Research On Webpage Fragile Watermarking Alforithm With Tamper Localization On The Browser

Along with the rapid development of computer network technology, browsing webpage has become an important way to achieve information. Since the webpage information is easily edited and rapidly spread in open network environment, the webpage information is vulnerably tampered. Therefore, the integrity and authenticity of the webpage protection has been a practical problem to be solved. This thesis which is about webpage fragile watermark with authentication studies the watermark insertion and tamper localization.This thesis firstly introduces digital watermarking and the significance of webpage digital watermarking. Then, the research background of webpage watermarking is analyzed from three aspects: watermark generation, watermark insertion and tamper location. The analysis could be considered as the basis of the proposed algorithms in this thesis.This thesis proposes a fragile webpage watermark scheme which could locate tampering on the browser. In the scheme, the webpage is firstly divided into webpage-blocks according to the labels which contain the displayed characters on the browser. For each webpage-block, the watermark data is generated based on the content of it and randomly hidden into the color attributions of other webpage-blocks based on the secret key. The validity of a webpage-block is determined by comparing the number of the inconsistent bits with the given threshold. If a webpage-block is judged as tampered, the displayed characters of the webpage-block are replaced with the given symbol to shield the tampered information, and the last-label attributions of it are changed to highlight the tampered webpage-block. These strategies not only prevent the spread of tampered information in webpage, but also make efficient use of the unmodified ones in it. Experimental results show that the file delta of watermarked webpage is smaller. The proposed method achieves a good imperceptibility and the tampered webpage-blocks are reasonably localized on the browser. And time efficiency is also improved.To improve performance of tamper detection and tamper localization accuracy, a webpage fragile watermarking algorithm based on leaf-element location is put forward. Firstly, a webpage is divided into webpage-blocks according to the leaf-elements which are the leaves of DOM tree which comes from webpage source code. The dividing method aims at locating text and images on the browser respectively. And then for each webpage-block, the watermark data is generated based on it’s content and randomly hidden into other webpage-blocks. Finally, webpage-block is determined by comparing the number of the inconsistent bits with the dynamic threshold which is selected adaptively. Theoretical analysis and experimental verification show that the proposed algorithm achieves high localization precision. What’s more, the proposed scheme can accurately detected and located the text and image on the browser even the tampered portions is up to20%of the watermarked webpage.Finally, a simulation system for the algorithms is completed, and the simulation results are analyzed.