Audio Steganography for Information Hiding and Covert Communication - A Tutorial

Steganography is concerned with hiding information in a medium such as text, image, audio or video. From Egyptian hieroglyphs, Greek tattooed writing, and Chinese papyrus to text display or printout from a word processor, this data hiding technique has a long and varied history. Human auditory and visual imperfections, which lead to psychoacoustic masking effects in hearing and vision, respectively, are exploited in modern multimedia hiding methods for modifying a host, or cover, signal in accordance with a given piece of covert information. Since the modification is carried out in the masked regions of perceptibility, the information-embedded medium, or the stego' signal, appears to be the same as the original host signal in human perception. While encryption of a media signal (an audio, image or video) alters the signal to conceal its contents so that it becomes unintelligible, embedding uses the media signal as a carrier for hiding covert information without altering the perceptual quality of the carrier. Hence, the success of embedding information in a media signal depends, among others, on the detectability of any difference between the original host signal and the embedded, stego signal. Watermarking is a subset of steganography for unobtrusively concealing a small amount of information such as the authenticity of the cover media signal. Recovery of the hidden information without requiring the original host media signal oblivious recovery and robustness of the hidden information under adverse conditions during transmission are also essential in many applications of steganography. Additionally, the hidden information must withstand intentional or unintentional attacks in attempts to illegally access the information from the stego. Applications of general steganographic techniques abound in modern Internet based communication and file sharing. Watermarking of an audio signal, for instance, is used to determine the legal use of a music file that carries a hidden copyright logo or other information. Embedding biometric data such as a person's fingerprint features in his/her picture identification card for use in access-controlled areas can thwart illegal entry. By concealing the existence of hidden information, the technique can be applied for covert communication using unclassified channels without undue demand for bandwidth.