Research On Text Fragile Watermarking Technology

With the fast development of e-official and e-commercial, many important documents are passed through network. If those documents are tampered, the loss will be great. It's urgent to authenticate documents. Comparing with the digital signature, fragile watermark has the benefit of locating the tamper region and passing less information. So, text fragile watermark is studied to solve the problem of documents authentication.Main work has two parts as follows:(1)In the research of fragile watermark based on text image, the IMW algorithm is proposed. Firstly, image is cut into blocks according to the content of image. Chaotic mapping is used to ensure the security of watermark. Secondly, the wet paper code is used to embed watermark. The filppable pixels are fully used, as a result, embedding capacity is improved. Finally, the experiment result shows the algorithm can detect the location of tamper image and embedding capacity is as much as two times of the Min Wu's algorithm.(2)To slove the security problem of text fragile watermark based on WORD, a fragile document watermarking algorithm based on PDF is proposed. Firstly, PDF is converted to PS and then embed watermark in PS. Secondly, with the characteristic that trivial change of word's color won't introduce obvious artifact, watermark is embedded by changing the word's color. Thirdly, the document is cut into blocks according to the line, hashed value of the document block is taken as watermark. watermark is embeded into document block to authenticate the content and locate the tampered region. Finally, the experiment result shows that the algorithm can detect the location of tamper image and security is better than the algorithm based on WORD.