基于PDF格式的数字版权保护算法

针对互联网中多渠道信息传播导致的文档篡改和所有权归属等问题。通过分析PDF文档结构及内容流特性,文中提出一种基于文本格式的新型算法。设计使用Kerckhoffs安全性准则和数字签名算法,以解决版权归属难题,并能有效甄别文档篡改。文中将不可见水印作为便携式数字签名嵌入PDF文档中,依据PDF文档结构中内容流的字体渲染模式和字体饱和度的可修改特性,通过选择性的修改和添加相关属性,在不损坏文档结构的基础上达到嵌入水印文本的目的。通过从PDF文档中提取出的水印,与原始水印的一致性检测,来辨别文档的真伪及版权归属。实验结果表明,该算法具有良好的透明性和鲁棒性,以及较大地水印容量,能进行篡改判别。

Digital Watermarking Protection Algorithm Based on Format of PDF Document

In order to solve the problems like document tampering that is leaded by multi-channel information dissemination on the Internet and the copyright of documents,this paper proposes a new algorithm that is based on the text format by analyzing the structure and content flow characteristics of PDF (Portable Document Format).The Kerckhoffs safety criteria and the digital signature algorithm are adopted to solve the problem of the copyright and to identify document tampering effectively.The author put the invisible watermark in the PDF document as a portable digital signature,thus modifying the properties of saturation without damage to the structure of the document through selective modification and adding related attributes to achieve the purpose of putting watermark in the document.Checking the watermark from the PDF document and the comparison with the original watermark can identify both the authenticity of a document and the copyright.The experimental result shows that the algorithm has good transparency and robustness,and has a larger capacity of watermark,which helps identify if the document has been tampered.