攻击性能。2)引入图论作为1)所述的文本数字水印技术的数学基础,将字符字形映射为图论中的“图”,对“图”或者“图”的特征量进行恰当的编码,利用这些编码来表示数字水印。同时,给出了基于图论的水印嵌入、检测方法的数学模型和详细实现过程。3)提出了一种以符号的冗余编码表示隐藏信息的隐藏数据通信技术,以及与该方法相关的文本数字水印嵌入、检测技术和载体文件的显示技术。这些技术包括:将符号编码成冗余数字代码的若干方法;隐藏通信的数据加载与分离方法;特定字体文件的设计方法;若干对嵌入水印信息的载体文件进行显示的方法。在此基础上,利用冗余编码的原理,还提出了一种利用索引值嵌入隐藏信息的图像数字水印算法。4)结合基于“字符拓扑结构”和“冗余编码”的文本数字水印技术的特点,提出了文本数字水印系统完整解决方案。给出了两种特殊的字体设计方法,重点描述了在统一的框架体系中,实现在电子文件和印刷品文件上嵌入、检测数字水印的技术。5)提出了一种新的隐藏通信方法,其原理是改变字符图形与字符编码在各种编码标准规范中已确定的标准映射关系,采用自定义的方法进行字符图形与字符编码的映射,从而使得电子文件显示出的字符图形与电子文件的内在编码分别构成显式通信信道和隐藏通信信道,这两种信道可以独立地进行通信。应用该隐藏通信技术制作成自包含字符图形和编码信息的电子文件,便于利用现有互联网搜索引擎按照文件的属性进行在线搜索。6)针对同步攻击这一困扰扩频水印技术的难题,研究了一类基于字符特征的文本数字水印技术的编码映射规则,给出了相应的扩频水印加载与检测模型。利用字符语义在水印加载与检测过程中具备的良好鲁棒性,通过载体字符产生伪随机代码,最终生成具有同步错误修正能力的自适应扩频文本水印,仿真实验表明其抗同步攻击性能得到了显著的提高。7)提出了一种新的数字内容网络出版发行机制,其主要特点是用户可免费获取数字内容,但必须强制性地观看广告,广告与数字产品关联绑定。描述了这种机制的系统体系结构及相关技术协议,给出了实现该机制所需的内容加密、水印嵌入、屏幕字符替换等关键技术。该机制为平衡数字内容价值链中各方的利益提供了一种新的解决途径。更多还原

【Abstract】 In recent years, with the development of information technologies, especially the popularization of Internet, the acquirement, storage and application means of different multimedia such as text, image, music and video have changed greatly. On the one hand, those changes bring us so many conveniences, On the other hand, they also make a great deal of trouble, people can copy and tamper digital products more easily without permission of their copyright owners. Therefore, the problems of information security such as how to protect the copyright effectively on Internet become urgent research subjects.Under this condition, the digital watermarking technology, as a new approach which is applied to protect security of multimedia products, comes into being. It can protect the intellect property of copyright owners by embedding hiding informations into digital multimedia products. Digital watermarking technology, combining with traditional encryption technology, can also carry out the functions such as secret communication, access control and digital rights protection etc. At present, the researchs and applications of digital image watermarking technology have already become maturity day by day. But as an important part of watermarking field, the text watermarking develops slowly, because of the generic characteristics of text media. This situation contrasts clearly with the fact that texts are the most popular communication intermedium for us.This dissertation aims to research the key issues in both theories and applications of the text watermarking technology, including watermarking embedding algorithms, detecting algorithms, system framework, anti-attacking techniques and critical application mode ,etc. The main contents are as follows:1) A novel text digital watermarking technology based on topology of characters or strings is presented. Through changing the topology of a character or string, different structure figures are schemed out, which represent the same semanteme, and these figures should be correctly encoded. With this technology, digital watermarking informations are embedded in different topology of a character or string.2) Graph theory is applied to be the mathematic foundation of text digital watermarking technology, which is described in 1). Figures of characters or strings are mapped on graphs in Graph Theory, and the graphs or their properties should be correctly encoded in order to denote the text watermarking information. Furthermore, the mathematic models of embedding and detecting watermarking are also described, as well as the isomorphic algorithm of graph.3) A hiding information communication technology based on storing hiding information in redundant codes of symbol is proposed, as well as associated methods of embedding, detecting watermark and showing files in which watermark is embedded. The relational technologies include: encoding Symbol, loading /separating hiding information on/from carrier file, designing the special font library, showing files in which watermark is embedded. Furthermore, according to the theory of redundant-coding, an image watermark algorithm which applies the index of an image to carry hiding information is presented.4) Applied to the watermarking technologies based on topologies and redundant codes of alphabetic symbols which are described in 1) and 3), an integrated solution for text digital watermarking system is proposed. Furthermore, the united framework and the methods of designing two special font libraries are emphasized. This integrative system is suitable to embed and detect watermark in both electronic and print files.5) A new method of hiding information communication is proposed. That is to create user-defined mapping relationship between a character figure and its inner code, instead of standard-defined mapping in different criterions. So character figures in electronic files constitute the apparent communication channel while inner codes constitute the hiding communication channel, and the two channels can work independently. If the technology is particularly used to make electronic files which themselves include both character figures and inner codes, the files can be found by current Internet search engines, according to the properties of the files.6) Synchronization attack is an intractable problem in the spread-spectrum digital watermarking field. To deal with it, the encode-mapping rule of a type of text digital watermark based on symbolic characteristics is proposed, as well as it’s embedding and detecting modes of spread-spectrum watermarking. With the excellent robustness of symbolic semanteme during embedding and detecting processes, pseudo-random sequences are generated by carrier symbols of watermarking. Then the adaptive spread-spectrum text digital watermarking which can rectify errors of synchronization is finally created. The experiments show that the spread spectrum watermarking system’s performance resisting to synchronization attack is obviously improved.7) A novel network publishing mechanism of digital contents is proposed. Readers using the system can get and read digital contents free of charge, but should be forced to browse advertisements which are bound with digital contents. The architecture of the mechanism and the related protocols are described, as well as the key technologies of the mechanism, such as methods of encrypting, algorithms of embedding/detecting watermark and techniques of replacing character on monitor, etc. This mechanism provides a new solution for balancing profits of different entities in the digital content value chain.更多还原