Digital detective hunts hidden messages

Charles Boncelet, professor of electrical and computer engineering

1:02 p.m., Jan. 28, 2005--A University of Delaware research team has received National Science Foundation funding to combat terrorism by developing techniques to detect the use of steganography, which encompasses various methods of hiding messages in apparently ordinary digital images and videos.

It is feared electronic steganography can be used by terrorist organizations to pass along orders or other vital information surreptitiously through images posted on the Internet or sent via e-mail.

The grant for more than $167,000 was awarded to Charles Boncelet, UD professor of electrical and computer engineering, to conduct research in the relatively new field of steganalysis.

Boncelet will work on the project with Lisa Marvel, a UD graduate now employed by the U.S. Army Research Laboratory, and with several graduate students.

Boncelet said steganography is Greek for covered writing, and is a means by which a person can hide the very fact that they are communicating.

In that, it differs from the better-known practice of cryptography, Greek for secret writing, in which a message is purposely garbled and can be understood only by those who have the key to decipher it.

The two forms of communication are not mutually exclusive, Boncelet said, and can be combined. A person can encrypt a message and then hide the fact that they are sending it.

Boncelet previously worked in steganography for the U.S. Army and through this project will begin working in steganalysis, or the development of methods by which to seek out steganography.

A digital image without hidden information

“The work we are doing is in multimedia, with a focus on digital images,” Boncelet said. “You can take an image on your web site and use steganographic techniques to hide a message in the image. The image looks completely ordinary but if you know the key, you can extract the secret message.”

“The object of the research,” Boncelet said, “is to try to figure out how to find steganography in the images.”

The problem is that steganalysis is very difficult because the messages are hidden by design. However, Boncelet said, “when you hide a message in a digital image, you change the image a little bit. If you change the image too much, it gives it away.”

The way to determine any changes to an image, given that the steganalyst does not have the benefit of the original for purposes of comparison, is to use algorithms and very fast computers to look for unusual features in the image.

Boncelet said he believes the research will lead to a novel class of electronic steganography searchers based on image representations that depend on a quality factor, with the long-term goal being automated scanners that can rapidly find likely candidates amongst large numbers of images and videos.

“Assuming the technique we develop is successful, we hope to branch out to video and audio,” Boncelet said, “but right now the focus is on digital images.”

In addition to the research, the project will provide training in steganalysis and intelligence techniques to the students involved.

Boncelet said steganography “is a very big fear for governments,” adding that the security agencies that deal with the technique “worry about terrorists passing messages, or traitors leaking out information from secure sites.”

The same digital image with 5 kilobytes of hidden information added.

After the terrorist attacks of Sept. 11, 2001, there was widespread speculation in the public press that terrorists had used steganography on the Internet to communicate plans. Although those reports were never confirmed, the possibility remains a grave concern.

One of the earliest examples of steganography comes from ancient history, Boncelet said, explaining that a Greek city was surrounded by enemy soldiers and the leader wanted to get a message to his allies to send troops. He selected a slave and shaved his head, tattooing the plea for help on his scalp, then allowed the slave’s hair to grow back over the message. The slave was sent out of the city walls, was captured and released by the enemy troops, and arrived safely with the message.

In World War II, Boncelet said, American soldiers used steganography to provide information on their whereabouts to relatives back home by putting a pinprick on a map. Army censors were forced to pepper letters with hundreds of pinpricks to offset the practice. German spies used steganography in microdots, tiny images of typed pages that could be pasted over periods in seemingly harmless letters.

A benign use of steganography involved the technology of the fledgling television industry of the 1950s, Boncelet said.

“When television first came onto the scene, it was as gray scale, or black and white,” he said. “A movement arose to add color. One school of thought was to devise an entirely new standard, which would make all the black and white sets obsolete. Instead, engineers found a way to hide the color signal so the black and white television did not see that message and could remain in use.”

The NSF grant is for one year and was awarded through the Approaches to Combat Terrorism Program in the Directorate for Mathematical and Physical Sciences, which supports new concepts in basic research and work force development with the potential to contribute to national security.

Article by Neil Thomas
Photo by Kevin Quinlan

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