History of Steganography

	Revision 4 . . November 7, 2001 5:58 am by Lee Daniel Crocker [Rewrite. Needed much more than copyediting.]
	Revision 3 . . (edit) November 1, 2001 1:08 am by Tbc
	Revision 2 . . November 1, 2001 1:01 am by Tbc [fixed typos, added /Talk (boy, that was fast work from request to reply!)]
	Revision 1 . . November 1, 2001 12:33 am by Aristotle [First draft. Feel free to correct or extend.]

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Difference (from prior major revision) (no other diffs)

Changed: 1c1,2

Steganography is the art or science of writing hidden messages.

Steganography is the science of writing hidden messages, where "hidden" means not only that the message cannot be read by anyone other than the intended recipient, but also that no one else even knows that a message has been sent. Generally a steganographic message will appear to be something else, like a shopping list, an article, a picture, or some other "cover" message.

Changed: 3c4,6

Generally a steganographic work will appear to be something else, like a shopping list, an article, picture or any form of electronic media. It differs from regular cryptography as often encoded works are sent to someone in a form that is obviously encoded with the strength of the encryption providing the protection.

Steganographic messages are typically first encrypted by some traditional means, and then a cover message is modified in some way to contain the encrypted message. For example, the letter size, spacing, typeface, or other characteristics of a cover message can be manipulated to carry the hidden message; only the recipient (who must know the technique used) can recover the message and then decrypt it. Francis Bacon is known to have used such a technique to hide messages in hand-written letters.

Changed: 5c8,9

A very old type of steganography is the secret method of communication used by the Roman empire. They would send strips of paper that would make no sense unless they were bound around a rod of a specific diameter that was carried by Roman commanders. These messages were created by the steganographer writing on the paper strips wound around such standard rods.

The larger the cover message is (in terms of data content) relative to the hidden message, the easier it is to hide the latter. For this reason, digital pictures (which contain a large amount of data) are commonly used to hide messages on the Internet and on other communication media.

Changed: 7c11

[Digital watermarking]? generally uses this type of approach so people either don't know that a watermark exists or cannot work out how to remove it.

Steganography can be used for [digital watermarking]?, where a message (being simply an identifier) is hidden in an image so that its source can be tracked or verified.