Scientists Find Cheaper Way to Ensure Internet Security
Scientists
at Toshiba and Cambridge University have perfected a technique that offers a
less expensive way to ensure the security of the high-speed fiber optic cables
that are the backbone of the modern Internet.
The
research, which will be published Tuesday in the science journal Physical
Review X, describes a technique for making infinitesimally short time
measurements needed to capture pulses of quantum light hidden in streams of
billions of photons transmitted each second in data networks. Scientists used
an advanced photo detector to extract weak photons from the torrents of light
pulses carried by fiber optic cables, making it possible to safely distribute
secret keys necessary to scramble data over distances up to 56 miles.
Such
data scrambling systems will most likely be used first for government
communications systems for national security. But they will also be valuable
for protecting financial data and ultimately all information transmitted over
the Internet.
The
approach is based on quantum physics, which offers the ability to exchange
information in a way that the act of eavesdropping on the communication would
be immediately apparent. The achievement requires the ability to reliably
measure a remarkably small window of time to capture a pulse of light, in this
case lasting just 50 picoseconds — the time it takes light to travel 15
millimeters.
The
secure exchange of encryption keys used to scramble and unscramble data is one
of the most vexing aspects of modern cryptography. Public key cryptography uses
a key that is publicly distributed and a related secret key that is held
privately, allowing two people who have never met physically to securely
exchange information. But such systems have a number of vulnerabilities,
including potentially to computers powerful enough to decode data protected by
mathematical formulas.
If
it is possible to reliably exchange secret keys, it is possible to use an
encryption system known as a one-time pad, one of the most secure forms.
Several commercially available quantum key distribution systems exist, but they
rely on the necessity of transmitting the quantum key separately from
communication data, frequently in a separate optical fiber, according to Andrew
J. Shields, one of the authors of the paper and the assistant managing director
for Toshiba Research Europe. This adds cost and complexity to the cryptography
systems used to protect the high-speed information that flows over fiber optic
networks.
Weaving
quantum information into conventional networking data will lower the cost and
simplify the task of coding and decoding the data, making quantum key distribution
systems more attractive for commercial data networks, the authors said. Modern
optical data networking systems increase capacity by transmitting multiple data
streams simultaneously in different colors of light. The Toshiba-Cambridge
system sends the quantum information over the same fiber, but isolates it in
its own frequency.
“We
can pick out the quantum photons from the scattered light using their expected
arrival time at the detector,” Dr. Shields said. “The quantum signals hit the
detector at precisely known times — everyone nanosecond, while the arrival time
of the scattered light is random.”
Despite
their ability to carry prodigious amounts of data, fiber-optic cables are also
highly insecure. An eavesdropper needs only to bend a cable and expose the
fiber, Dr. Shields said. It is then possible to capture light that leaks from
the cable and convert it into digital ones and zeros.
“The
laws of quantum physics tell us that if someone tries to measure those single
photons, that measurement disturbs their state and it causes errors in the
information carried by the single photon,” he said. “By measuring the error
rate in the secret key, we can determine whether there has been any
eavesdropping in the fiber and in that way directly test the secrecy of each
key.”
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