Research On Novel Text Digital Watermarking Technologies And Their Typical Applications

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.