DEVELOPMENT OF AN AUDIO STEGANOGRAPHY SYSTEM USING DISCRETE COSINE TRANSFORM AND SPREAD SPECTRUM TECHNIQUES

Abstract

In today’s electronic society, security of information is an issue of major concern especially in the communication domain. Indeed, there is a very serious need for schemes that guarantees security of information exchange between entities, over public networks. Several techniques that includes but are not limited to cryptography and /or steganography have been proposed in both research communities and the academia. In cryptography, the structure of a message is scrambled to make it meaningless and unintelligible unless the decryption key is available. However, as the need for security increases, cryptography alone becomes insufficient, so steganography could serve as a supplement to encryption. Although steganography is not a direct replacement for cryptography, but steganography along with cryptography gives more security to data. Audio steganography hides data in selected audio files. Several audio steganography works exist, but their major limitations include their inability to embed information in multiple audio file formats, high distortion rate and low level of robustness of their resultant stego files. This research attempts to proffer solution to the obvious challenges of the previous works of Wheeler et al., (2012), Olanrewaju et.al., (2013) and Yekta et al., (2014) by developing an efficient and robust audio steganography system for the security of information whether in store or on transit across the Internet. This is achieved by first encrypting a given secret information using the Advanced Encryption Standard (AES) algorithm. The resultant ciphertext is then compressed using the Huffman and Lempel Ziv Welch (LZW) algorithms respectively. Then, a suitable cover medium, which is an audio file is selected and decomposed into frames using one dimensional Discrete Cosine Transform (DCT). The frames thus created are queued based on the frequency of their energies. The low frequency components of the frames are selected because they are below the perceptual threshold of the human auditory system (below 20 Hz), so that the secret message does not introduce any audible distortion into the original audio signal or file. Bits of the ciphered secret message are then embedded into the selected low frequency component frames, using the frequency hopping spread spectrum technique, to produce an audio stego file which is not distinguishable from the original audio cover file. Results of performance evaluation of the developed system shows that it has very low level of distortion as revealed by the Signal to Noise Ratio (SNR). The compression ratio obtained is also equal to one (1), which shows that the cover audio file is identical to the resultant stego file.