Chaotic lasers lock messages
Technology Research News
People separated by distance can exchange
a secure message by first encrypting it using a random mathematical key.
The challenge is ensuring that the intended recipient -- and no one else
-- can get a copy of the key required to decrypt the message.
Researchers from Advanced Telecommunications Research Institute
International (ATR) in Japan have found a way for two people in different
locations to work out a cryptographic key using the signal from the rapidly
and randomly fluctuating light signal of a chaotic laser.
The method allows a sender and receiver to exchange and compare
parts of a chaotic signal in order to identify portions that they can
use to generate a cryptographic key.
The method could be used to transmit secure keys through space
or over fiber-optic lines that are tens or hundreds of kilometers long.
The method could also be used with chaotic radio signals, which could
lead to cheap, general-purpose encryption systems, said Peter Davis, a
senior researcher at Advanced Telecommunications Research Institute International.
To make a key, a sender and receiver independently record random
sections of the chaotic signal, select marked portions that delineate
segments that can be used to make a key, then compare marks over an unsecure
channel to identify a string of segments they recorded in common. The
security comes from the very long odds against an eavesdropper being able
to record all the segments that the sender and receiver recorded in common.
A chaotic semiconductor laser signal generates a very large amount
of information. The signal is analog, unlike the on-off pulses normally
used to send digital information over fiber-optic lines. "State-of-the-art
semiconductor lasers can generate chaotic signals equivalent to one gigabyte
of random bits per second, and potentially at least 10 times more than
this," said Davis.
A gigabyte, or one billion bytes, is equivalent to the information
in a 10-meter high stack of books, or a little more than a fifth of a
DVD's worth of data.
The researchers showed they could tune the system's variables
to assure that the eavesdropper had less than a one in a trillion trillion
trillion trillion trillion trillion trillion trillion -- that's a one
followed by 100 zeros -- chance of acquiring a key composed of 100 segments
shared between the sender and receiver.
The eavesdropper's chances improve with better recording equipment,
but only so far. Put 100 lasers together, and it becomes even more difficult
to make a complete record of the chaotic signal. "We could use an array
of 100 lasers to generate 100 gigabytes per second, or 360 terabytes of
data per hour," said Davis. In comparison, the printed material contained
in the Library of Congress contains about 10 terabytes.
Three hundred sixty terabytes of data per hour is "not only...
a huge volume, but the processing and communication bandwidth required
to sample and record at 100 gigabytes is formidable," Davis said.
As time goes on, progress in laser chaos technologies should lead
to even higher random bit rates. Rates could reach 100 gigabits per second
for a single laser in the next 10 years, he said.
There has been a lot of research in recent years into using chaotic
laser-generated waveforms for encryption, but most of the work has focused
on hiding data within chaotic waveforms. The security comes from the long
odds against an eavesdropper being able to separate the data from the
chaotic noise of the signal. The drawback to this approach is that it
assumes the sender and receiver already have the key necessary to extract
the data, according to Davis.
Because the signal the researchers use to generate their keys
is analog, its transmission is limited to tens or hundreds of kilometers.
"Hence we envision its use mainly in local or special-purpose analog fiber
lines," said Davis.
The signal could also be transmitted through space using narrow
or wide light beams. Narrow beams carry more data and are more difficult
to intercept. Wide beams are easier to receive while moving around, said
In principle the researchers' scheme could be used with any type
of chaotic signal source. The researchers are looking into microwave and
millimeterwave radio sources, said Davis.
Special purpose applications like secure networks for intelligent
buildings could be practical in two to five years; less expensive general-purpose
systems and schemes that require radio signal sources could become practical
in 5 to 10 years, according to the researchers.
Davis' research colleagues were Atsushi Uchida of ATR and S. Itaya
of Abel Systems Inc. in Japan. The work appeared in the October 13, 2003
issue of Applied Physics Letters. The research was funded by the Japanese
Telecommunication Advancement Organization (TAO) and Abel Systems Inc.
Timeline: 5-10 years
Funding: Corporate; Government
TRN Categories: Cryptography and Security; Optical Computing,
Optoelectronics and Photonics;Telecommunications
Story Type: News
Related Elements: Technical paper, "Generation of Information
Theoretic Secure Keys using a Chaotic Semiconductor Laser," Applied Physics
Letters, October 13, 2003
December 3/10, 2003
Biochip puts it all together
DNA assembles nanotube
Chaotic lasers lock messages
give painless shots
Molecule makes two-step
Spin material handles
Research News Roundup
Research Watch blog
View from the High Ground Q&A
How It Works
News | Blog
Buy an ad link