Introduction and Goals

Social/Ethical Issues


Project Details

Evaluation and Conclusion


Background to Steganography

The earliest records of the use of steganography being used were recorded by the Greek historian Herodotus. When the Greek tyrant Histiaeus was held prisoner by King Darius in Susa during the 5th century BCE, he had to send a secret message to his son-in law Aristagoras in Miletue. Histiaeus shaved the head of a slave and tattooed a message on his scalp. When the slave's hair had grown long he was dispatched to Miletus. As soon as this steganography technique was discovered people were stopped at the borders, heads shaved and the message was revealed. Thus the technique became useless and unreliable and a new way to send messages had to be found.

In Ancient Rome, they used invisible ink to write between already written texts. The invisible inks used were substances such as fruit juices, urine and milk. These substances would darken and become legible when heated, allowing the message to be read.

Invisible inks were used frequently during World War II. They also used a form of steganography involving "null ciphers", which were unencrypted messages used to hide real messages. For example the following message was sent by a German spy during WWII

"Apparently neutrals protest is thoroughly discounted and ignored. Isman hard hit. Blockade issue affects pretext for embargo on by-product, ejecting suets and vegetable oils."

This message at face value look innocent and would not alert suspicion but if you were to take the second letter of ever word the secret message would be encrypted. " Pershing sails from NY June 1"

Another well-publicized example of steganography occurred during the height of the Vietnam War, when Commander Jeremiah Denton, a naval aviator who had been shot down and captured by North Vietnamese forces, was paraded in front of the news media as part of well-staged propaganda event. Denton knew he would be unable to say anything critical of his captors outright, so as he spoke to the media, he blinked his eyes in Morse code, spelling out T-O-R-T-U-R-E.

With the advent of photography, microfilm was created as a way to store a large amount of information in a very small space. In both world wars, the Germans used "microdots" to hide information, a technique which J. Edgar Hoover called "the enemy's masterpiece of espionage." A secret message was photographed, reduced to the size of a printed period, then pasted into an innocuous cover message, magazine, or newspaper. The Americans caught on only when tipped by a double agent: "Watch out for the dots -- lots and lots of little dots."

Modern updates to these ideas use computers to make the hidden message even less noticeable. For example, laser printers can adjust spacing of lines and characters by less than 1/300th of an inch. To hide a zero, leave a standard space, and to hide a one leave 1/300th of an inch more than usual. Varying the spacing over an entire document can hide a short binary message that is undetectable by the human eye. Even better, this sort of trick stands up well to repeated photocopying.

Steganography, as the above examples demonstrate, is not limited to one particular medium or technology -- it's simply a matter of disguising a covert message within an overt one, whether that overt message is an ancient wax tablet, a telegram or a person speaking through a television broadcast. So it should come as no surprise that the technique has also found its way onto the Internet. In fact, steganography tools are freely available for public use. Steganography software allows users to secretly incorporate data into various digital media - text, jpg images, MP3 audio files, etc.

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