steganography - Computer Definition
From Greek and translating as covered writing or hidden writing, and dating to 440 B.C., steganography is the art or science, or system, of hiding the existence of a message. In The Histories of Herodotus, the Greek historian Herodotus mentions several examples. Into the wood backing of a wax tablet, Demeratus carved a message warning his countrymen of an impending attack. He then applied the wax, which hid the message from view until it was removed by the intended recipient. Another method involved shaving the head of a slave and tattooing a message on his scalp. After the hair grew back enough to cover the message, the slave could be sent through enemy lines, and his head could be shaved again to read the message. More recently, microfilm dots have been hidden under postage stamps, or disguised as punctuation marks in typewritten letters. Contemporary stenography takes more technologically sophisticated forms, such as a message hidden in a data file, for example, in an HTML file, a JPEG file, or an MP3 file. Such a hidden file also is typically encrypted for additional security. See also encryption and watermark.
The practice of hiding information in e-pictures, MP3 music files, or any binary data format that can be changed without invalidating the data format as well as retain the appearance of being unaltered. Steganography is successful because it is based on the fact that digital images and MP3 music files are comprised of thousands of pieces of binary code instructing a computer to color a pixel or to produce a certain sound. Because of the large number of digital information pieces involved, a few can easily be changed to convey secret messages without having a significant impact on the overall effect produced for the normal eye or ear. The secret information tends to be stored in the least important parts of a digital image or MP3 tune.
Consider the potential that steganography could have for terrorists trying to communicate with each other over the Internet. In a holiday e-picture, for example, dozens of pixels in the background could be altered to convey an airline’s schedule, and to some casual observer or to an FBI agent, the picture would likely appear to be “innocent” because the majority of the pixels would be left unchanged. However, anybody who was told where to look could access the information hidden in the amended pixels, which could then be put together and read.
Steganography involves a simple procedure that can be performed with software purchased from stores or downloaded from the Internet. The main reason for using steganography rather than cryptography is that anything encrypted tends to draw attention to the fact that some important information is deliberately being hidden.
Carter, S. Clinic: What is Steganography? [Online, 2004.] ITSecurity.com Website. http://www.itsecurity.com/asktecs/oct2301.htm.
Hiding a message within an image, audio or video file. Used as an alternate to encryption, it takes advantage of unused bits within the file structure or bits that are mostly undetectable if altered. A steganographic message rides secretly to its destination, unlike encrypted messages, which although undecipherable without the decryption key, can be identified as encrypted. For a white paper on the subject written by Neil F. Johnson of George Mason University, visit www.jjtc.com/Steganography. See ScramDisk and social steganography.