| Steganography (from Greek steganos meaning covered) differs from classic cryptography (from Greek kryptos meaning hidden) in that it is the very existence of the message is disguised rather than being a jumble of letters and numbers where there is clearly a message - but not one that is intelligible to anyone without the key.
Steganography can be divided into two branches:
- Technical steganography
- Linguistic steganography
Technical steganography
This branch includes invisible inks - some of which have been in use since Pliny's time. One of these ancient recepies is that of onion juice and milk which turns brown under heat or UV light. Boxes with false bottoms also fall into this category.
One of the earliest documents that describes steganography is from the Histories of Herodotus. In this story, Demeratus wanted to notify Sparta that Xerxes of Persia intended to invade Greece. To send this message, he scraped all the wax off of a writing tablet, write the message on the wood and then recovered the tablet with wax. As these tablets appeared to be normal messages they passed inspection. The Battle of Thermopylae followed, and although the message was discovered by Gogo, wife of King Leonidas, Sparta lost the battle - outnumbered 100,000 to 1,000 and fighting on two fronts.
Another ancient account of Steganography tells of when the Greek tyrant Histiaeus was held prisoner by King Darius. There, he sent a message to his son-in-law Aristagoras by shaving the head of a slave and tattooing a message on the scalp. Once the slave's hair was long enough, he was sent to deliver the message.
The modern methods of steganography include high speed telegrams (a spurt of 20 characters per second of Morse code) and frequency subband permutation ("scrambling"). A revolution in written steganography occurred with microphotography. With a microphotographic dot the size of a spec of dirt - a significant improvement from the 'macrodot' of a slave's head. Microdots where invented in the 1920s by Emanuel Goldberg. Rudolf Abel (a Russian spy) was able to produce his microdots from spectroscopic film - a material he could buy without attracting undue attention. In World War II, the microdots used by the Germans were the same size as a period in a typewritten document.
Linguistic steganography
Linguistic steganography can be broken down into to methods: either it is an 'innocent' message in open code, or it is expressed in visible differences in the script or drawing in a semagram.
The latter form is rather popular with amateurs in cryptography and has been around for some time. Francis Bacon invented two type faces for sending secret messages. At about the same time, this idea is mentioned in Paris by Vigenère. The most recent known use was in A. van Wijngaarden's alleged use of roman and italic periods in the ALGOL 68
report.
Yet it is important for us to see the use of what can be alik and different.
(The message "You suck" is hidden in the above text)
Variants on this idea include marking specific characters with punctuation or lowering certain characters. In 1976, the lowering method was used in a German textbook on combinatory logic with ever so slightly lowered characters preaching "Down with Soviet imperialism".
Another method uses the spacing between letters within a word. In cursive, it is quite easy to 'break' the flow. Then counting the number of characters in each stream provides a numeric code. This has been known in Russian anarchist circles, and was combined with the "Nihilist cipher". This method was also used by German U-boat officers in POW camps to report home on the Allied anti-submarine tactics.
Semagrams can also be encoded in pictures. The most well known form of this is in the secret message in The Adventure of the Dancing Men by Sir Arthur Conan Doyle. Long and short stems of grass in a picture may be disguised Morse code. Mazes can also encode messages in may ways. Autosterograms (Magic eye) drawings can also hide messages - for a little while at least. | 
