Monday, 9 June 2008

What is Steganography?

Provos and Honeyman (2003) define steganography (aka stego) as “the art and science of hiding communication; a steganographic system thus embeds hidden content in unremarkable cover media so as not to arouse an eavesdropper’s suspicion”.

The majority of modern steganographic systems begin with discovering the redundant bits within the host media or data. The goal is to be able to modify the host data in a manner that does not obliterate the integrity of the source data. Another objective of steganography is to not be detected in the host file. It is in effect, a means of hiding data within other data.

Although modern steganography is a relatively modern field, both Richmond (1998) as well as Johnson & Jajodia (1998) mention an ancient example. In their paper they note the example of an early steganographic system. Richmond notes the practices of the ancient Athenians where the head of a messenger was shaved and subsequently tattooed with a message that would be covered with hair rendering it unseen if the messenger was captured. Johnson & Jajodia mention how this same system was adopted by a Roman general who shaved a slave’s head and tattooed a message on it sending the messenger on the errant after the hair grew back.

The majority of steganographic methods that have been developed in modern times have been centered on hiding a message within images and audio files (such as BMP., GIF, JPEG, WAV and MP3 file formats). A number of other methods include hiding messages within Word documents or even within embedded macros and Metadata.

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