The Research On Information Hiding In MPEG-2/4Advanced Audio Coding(AAC)

With the internet applications and multimedia technology developing rapidly,multimedia-carrier digital communication between people has become an importantmean to exchange information. While multimedia technology brings convenience, thesecurity of multimedia information has become increasingly prominent in the digitalworld and is a very urgent issue to be addressed. Information hiding is proposed anddeveloped to solve this problem. According to the different audio carrier format,audio information hiding can be divided into information hiding for uncompresseddomain and those for compressed domain. The latter is more significant becauseaudio is always transmitted and saved in compressed format in real life. In this paper,we study the information hiding technology for AAC audio. The work mainlyincludes the following aspects.Firstly, The AAC encoding theory, which focuses on analysis of AAC audiocoding process, including every module in the process, is analysed.Secondly, The similarities and differences in the encoding process between AACand MP3are described. Analysis of both in the filterbank and quantization modulesare focused on to fully understand not only the differences but also the similar pointsbetween MP3and AAC, especially the reason why AAC has better sound quality inthe same ratio with MP3.Thirdly, Current information hiding algorithm is summarized. Meanwhile, four keyevaluation algorithms are introduced, which are hidden capacity, imperceptibility,robustness and security, as well as the relationship between them.Fourthly, A kind of hiding algorithm based on quantization and coding of AAC isproposed. The algorithm hides secret information based on the characteristics ofHuffman coding section. It’s simple because the whole hiding process is completedwithin the process of Huffman coding. The experimental results show that theproposed algorithm has good performance for hiding capacity and secutity, especiallyfor imperceptibility.Fifthly,Two kinds of hiding algorithm based on AAC bitstream are proposed. Thefirst one hides secret information using the characteristics of the sign bits of Huffman codeword, while the second one by swapping two Huffman codes with the principle of Huffmancodeword mapping. The whole process of the two algorithms are completed in thebitstream, so they are both simple, real time and practical, in addition, have high capacity,good imperceptibility, and certain undetectability.