A Multiple Watermarking Scheme for Content Authentication of OOXML Format Documents

The content of the document tends to be tampered and forged easily, and it may cause serious consequences in many important situations. Therefore, this paper proposes a multiple watermarking scheme for copyright protection and tamper detection of OOXML format documents. For an OOXML format document, we firstly embed a robust watermark by synonym substitutions, then embed double watermarks fragilely by utilizing the format characteristics of the document. The double fragile watermarks are embedded by the ways of modifying the word number in a text element defined by the main document body and modifying the values of revision identifiers. The embedding of multiple watermarks does not cause any visual impact on the content and format of the original document, which maintains the original meaning of the content basically. As shown by the experimental results, the watermarking method based on synonym substitutions has a strong robustness against the attacks on formats and the content. However, the double fragile watermarking methods can sensitively perceive tampers in the content and formats of the watermarked document, and predict the type of tampers with capability of locating the tampering.