The history of steganography

There is a wealth of methods for creating encrypted messages you can't even tell are there

Current digital steganography – embedding encrypted messages within digital images – is said to be used by terrorists to pass along information, but much lower tech methods have been used for centuries for various forms of secret communication. Here is a brief history of how the art and science has evolved.

The word steganography came from a 15th century work called Steganographia by a German abbot named Trithemius. On the face of it, the three books were about magic, but they also contained an encrypted treatise on cryptography – so Steganographia was itself a case of steganography.


An ancient Greek named Histaiaeus was fomenting revolt against the king of Persia and needed to pass along a message secretly. He shaved the head of a slave, tattooed the message on his scalp, then sent him on his way when his hair grew back in. Recipients of the message shaved his head again to read the alert. The Greeks used the same trick shaving and writing on the belly of a rabbit.


Sometime in the 5th century B.C., an exiled Greek named Demaratus wrote a warning that the Persians planned to attack Sparta. He wrote the message on the wooden backing for a wax tablet, then hid it by filling in the wood frame with wax so it looked like a tablet containing no writing at all. The wife of the Spartan king divined that there was a message behind the wax, so they scraped it off and got the warning in time to set up a desperate defense at Thermopylae, incidentally giving modern screenwriters the plot for the movie "The 300".


Encoded messages have been knitted into sweaters and other garments. In this example, the blue dotted lines are Morse Code for, "My girlfriennd knit this." Yes, the sweater has a typo – an extra n in girlfriend - according to the woman who knitted it.


During World War II, microdots - miniaturized photos that can be hidden in plain sight, then read using magnifiers – were used by spies to carry data out of enemy countries. Here the microdot circled in red piggybacks on a watch face. Blown up, it reveals a message written in German.

Velvalee Dickinson

Also during World War II, an American named Velvalee Dickinson sent steganographic letters about U.S. military ships to Argentina for delivery to Japanese intelligence. The letters seemed to be about her doll business, but they actually were about U.S. military strength. Decoded, the letter shown here reads: "I just secured information on an aircraft carrier, it had been damaged, that is torpedoed in the middle. But it is now repaired ... [t]hey could not get a mate for this so a plain ordinary warship is being converted into a second aircraft carrier ..."

USS Pueblo

When the USS Pueblo was captured by North Korea in 1968, the crew was forced to pose for propaganda photos to demonstrate they were being well treated. Their finger gestures are a form of steganography that sends a message Americans could decrypt right away, the North Koreans, not so quickly.

Digital photo steganography uses code fields for unimportant bits as places to hide encoded messages or images. While such manipulation might slightly alter the quality of the original image, it generally goes unnoticed by the naked eye. In these pictures, the image of the cat has been embedded in the image of the branches against the sky.

Copyright © 2009 IDG Communications, Inc.

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