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NIST System Sets Speed Record For Generation of Quantum Keys for ‘Unbreakable’
Encryption
May, 2004.
CONTACT: Laura Ost
(301) 975-4034
The fastest known cryptographic system based on transmission of single
photons—the smallest pulses of light—has been demonstrated
by a team at the Commerce Department’s National Institute of Standards
and Technology (NIST). The transmissions cannot be intercepted without
detection, so that messages encrypted with the system can be kept secret.
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| Physicist Joshua Bienfang sets up the NIST quantum key distribution
system to receive a string of photons from colleagues stationed
on the top floor of the NIST Administration Building (shown in the
background.) The black instrument on the left is an 8-inch telescope
used in collecting the incoming photons.
Photo by Gail Porter/NIST
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The NIST “quantum key distribution” (QKD) system transmits
a stream of individual photons to generate a verifiably secret key—a
random series of digital bits, each representing 0 or 1, used to encrypt
messages—at a rate of 1 million bits per second (bps). This rate
is about 100 times faster than previously reported systems of this type.
The demonstration, described in the May 3 issue of Optics Express,
is the first major reported result from a new NIST testbed built to
demonstrate quantum communications technologies and cryptographic key
distribution. The testbed provides a measurement and standards infrastructure
for research, testing, calibrations and technology development. Scientists
tested the QKD system by generating an encryption key that could be
sent back and forth between two NIST buildings that are 730 meters apart.
They are using the testbed to develop data-handling techniques associated
with this type of encryption.
Acadia Optronics LLC of Rockville, Md., consulted on the system design
and hardware. Partial funding for the project was provided by the Defense
Advanced Research Projects Agency.
Quantum systems—exploiting the laws of quantum mechanics—are
expected to provide the next big advance in data encryption. The beauty
of quantum key distribution is its sensitivity to measurements made
by an eavesdropper. This sensitivity makes it possible to ensure the
secrecy of the key and, hence, the encrypted message. The keys are generated
by transmitting single photons that are polarized, or oriented, in one
of four possible ways. An eavesdropper reading the transmission causes
detectable changes at the receiver. When such changes are observed,
the associated key is not used for encryption.
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Alan Mink works on a programmable printed circuit board used
to process data for the new NIST quantum key distribution system.
©Robert Rathe
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Compared to previously described QKD systems, the major difference
in the NIST system is the way it identifies a photon from the sender
among a large number of photons from other sources, such as the sun.
To make this distinction, scientists time-stamp the QKD photons, then
look for them only when one is expected to arrive.
“To be effective, this observation time has to be very short,”
says NIST physicist Joshua Bienfang. “But the more often you can
make these very brief observations, then the faster you can generate
keys. We have adapted some techniques used in high-speed telecommunications
to increase significantly the rate at which we can look for photons.”
The NIST team has packaged data-handling electronics operating in the
gigahertz (1 billion bits per second) range in a pair of programmable
printed circuited boards that plug into standard PCs. Photon losses
caused by imperfections in the photon sources and detectors, optics,
and procedures reduce the key generation rate. However, 1 million bps
makes QKD practical for a variety of new applications, such as large
network distributions or streaming encrypted video.
“We are processing data much faster with this hardware than can
currently be done with software,” says NIST electrical engineer
Alan Mink. “You would need a computer processing at more than 100
GHz (about 50 times faster than current PCs) to do it with software
and you still couldn’t do it fast enough because the operating
system would slow you down.”
The NIST quantum system uses an infrared laser to generate the photons
and telescopes with 8-inch mirrors to send and receive the photons over
the air. The data are processed in real time by printed circuit boards
designed and built at NIST, so that a computer produces ready-made keys.
NIST researchers also developed a high-speed approach to error correction.
Further research is planned to improve the system, primarily by addressing
the need for faster photon detectors, the principal barrier to the development
of practical systems for more widespread use. The group plans to incorporate
NIST-developed photon sources and detectors. More information about
NIST’s quantum information program can be found at http://qubit.nist.gov/.
As a non-regulatory agency of the U.S. Department of Commerce’s
Technology Administration, NIST develops and promotes measurement, standards
and technology to enhance productivity, facilitate trade and improve
the quality of life.
For further information on quantum cryptography see:
http://www.nist.gov/public_affairs/releases/quantumkeys_background.htm
*Optics Express is the online rapid publication journal of the Optical
Society of America. See: http://www.opticsexpress.org/.
Reporters/Editors: For high-resolution files of the photos on this
page contact Gail Porter, (301) 975-3392.
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