Information Hiding in EPUB Files by Rearranging the Contents of CSS Files

With the recent rapid development of information technology and mobile devices, e-books have come to have a significant influence on people's reading habits. However, with the widespread use of digital texts, issues surrounding copyright protection have arisen. EPUB is currently the most widely used e-book format. This paper proposes an information hiding technology to hide messages in EPUB files. These hidden messages can be used to protect the copyright of e-books or to transmit secret information. The method embeds secret messages into EPUB files using the lexicographical order for coding information and rearranging the selector rules and their property declarations in CSS files. It also makes use of the fact that selector rules in a CSS file need not be referred by its associate XHTM files in order to insert fake selector rules into the CSS file to increase hiding capacity. The proposed hiding method does not change the outward appearance of EPUB documents in any way, so it is imperceptible. According to experiments conducted, the hiding method is feasible and effective.