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Code for ‘Unbreakable’ Quantum Encryption Generated at Record
Speed over Fiber
April 18, 2006
CONTACT: Laura Ost
(301) 975-4034
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Gaithersburg, Md.—Raw code for “unbreakable” encryption,
based on the principles of quantum physics, has been generated at record
speed over optical fiber at the Commerce Department’s National
Institute of Standards and Technology (NIST). The work, reported today
at the SPIE Defense & Security Symposium in Orlando, Fla.,* is a
step toward using conventional high-speed networks such as broadband
Internet and local-area networks to transmit ultra-secure video for
applications such as surveillance.
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NIST physicist Xiao Tang and colleagues have developed a quantum
communications system that uses single photons to produce a "raw"
encryption key at the rate of 4 million bits per second.
Image credit: © Robert Rathe
For a high-resolution version of this photo contact Gail
Porter.
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The NIST quantum key distribution (QKD) system uses single photons,
the smallest particles of light, in different orientations to produce
a continuous binary code, or "key," for encrypting information.
The rules of quantum mechanics ensure that anyone intercepting the key
is detected, thus providing highly secure key exchange. The laboratory
system produced this “raw” key at a rate of more than 4 million
bits per second (4 million bps) over 1 kilometer (km) of optical fiber,
twice the speed of NIST’s previous record, reported just last month.**
The system also worked successfully, although more slowly, over 4 km
of fiber.
The record speed was achieved with an error rate of only 3.6 percent,
considered very low. The next step will be to process the raw key, using
NIST-developed methods for correcting errors and increasing privacy,
to generate "secret" key at about half the original speed,
or about 2 million bps.
NIST has previously encrypted, transmitted and decrypted Web quality
streaming video using secret keys generated at 1 million bps in a 1-km
fiber QKD system using a slightly different quantum encoding method.***
Using the same methods for correcting errors and improving privacy with
the key generated twice as fast or faster should allow real-time encryption
and decryption of video signals at a resolution higher than Web quality,
according to NIST physicist Xiao Tang, lead author of the paper.
“This is all part of our effort to build a prototype high-speed
quantum network in our lab,” says Tang. “When it is completed,
we will be able to view QKD-secured video signals sent by two cameras
at different locations. Such a system becomes a QKD-secured surveillance
network."
Applications for high-speed QKD might include distribution of sensitive
remote video, such as satellite imagery, or commercially valuable material
such as intellectual property, or confidential healthcare and financial
data. In addition, high-volume secure communications are needed for
military operations to service large numbers of users simultaneously
and provide multimedia capabilities as well as database access.
NIST is among a number of laboratories and companies around the world
developing QKD systems, which are expected to provide the next generation
of data security. Conventional encryption is typically based on mathematical
complexity and may be broken given sufficiently powerful computers and
enough time. In contrast, QKD produces encryption codes based on the
quantum states of individual photons and is considered “verifiably
secure.” Under the principles of quantum physics, measuring a photon's
quantum state destroys that state. QKD systems are specifically designed
so that eavesdropping causes detectable changes in the system.
NIST systems are much faster, although operating over shorter distances,
than previously reported QKD systems developed by other organizations.
High-speed transmission is necessary for widespread practical use of
quantum encryption over broadband networks. The NIST fiber QKD system
was designed by physicists, computer scientists and mathematicians and
is part of a testbed for demonstrating and measuring the performance
of quantum communication technologies. NIST has used the testbed to
demonstrate QKD in both a fiber-based system and an optical wireless
system operating between two NIST buildings.
The NIST fiber QKD system has two channels operating over optical fibers
that are wrapped around a spool between two personal computers in a
laboratory. The photons are sent in different quantum states, or orientations
of their electric field, representing 0 and 1. The system compensates
for temperature changes and vibration, which could affect performance,
with a NIST-designed module that automatically adjusts photon orientation
on a time schedule. More extreme environmental changes are likely to
occur in fibers buried or suspended outdoors as in telephone networks;
the researchers plan to test a fiber QKD system in the field in the
future.
After raw key is generated and processed, the secret key is used to
encrypt and decrypt video signals transmitted over the Internet between
two computers in the same laboratory. The high speed of the system enables
use of the most secure cipher known for ensuring the privacy of a communications
channel, in which one secret key bit, known only to the communicating
parties, is used only once to encrypt one video bit (or pixel). Compressed
video has been encrypted, transmitted and decrypted at a rate of 30
frames per second, sufficient for smooth streaming images, in Web-quality
resolution, 320 by 240 pixels per frame.
The work is supported in part by the Defense Advanced Research Projects
Agency.
As a non-regulatory agency of the U.S. Department of Commerce’s
Technology Administration, NIST promotes U.S. innovation and industrial
competitiveness by advancing measurement science, standards, and technology
in ways that enhance economic security and improve our quality of life.
* X. Tang, L. Ma, A. Mink, A. Nakassis, H. Xu, B. Hershman, J. Bienfang,
R.F. Boisvert, C. Clark, D. Su and C. Williams. 2006. Auto-compensated,
polarization coding, fiber-based quantum key distribution system operating
at sifted-key rate over 4Mbit/s. Presented April 18 at the SPIE Defense
& Security Symposium, Orlando, Fla.
** X. Tang, L. Ma, A. Mink, A. Nakassis, H. Xu, B. Hershman, J.C. Bienfang,
D. Su, R. Boisvert, C.W. Clark and C.J. Williams. 2005. Experimental
study of high speed polarization-coding quantum key distribution with
sifted-key rates over Mbit/s. Optics Express. Posted online March 20.
***A. Mink, X. Tang, L. Ma, A. Nakassis, B. Hershman, J. Bienfang,
D. Su, R. F. Boisvert, C. Clark, and C. Williams. 2006. High Speed Quantum
Key Distribution System Supports One-Time Pad Encryption of Real-Time
Video. Presented April 18 at the SPIE Defense & Security Symposium,
Orlando, Fla.
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