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From Information Piracy to Digital Fingerprints

Center for Information Forensics Does Digital Detective Work

By Doug Peterson

September 2007

Johnny Depp of Pirates of the Caribbean fame isn’t the only pirate making waves in Hollywood. Digital pirates are pilfering profits from major movie studios by making illegal copies of DVDs and then selling them on the black market.

However, the new Center for Information Forensics at Illinois aims to sink these pirates with an arsenal of information-age weapons. CSL helped start this multidisciplinary, cross-campus center, which is part of the Information Trust Institute.

The 18 researchers who make up the center are using advanced data analysis methods to look for anomalous activities and patterns, discover untrustworthy nodes in networks, and detect tampering with computer hardware, software, and data files.

Digital Fingerprints

One approach under study in the new center is digital fingerprinting, says CSL researcher Pierre Moulin, director of the Center for Information Forensics and professor of electrical and computer engineering. Just as police can track unique fingerprints back to a culprit, it is possible to tag DVDs, CDs, and other recordings with digital fingerprints, which are like serial numbers embedded within the recordings’ data. Illegal copies will carry this digital fingerprint, which can then be traced back to the original owner.

Moulin cites a 2004 case in Hollywood, in which a projector operator was bribed by an Illinois man to make illegal copies of movies before they were released in theaters. Digital fingerprints led investigators back to this digital pirate.

To get around the digital fingerprinting system, two or more people will collude by creating a forgery that combines both of their copies. Using signal processing methods, they can reduce the visibility of the digital fingerprints, Moulin says. But he and other researchers are battling back with techniques that approach the information-theoretic performance limits for digital fingerprinting in the face of collusion.

“The more colluders there are, the harder it is to preserve the digital fingerprints,” he explains. “We’re trying to find strategies that resist more than 100 colluders.”

Photo Tampering

Researchers in the new center are also working in the area of information forensics, in which they develop mathematical methods that detect when a photograph or even a video has been doctored.

A famous example was a Reuters photo, taken of Israeli raids on Beirut’s suburbs in 2006. Photographers noticed what they called obvious manipulation -- the “enhancement” of smoke billowing from destroyed buildings. Someone had used the Photoshop cloning tool to add more smoke to the scene, making it more dramatic -- but less real.

Reuters issued an apology for the manipulation.

Not all doctoring of photos is this obvious, however. So researchers in the Center for Information Forensics are looking for ways to detect mathematically when an image or video has been tampered with.

“The natural statistics of pictures are disturbed when people do this kind of processing,” Moulin says. “If it’s well done, you can’t notice it with your eye. So we’re coming up with a statistical test to detect it.”

Secret Messages

On another front, researchers are finding ways to both hide messages within images and detect secret messages -- “steganography,” as it is known. Some fear, Moulin says, that terrorists and other criminals will be able to communicate covertly by embedding hidden messages within images on the Internet.

On the other hand, secret communication such as this might also allow people who live under oppressive regimes to communicate freely.

“We’re developing algorithms or codes that can embed messages in images,” he says. “But we’re also using statistical analysis to reveal the presence of hidden information.”

The Center for Information Forensics in the Information Trust Institute includes faculty and senior research scientists from CSL, Electrical and Computer Engineering, Computer Science, Beckman Institute, Statistics, Aerospace Engineering, Linguistics, and the National Center for Supercomputing Applications.

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