The Research On Information Hiding For Powerpoint Files

Information hiding has become a new hot interest area in the research of information security in recent years. It is a technique that embeds secret information imperceptibly into a cover media, by employing some redundancy with random characteristics of the cover media. Through this, it is hard for attackers to obtain the location of secret information because of the"hiding"of the existence of this information, and then the security of secret information is enhanced. Among various types of cover media, text is kind of one that is used most widely, hence it is with great value to study text information hiding. In text information hiding field, however, most current researches focus on plain text, image text, Word, PDF and web files. PowerPoint files (PPT) are widely used today but steganographic schemes for them have rarely been reported. In this paper, information hiding algorithms based on PPT files are studied, and the main research work is as follows.By analyzing the PPT file format, a file parser is designed and implemented. The tool can directly extract text attributes, pictures, remarks, slides information, and text contents from PPT files. It does not rely on any other software, and can run with high speed & steady state.A steganographic method based on file-update is proposed with large hiding capacity. The PowerPoint application of 97~2003 editions employ a file incremental update mechanism to organize PPT files. This mechanism improves the efficiency of file maintenance, while it can also produce redundant data within a file. Our method just takes use of these redundant data to hide secret information. Experiment results show that the scheme performs well in terms of hiding capacity, imperceptivity, security, and speed of information insertion and extraction.A new steganographic method based on text format is proposed. Firstly, segment the text of a presentation to obtain several groups of words with different part-of-speech: nouns, adjectives, and verbs etc; then select some important words and adjust the color of these words in a significant way that hide secret information in the LSB bits of color. On the one hand, the statistic characteristics of color of the stego-text are similar with normal texts, so it is not easy to be detected by steganalysis tools; on the other hand, the method does not affect the appearance of a presentation too much, because they are common operations to adjust the colors of some important words to emphasize them.A steganographic method based on animation effect is proposed. Firstly, choose a group of animation effects and obtain the appearance frequency of each of them using statistical method; next perform Huffman coding on these effects with their frequencies to produce a Huffman tree, and each effect can match a Huffman code; then perform Huffman de-coding process on the secret message with the tree to obtain a series of effects (the original secret message can be assembled by the Huffman codes of these effects); finally apply these effects on a presentation to achieve information hiding.