【作者】 吴悠；

【导师】 孙星明；

【作者基本信息】 湖南大学 ， 计算机软件与理论， 2005， 硕士

【摘要】 互联网在当今社会中的广泛应用,极大地便利了信息的分发与获取。但是,如果缺乏有效的措施来预防对数字信息内容的复制与传播,版权信息是极易被侵犯的。数字水印技术被认为是解决这一问题的有效途径。目前,在这一领域已有不少研究,但是,与针对于图像、音频、视频等方面的研究相比,对以文本文档为载体的数字水印研究较少,这是由文本文档结构上的特殊性决定的。而且英文和汉字在空间特征和语义上均存在差异,需要根据汉语文本的特征提出相应的水印算法。本文基于正弦波的相关理论,根据文本数字水印的不同应用领域,对中文数字水印技术进行了深入的研究。一方面保留微调文本格式的思想,利用正弦函数控制字符的灰度值;另一方面在水印嵌入时,结合了中文文本的结构信息和汉字信息。本文所做的工作分为三个方面:首先,提出了一种用于文档认证的水印算法,以保证文档的真实性和完整性。即将原始文本按段落分成多个相对独立的块,由与该块相关的文本特性决定正弦波的参数,然后通过改变块内字符的灰度值,嵌入对应的正弦波;其次,提出了一种用于版权标识的水印算法,将版权信息嵌入文本,保护其所有者的权益。即将版权信息加密成二进制序列,重复嵌入文本中,水印嵌入的强度由用户决定。同时为了提高水印的鲁棒性,结合汉字数学表达式的二叉树理论对文本进行随机嵌入,并采用正弦波来控制灰度值的改变量,分隔不同段的水印信息,在水印提取时起到降低误码率的作用;最后,提出了一种用于分发控制的水印算法,防止未授权的文本拷贝,追踪非法用户。即通过用户信息注册,产生与文本对应的一个伪随机序列号,加入CRC纠错码后,形成水印序列。嵌入时,只对汉字频率表中排前1000位的高频字进行嵌入,其灰度值的改变量由正弦函数决定。正弦函数的相关参数仅与该汉字的字频信息有关,与其在文本中的出现位置无关,因此大幅度地提高了水印的鲁棒性。提取时通过查找数据库,将提取出来的二进制水印序列对应到数据库中的用户信息。实验证明,利用以上算法嵌入水印的文本具有较好的透明性,而且三种算法在各自的领域均具有一定的应用价值。更多还原

【Abstract】 With the wide spread use of the Internet in our society, the distribution and access of information is greatly facilitated. However, without effective methods which can prevent illicit redistribution and reproduction of information content, copyright can be easily infringed. Digital watermarking is widely believed to be a valid solution to the problem. Currently, there is intensive research in this area. However, compared to the plurality of previously proposed methods in digital watermarking for picture, audio and video, digital watermarking methods for text documents are very limited. One reason for this difference is the special features of text documents structure. Moreover, Chinese is differing with English in both spatial characteristic and semantics, thus we should present corresponding watermarking methods of Chinese text document according to its characteristic.This paper performs an in-depth research on Chinese digital text watermarking in different application fields, which is based on the sine wave theory. On the one hand, the idea of watermarking is used by slightly adjusting text format, which changes the grayscale of characters by sine function; on the other hand, the algorithm considers the structure of Chinese document and information of Chinese character during the embedding. The study can be concluded into three aspects: Firstly, a scheme for document authentication is proposed, which can ensure the authenticity and integrity of text. The method segments the original document into paragraphs and determines the parameters of sine wave by the characteristic of related text block. Then the watermark can be embedded. After the modification, the alteration of the grayscale shows characteristics of corresponding sine wave; next, a scheme for copyright marking is proposed, which embeds the copyright information into the text document to provide protection. The method encrypts the copyright information into binary sequence for repeated embedding and the intensity of watermarking can be set by the user. At the same time, it introduces the binary-tree theory of Chinese Mathematical Expression during the random embedding to improve the robustness of watermarking. The alterations of grayscale is also controlled by sine wave, which can divide the mark into several segments and reduce the error rate in the detection; lastly, a scheme for distribution control is proposed, which can prevent unauthorized document copy and trace the unlawful user. The method generates a random sequence to identify the original recipient of the document by user register. Then it uses the CRC error coding technique to form a watermark sequence. Only characters which rank first 1000 in the更多还原