2. Steganography

The word steganography literally means covered writing as derived from Greek. It includes a vast array of methods of secret communications that conceal the very existence of the message. Among these methods are invisible inks, microdots, character arrangement (other than the cryptographic methods of permutation and substitution), digital signatures, covert channels and spread-spectrum communications.

"Steganography is the art and science of communicating in a way which hides the existence of the communication. In contrast to cryptography, where the enemy is allowed to detect, intercept and modify messages without being able to violate certain security premises guaranteed by a cryptosystem, the goal of steganography is to hide messages inside other harmless messages in a way that does not allow any enemy to even detect that there is a second secret message present" [Markus Kuhn 1995-07-03].

David Kahn places steganography and cryptography in a table to differentiate against the types and counter methods used. Here security is defined as methods of "protecting" information where intelligence is defined as methods of "retrieving" information [Kahn67]:

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