Colour Image Steganography Using LZW Compression and Fisher-Yates Shuffle Algorithm

Steganography is the art and science that involves communicating secret data in an appropriate multimedia carrier, e.g., image, audio and video files, to conceal the very existence of the embedded data. This report presents a novel technique for colour image Steganography based on LZW compression and Fisher – Yates shuffle algorithm. Two 24-bit colour images are used as cover image and secret image respectively. Fisher-Yates shuffle algorithm is implemented to shuffle the pixels of secret image and LZW encoding is performed over the shuffled secret image/message before embedding and each LZW encoded bit of secret image/message is embedded inside the cover image by altering the last two least significant bit (LSB) of each of the pixel's intensities of cover image. LZW algorithm is organized around a translation table, referred to as dictionary that maps input characters into fixed-length codes. The LZW dictionary has a prefix property in that for every string in dictionary, its prefix string is also in the dictionary. A two-level compression performs compression of bit strings into 2-bit string. Two-level decompression performs decompression of 2-bit string into full length bit strings. Furthermore, satisfactory security is maintained since the secret image cannot be extracted without LZW dictionary, Fisher – Yates shuffle algorithm and two-level compression/decompression modules.