The art of hiding signals inside other signals is called steganography ('covered writing' in Greek). By using unnecessary bits of information added to a file that contains sensitive data, the message is undecipherable to anyone but the recipient. It is an ancient craft that has seen a new lease of life with the onset of computer and online technology.
Steganography is currently in the news after it was reported that Osama bin Laden and his associates allegedly use it to send messages to one another.
This USA Today report went on to say that terrorists also hide maps and photographs in sports chat rooms, pornographic bulletin boards and other sites.
Steganography takes advantage of the fact that images, sound files and disks have portions of unused data, and replaces them with information. The file can then be exchanged without anyone being aware of what it contains. Steganography can also be used to place a hidden 'trademark' in images, music and software: a technique referred to as watermarking to avoid copying and illegal distribution.
A digital signature can also be embedded in a file, enabling authors to control and verify ownership of any digital information available online. This book has a lot of information on hiding techniques and digital watermarking. Another interesting article discusses steganography and how it is different from cryptography.
Different kinds of steganography software are now available, including Steghide, which embeds a message in .bmp, .wav and .au files, MP3Stego for MP3 files and Steganos that hides data in graphic and sound files. You can get a complete list here.
Bubbles is fascinated by the study of steganography. All he wants to do, he claims, is send a hidden proposal to his girlfriend, because he is too scared to ask her face to face!
ADDITIONAL LINKS:
Information hiding home page|
More about Steganography|
Steganography Resources|
Future of the Internet|
Secure Root Resources on Steganography
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