Steganography

Introduction

Steganography is a very interesting form of secret communication. One of the drawbacks (if it is considered a drawback) of cryptography is the mere fact of knowing that communication is going on secretly. On the other hand, with steganography that fact could itself be hidden. However, cryptography is the stronger of the two. Steganography is the art form of hiding an intended message within another publicly viewable “cover” message. The word steganography derives from the Greek words steganos and graphein meaning covered and to write respectively.

Bit of History

Hiding a message can be done in numerous ways. Before computers a “cover” message could be used that would contain the embedded message within it. For instance, every 12th letter of the cover message could be used as the hidden message. In Ancient times, one ludicrous method was to tattoo a person’s bald head with a message and with some time hair of course, would grow concealing the message. Once at the destination the head could be shaved and the message revealed. Other methods consisted of letter heights, using various chemicals for invisible ink and even microdot pricks, which became popular during World War II.

Today

Currently, the most sophisticated forms of steganography are embedding messages within digital pictures such as a Graphics Interchange Format file, a sound file and even video files. The trick is to alter the file’s non-significant bits (for containing the message) such that the file itself does not show any visual or audio sign of alteration. The sender and receiver just need to be coordinated, perhaps by having the embedding and extracting private algorithms to know how to send and receive a secret message. As codebreakers uncover disguise after disguise, it becomes an ongoing race to find unique ways to conceal messages. Combined with encryption, however, this form of secret communication would then be very strong because once the message is located it then becomes a case of trying to decrypt it, which would be the case in normal cryptanalysis.

Steganography is important for practical reasons as well, for instance in copyright and watermarking. If you have developed a digital picture for instance and don’t want anyone else to use it unless they pay you the royalties then you can embed a particular set of bits into the picture (enough not to change it visibly of course) such that you could track and identify your digital property anywhere it’s being used. Watermarks can be set up in a fashion that doesn’t allow effective alterations to the media as well such as when someone wants to alter your picture it will cause an undesirable affect perhaps by placing a big off color X on top of the picture.

Links

http://www.jjtc.com/Steganography/
http://www.jjtc.com/pub/r2026.pdf
http://www.msg.net/utility/whirlgif/gif87.html
http://256.com/gray/docs/gifspecs/
http://astronomy.swin.edu.au/~pbourke/dataformats/gif/