Information Hiding And Detecting Based On PDF Document

The study of information hiding focuses on how to embed processed significant secret information to the other one named cover, and how to extract possible secret information from the cover. The embedding and extracting are two symmetrical processes, and the main issue is how to embed the information, i.e. hiding algorithm. Hiding algorithm depends on the type of the cover. As text files are widely and frequently used, information hiding based on text files is of great significance. In the field of text information hiding, most algorithms are based on formats of plain text, imaged text, Word, web files, etc. But information hiding algorithms based on PDF file are few, and the works are not perfect. In this paper, information hiding and detecting algorithms based on PDF file are studied. The main research work in this paper is as follows:Firstly, after analyzing the data structure of the PDF file, a novel information hiding method based on the structure of PDF file is proposed. Above all, the secret data is camouflaged to form the legal PDF object, and then the data will be embedded in the cover PDF file by operating the document stream. The embedding won't affect the output of the readers, the editors and the printers. Theoretical analysis and experimental results show that the algorithm can achieve large capability, high speed of hiding and detecting, and security which depends on the encrypted algorithm and the key. It is obviously better than WbStego software in terms of capability, security, and transparence.Then, after analyzing the formatting statement data of the PDF document, a novel information hiding algorithm based on PDF document's redundant data is proposed. Firstly, the data blocks of each text run formatting statement that are redundant and stable are confirmed, then the encrypted information is embedded by modifying those blocks to hide information. The experimentation shows that, the algorithm has large capacity of information hiding; it's more transparent and more robust under the general manipulations of Adobe Acrobat Professional such as additions of notation, postil, stamp, signature, background and linearization of the PDF document.Lastly, an all-purpose system of PDF file secret information detection is implemented. Several present information hiding algorithms based on PDF file's storage structure are summarized, then an all-purpose detection algorithm is proposed. The system is capable of detecting similar secret information in all parts of PDF file simultaneously, and has made a good showing in detection speed, false alarm rate and missing alarm rate. The above system has also been generalized and implemented for real applications.