ABSTRACT
It is the science of transmitting a message between two parties (Alice and Bob) in such a manner that an eavesdropper (Eve) will not be aware that the message exists. The terms “information hiding” and “steganography” are often, but incorrectly, used interchangeably. Information hiding is the broad term for the scientific discipline that studies topics such as covert and subliminal communication channels, detection of hidden information (e.g., steganography), watermarking of digital objects, and anonymity services. Unlike cryptography, which seeks to hide the
content
of the message, with steganography we seek to hide the
existence
of the message. Steganographically hidden messages are inserted into legitimate and obvious (with respect to Eve) communications between Alice and Bob. Eve’s steganographic challenge, therefore, is to detect the message, not to understand it. Of course, steganography and cryptography can be used in conjunction, so that message content may be protected cryptographically, even if the steganographic “shield” fails and the existence of the message is discovered.
