Steghide is a steganography tool which is able to hide data in "container
files" and to extract this data again. If you do not know what steganography is
take a look at Neil F. Johnson's paper about steganography at
http://www.jjtc.com/Steganography/
Steghide is designed to be portable and configurable and features hiding data
in bmp, wav and au files, blowfish encryption, MD5 hashing of passphrases to
blowfish keys and pseudo-random distribution of hidden bits ("stego bits") in
the container data.