History of Steganography

Recounted by Greek historian Herodotus:
Histiaeus, a Greek tyrant, was being held prisoner by a rival king. He wanted to send a message to his son-in-law without it being noticed. He decided to shave the head of a slave, and tattoo the message on the slave's head. The slave then waited for his hair to grow back before making the journey to deliver the message to Histiaeus' son-in-law.

Herodotus also provided the following story:
A nobleman from Medea wanted to send a message to a potential ally. He hid the message in the belly of an unskinned hare. The hare was delivered by a messenger, who was disquised as a hunter.

This is the third story from Herodotus:
A soldier named Demeratus had to send a message to Sparta that an attack was coming. The Xerxes planned to invade Greece. Demeratus took a wax-covered tablet, then the writing medium, and removed the wax. He then wrote his message on the wood of the tablet, and re-covered the tablet with wax. This allowed the tablet to appear as though it were blank, and the message to be sent undetected.

Ancient Romans would use substances such as fruit juices, urine and milk to create invisible inks. They would then use these inks to write messages between the lines of a visible message. The hidden messages would be revealed when the invisible inks were darkened from being heated. This method began being used in the first century AD, and lasted through World War II, with vinegar also being used to make the invisible ink.

Amorosa visione by Giovanni Boccaccio contained a signature to identify it as his work. Three sonnets were encoded into the first letters of the first verse of each tercet from other poems.

This technique was originally conceived in China, then reinvented by Cardan in the 1500s. The letters of the secret message form a random pattern that can be accessed simply by placing a mask over the text. An example provided by Fridrich is taking the secret message then changing the letters to the next one in the alphabet. The new letters are then placed in a fake message, with the first letter of certain words being the encrypted secret message. The words that contain the message are chosen using a numerical sequence, in this case pi. For example, the first letter of the third word of the cover message is the first letter of the encrypted secret message. The first letter of the next word of the cover message is the second letter of the encrypted secret message. The first letter of the fourth word after that is the third letter of the encrypted secret message, and so on.

Johannes Trithemius, a monk who is considered to be one of the founders of modern cryptography, hid secret messages in his three volume work Steganographia. He used long prayers consisting of the names of angels to hide secret messages. The messages would appear as a pattern of letters. For example the prayer could be: "padiel aporsy mesarpon omeuas peludyn malpreaxo." To discover the message, use every other letter in every other word. The hidden message is: "prymus apex".

The "Ave Maria" cipher was also invented by Johannes Trithemius and appears in Stegranographia. The work contains a series of tables. In each table is a list of words, with each word corresponding to a particular letter. The message is coded by replacing each letter of the message with the corresponding words from the tables. The message will appear to be a prayer if the tables are used in order, and one table is used per letter.

During the Boer War, the British enlisted Lord Robert Baden-Powell to be a scout. He was to find the positions of Boer artillery bases, and mark them on maps. In order to avoid suspicion, if he was caught by the Boers, he would make drawings of butterflies out of the markings. Certain markings on the wings of the butterflies represented the positions of the Boer military installations. However, when looking at the butterflies, one could not tell this information was hidden among the drawings.

German spies during World War I would report British warships by using fake cigar orders. The orders would represent the different types of warships. For example, the order "500 cigars needed in Portsmouth" meant "five cruisers were in Portsmouth".

During World War II, a German spy sent this message: "Apparently neutral's protest is thoroughly discounted and ignored. Isman hard hit. Blockade issue affects pretext for embargo on by-products, ejecting suets and vegetable oils." The hidden message is: "Pershing sails from NY June 1," which can be found using the second letter of each word.

Developed by the Nazis during World War I, the microdot was a photograph the size of a typed period. When the photograph was developed, it could reproduce to a standard-sized typewritten page with excellent clarity. The Germans would use the microdots to transmit high volumes of printed data and technical drawings. The microdots were discovered by the Americans only after informed by a double agent. The agent warned: "watch out for the dots - lots and lots of little dots." The concept came from Brewster, who in 1857, developed the idea to shrink a message to the point where it resembles a speck of dirt, but still readable using high magnification.

Nazi spy George Dash used a special solution of copper sulfate to write messages on his handkerchief. The messages would only appear when exposed to ammonia fumes.

Navajo Indians, employed by the U.S. Marines stationed in the Pacific during World War II, would transmit messages, using a slang version of their native language, over the radio. Only 28 non-Navajos could speak and understand the Navajo language, and only those who knew the slang could understand the messages.

Commander Jeremiah Denton, a prisoner of war, was forced by his Vietnamese captors to give a television interview in 1966. He used the opportunity to send a message by blinking his eyes in Morse code to spell out "torture".

Digital fingerprinting is done by creating a metafile that describes the contents of the source file. An example of this would be encrypted satellite television broadcasting. Users "could be issued a set of keys to decrypt the video streams and the television station could insert fingerprint bits into each packet of the traffic to detect unauthorized uses. If a group of users give their subset of keys to unauthorized people, at least one of the key donors can be traced when the unauthorized decoder is captured." (Thampi)

This is hiding trademarks in images and music. The watermark contains information that will uniquely identify it, even from another image or piece of audio that looks identical to the human eye. The watermark is not detectable by looking at the image or listening to the audio file.