Steganography
Steganography is the hiding of a message by a physical means. This has been used as a way to protect valuable information in many cultures throughout history, and there are many inventive methods that have been used. The first recorded use of Steganography is detailed by Herodotus in his Histories from around 440BC.
In this account, we are told of a warning sent to Greece of a forthcoming attack, that was written on wooden backing of a wax board, before the wax was poured in. Wax boards were commonly used in Ancient Greece for notes, as they were reusable (by melting the wax and scraping it flat, previous notes were removed). In essence they are the forerunner to pencils and rubbers! By using the board beneath the wax, the warning could be sent to Greece, without their enemies discovering it (unless they happened to melt and remove the wax, which they had no reason to do).
In this account, we are told of a warning sent to Greece of a forthcoming attack, that was written on wooden backing of a wax board, before the wax was poured in. Wax boards were commonly used in Ancient Greece for notes, as they were reusable (by melting the wax and scraping it flat, previous notes were removed). In essence they are the forerunner to pencils and rubbers! By using the board beneath the wax, the warning could be sent to Greece, without their enemies discovering it (unless they happened to melt and remove the wax, which they had no reason to do).
There are many other instances of Steganography being used throughout history such as:
These methods all have one major weakness, which is that they rely heavily on not being discovered, since if they are discovered, then the enemy can immediately read the information that was supposed to be secure.
In recent times, with the advent of computer, methods have become more sophisticated, and digital methods now exist to hide information. These range in complexity, and for most are unusable (as you need to have a very good understanding of how to use a computer to hide the message).
One such example is to hide an image "beneath" another image, by adding extra details. See the images below for an example.
- Writing messages on the body of a messenger - again from Herodotus, we are told of a wealthy man who tattooed a message on the scalp of one of his slaves, and allowing the hair to then grow over the message. The slave could then be sent to the recipient, who shaved off the hair to reveal the message.
- Using different font types to reveal a message in a piece of seemingly trivial text - in the paragraphs above the italic letters spell "codebreaking is fun".
- Using invisible inks, which are only revealed under a special light or by heat etc.
- Messages written in Morse Code on yarn that is then knitted to make a piece of clothing.
- Written on an envelope beneath the stamp.
- In 1966, Jeremiah Denton blinked in Morse Code during a forced televised press conference by the North Vietnamese. He spelled out the word T-O-R-T-U-R-E, and confirmed for the first time that American Prisoners of War were being tortured.
- During and after World War II, many spies used microdots, which are tiny discs with tiny lettering printed on them. These are then hidden on a piece of paper (under a full stop perhaps).
These methods all have one major weakness, which is that they rely heavily on not being discovered, since if they are discovered, then the enemy can immediately read the information that was supposed to be secure.
In recent times, with the advent of computer, methods have become more sophisticated, and digital methods now exist to hide information. These range in complexity, and for most are unusable (as you need to have a very good understanding of how to use a computer to hide the message).
One such example is to hide an image "beneath" another image, by adding extra details. See the images below for an example.
This image has another image hidden in it. To reveal the original image, remove all but the two least significant bits fro each colour component, and then normalise the image.
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This is the revealed image from the image to the left
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In the modern world, Steganography is still used in some instances. Many printers now use Steganography to identify which printer has been used to print a particular page (acting a little like a serial number). The printer will add tiny yello dots in a unique arrangement on the page, which can only be seen under a magnifying glass.
The weakness of Steganography is tackled by Cryptography. This method of secret writing involves making systematic changes to the message that is to be sent, which can only be undone by the intended reader of the message (who is the only other person who knows the method that was used to change the message). Of course, it is often the case that people wanting to send secret messages use both Steganography and Cryptography, which makes the message even safer from detection by prying eyes, since they would first have to find it, and then they would have to decrypt the scrambled message to retrieve the actual text.