Researchers trace documents by fingerprinting printers

Source: EE Times
Date: October 13, 2004
Writer: Gregg Keizer
Original Link

MANHASSET, N.Y. - A trio of researchers at Purdue University announced Wednesday (Oct. 13) that they've come up with a way for authorities to trace documents back to the printer that put them on paper, a possible boon to anti-counterfeiting and anti-terrorism efforts. The researchers - Jan Allebach, Edward Delp and George Chui - collaborated on the research, which was funded by the National Science Foundation and supported in part by the U.S. Secret Service, the law enforcement agency largely responsible for battling counterfeiters.

"The first method uses the intrinsic 'signatures,' so to speak, of a printer manufacturer's machines and models within that maker's line," said Jan Allebach, a Purdue professor of electrical and computer engineering.

Using specialized software they developed, the Purdue researchers can spot slight variations in printed characters created as a laser printer's photoconductor drum rotates inside the device.

"Because of variability in printers, the drum does not rotate at a constant speed," said Allebach. "If the drum slows down a little bit, you get print [that] looks a little dark. Where the drum speeds up, you get print [that] looks a little light."

Because every printer has its own unique pattern of this "banding," authorities can use the imperfections to track a document to the printer brand and model within that brand. "Basically, it's like a fingerprint of the printer," said Allebach.

So far, however, that fingerprint isn't specific enough to tell, say, one Hewlett-Packard Color LaserJet 3500 from another. In part, that's because the banding changes when the toner cartridge is changed.

To solve that problem and put a unique fingerprint on every printer, Allebach and his colleagues have developed software that would put one in every printer's firmware. The software would manipulate the printer's laser to artificially embed bands of difference that are too fine to detect with the naked eye, but can be seen under close analysis.

"We don't know if printer manufacturers would do this voluntarily," said Allebach, "since it would add a cost to the printer, albeit a small one. But printer makers are already doing some things to prevent counterfeiting," and this would simply be one more.

The Secret Service is interested, of course, because counterfeiters are increasing going digital to scan currency, then reproduce it on color laser printers. Other criminals, including forgers, use the same techniques to produce false documents such as passports.

"I can see this as a method of authenticating other high value documents," said Allebach, "such as stock certificates. And it obviously has some uses in tracking terrorists that produce printed documents."

Using the Purdue techniques, investigators might be able to trace documents to a country or region, added Allebach.

"Another bonus is that this would be very difficult to hack, since it's not in the software driver or in the file to be printed," he said of the 'fingerprint.' "It's down inside the hardware, where it's tough to get at."

The trio is broadening its research from laser printers to include the more common, and less expensive, inkjet printers. A wide variety of characteristics, including the paper-moving mechanism as well as variations in ink dot sizes or patterns, said Allebach, should give them plenty to use to 'print' those printers, too.