UniSpaCh: A text-based data hiding method using Unicode space characters

This paper proposes a text-based data hiding method to insert external information into Microsoft Word document. First, the drawback of low embedding efficiency in the existing text-based data hiding methods is addressed, and a simple attack, DASH, is proposed to reveal the information inserted by the existing text-based data hiding methods. Then, a new data hiding method, UniSpaCh, is proposed to counter DASH. The characteristics of Unicode space characters with respect to embedding efficiency and DASH are analyzed, and the selected Unicode space characters are inserted into inter-sentence, inter-word, end-of-line and inter-paragraph spacings to encode external information while improving embedding efficiency and imperceptivity of the embedded information. UniSpaCh is also reversible where the embedded infor-