Watson Review - Summer 2011 - (Page 12)
Researchers uncover hidden messages
BY JIM H. SMITH
n the tense days after Sept. 11, 2001, The New York Times reporter Gina Kolata introduced readers to a new and decidedly scary way to communicate. “The investigation of the terrorist attacks … is drawing new attention to a stealthy method of sending messages through the Internet,” Kolata wrote. “The method, called steganography, can hide messages in digital photographs or in music files but leave no outward trace that the files were altered.” When Kolata’s article was published, Watson School Professor Jessica Fridrich, PhD ’95, had just created for the United States Air Force a powerful tool that made it possible to search, with a high probability of success, for one of the most commonly used technologies used to conceal information. Fridrich, a professor in the Department of Electrical and Computer Engineering, developed complex algorithms that could analyze the numbers used to encode pixels — short for picture elements — the miniature dots of which visual images are composed. Pixels are the smallest individual units of a picture that can be controlled in the reproduction process. They are so tiny that a single photo may contain thousands, or even millions, of them. So looking for messages hidden within a photo is daunting. But Fridrich’s novel algorithms were up to the task. Designed to scan the numerical sequences of the pixels, they looked for anomalies. Those variations, which produce slightly altered images — too small for the naked eye to detect — reveal whether an image is clean or contains secret messages.
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