Research And Application Of The PDF Document's Security Based On Digital Right Management System

The Portable Document Format (PDF) has been recognized as a general electronic document format for the advantages of fast-generating, high degree of simulation and compression ratio. The concern of the security problem of this kind of document has also been aroused gradually. Although the Acrobat's standard password encryption achieves the goals of protecting and legally authorizing the document, it can't be applied massively during the Intranet's transmissions for its inconvenient procedure and oversimplified way of certification. As a result, an efficient and flexible security solution needs to be studied and designed in this thesis. The main works are as follows:1. At first, the functions and methods of several common tools for PDF encryption are studied and analyzed. The theoretical and practical achievements of PDF encryption at home and abroad as well as their characteristics and shortcomings are described and analyzed. It is proved that there are some limitations in current document encryption.2. The syntax and structure of the PDF are studied in detail, of which the mechanism as well as the procedure of the password encryption is explored specially and the algorithms for generating passwords of encryption and authentication are described. Based on these, the password encryption's function is reproduced in external environment. This program, which is separated from the plug-in environment, makes batch-process possible and lays a good foundation for creating new mechanism of encryption.3. In view of the standard password encryption, the two-stage encryption is proposed creatively that separates the procedure into two phrases on the aspect of time and physics. Firstly the original file's streams are encrypted on the server of headquarter to be downloaded, and then the application server fills the authentication information into the stream-encrypted files according to the configuration generated by the authorization module. Based on this mechanism, a PDF digital right management solution is designed which mergers various technologies, such as input and output (IO) of file stream, plug-in, browser helper object (BHO) and file hook together. The manager of system could make free combination of arbitrary kinds of authorization, such as IP address, timestamp, host signature and user permissions, to achieve a flexible control on document security.The functions of the encryption and authorization modules are carried out by this dissertation. The interface is friendly, clear and easy to operate. The system which uses multithread technology to guarantee its real-time controllability has been put into practical use in the Electric Power Research Institute of Anhui Province successfully.