Steganography: the art of hiding information in plain sight

Steganography is the art (as well as the science) of communicating in a hidden way. It is referred to as "transmission security", or TRANSEC in military literature. Its goal is to hide messages inside other "harmless" messages in such a way that an "enemy" would not even know a second secret message was present. The history of steganography is discussed as is the design principle of steganographic systems. Some examples are given.