By Stephen Leahy
Fingerprints aren't just for fingers anymore. Now, they could be an
important new tool for fighting document forgery.
All paper, as well as plastic credit and debit cards, bears a unique
"fingerprint" of microscopic surface imperfections. According to
Russell Cowburn, professor of nanotechnology at Imperial College
London, detecting these unique patterns is easy to do with a portable
And it's cheap, too: "Our field scanners could be
manufactured for $1,000 or less (when made) in volume," said Cowburn.
The detection process makes use of the optical phenomenon known as
laser speckle. Light coming from a focused laser is coherent, or in
phase, but when it strikes a microscopically rough surface like a
piece of paper, the light is scattered, producing a pattern of light
and dark "speckles." The scanner's photodetectors digitize and record
According to Cowburn's research, as published July 28 in the journal
Nature, the unique speckle pattern of a sheet of paper remains
recognizable even after crunching the paper into a ball, soaking it in
water, baking it at 180 degrees Celsius (350 degrees Fahrenheit) for
30 minutes, scrubbing it with an abrasive cleaning pad or scribbling
over it with a big black marker.
A cross-correlation algorithm that assesses the degree of similarity
between the base-line scan and the new scan allows the paper's
identity to be verified. The odds of two pieces of paper having
similar patterns are greater than 1,000 to one.
These fingerprints raise the possibility of securing documents without
resorting to controversial solutions like RFID tags. In the future,
every passport, driver's license and birth certificate could be
scanned for its unique speckle pattern by the issuing agency. Portable
scanners at border crossings or police stations would read the pattern
on the document in question and match it to the baseline database. A
standard desktop PC could check 10 million entries per second.
This could put document forgers around the world out of business.
"There is no known manufacturing process for copying surface
imperfections at the necessary level of precision," said Cowburn.
"The beauty of this system is that there is no need to modify the item
being protected in any way with tags, chips or inks," he said.
But it's still not foolproof. This sort of security would not have
prevented the 9/11 terrorists from obtaining their legal Virginia
driver's licenses with false information, said Nick Fadziewicz, an
expert on security at Comter Systems. Eleven of the terrorists
successfully obtained those licenses using false information. Many
states, including Virginia, now have much tougher requirements.
"There is no one solution for security," said Fadziewicz. "The goal is
to put in enough strong security measures to minimize the (potential)
to create fake documents."
It's also important to balance a security system's benefits with its
costs and any resulting inconvenience to the general public, he said.
Other attempts to secure documents like passports have met with
controversy. Many have likened the State Department's plan to embed
RFID chips in all new passports this year to installing homing devices
for high-tech muggers, identity thieves and even terrorists. Unauthor-
ized persons could read or "skim" the information from the RFID chip
and obtain personal data.
In late June, the State Department announced that new passports will
have a metallic lining to prevent unauthorized reading of the tags.
Bill Scannell, a publicist and civil liberties activist, strongly
opposes RFID technology on privacy and other grounds. He said document
identification using speckle patterns has the advantage of not
collecting or broadcasting personal information. But there may be
issues regarding on-the-ground implementation and overall cost.
"We're spending billions on new, ever-more-complex security technology
... At what point does this become stupid?"
Copyright 2005, Lycos, Inc. Lycos is a registered trademark of
Carnegie Mellon University.
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