Steganography via E-Books with the EPUB Format by Rearrangements of the Contents of the CSS Files

With the advance of information technology and mobile devices, e-book reading has become a popular way for people to gain knowledge. However, with the widespread uses of digital texts, issues about the copyright protection of e-books have arisen. The electronic publication (EPUB) format is currently one of the most widely used e-book formats. A novel data hiding method for steganographic applications is proposed in this study to hide secret messages into the e-book with the EPUB format. Specifically, the message bits are embedded into the cascading style sheets (CSS) file of the e-book using the lexicographical orders of the selectors and their declarations in the CSS rules. By making use of the fact that the selectors in a CSS file need not all be referred to, fake rules are created artificially, when necessary, to increase the data embedding capacity of the CSS file. The appearance of the e-book does not change after message embedding. Good experimental results and comparisons with other related methods show the feasibility and superiority of the proposed method.