http://spectrum.ieee.org/aug08/6593



By Sally Adee

First Published August 2008

IEEE Spectrum



Earlier this year, someone at the United States Department of Justice 

smuggled sensitive financial data out of the agency by embedding the 

data in several image files. Defeating this exfiltration method, called 

steganography, has proved particularly tricky, but one engineering 

student has come up with a way to make espionage work against itself..



Keith Bertolino, founder of digital forensics start-up E.R. Forensics, 

based in West Nyack, N.Y., developed a new way of disrupting 

steganography last year while finishing his electrical engineering 

degree at Northeastern University, in Boston..



Steganography uses innocuous documents, usually an image file, as 

carriers for secret messages. Unlike encryption, steganography encodes 

the message while at the same time concealing the fact that a message is 

being sent at all. The Greek-derived name means "covered writing." The 

earliest steganographers were said to be Greek generals who tattooed 

sensitive information onto the shaved heads of messengers. Once the hair 

grew back, the messenger could travel without suspicion to the intended 

recipient, who "decrypted" the secret message by shaving the messenger.s 

head again. In its current incarnation, steganography often makes use of 

e-mail, an ideal carrier for any corporate spy, disgruntled employee, or 

terrorist. ?



Steganography algorithms vary widely.digital forensics firm WetStone 

Technologies Inc., of Ithaca, N.Y., lists 612 applications - but they 

work on basically the same principle. To embed a message in an innocuous 

image of a cat, for example, a commonly used steganography algorithm 

called LSB takes advantage of the way computers digitally encode color. 

The algorithm hides the fugitive file inside the so-called noncritical 

bits of color pixels. Noncritical bits are just what they sound like.the 

least important information in a pixel. A gray pixel in the cat.s 

uniformly gray fur, for example, is coded as a number that looks 

something like 00 10 01 00. By changing the least significant bits.the 

last two.you introduce one-millionth of a color change, an absurdly 

subtle alteration that no human eye could detect. ?



[...]





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Received on Mon Aug 25 2008 - 02:14:03 PDT