Toshiba Research Europe says it has developed two new
technologies to deliver “unconditionally secure” quantum key
distribution (QKD) for network encryption security.
To achieve this, Toshiba has overcome a potential security loophole
in current commercial QKD systems.
In principle, quantum key distribution provides an absolutely
secure means for transmitting secret keys between two parties on
fibre optical networks.
However, the QKD systems developed so far have a vulnerability
which leaves them open to hacking. The weak laser diode used to
generate single photon pulses which carry the quantum keys, will
sometimes generate pulses with multiple photons.
As a result, an eavesdropper could split off one of these extra
photons and measure it, while leaving the other photons in the
pulse undisturbed, thus determining part of the key while remaining
undetected.
Furthermore, an eavesdropper could even determine the entire key,
by blocking the single-photon pulses and allowing only the
multi-photon pulses to travel through the fibre.
Now two solutions to this problem have been found, the first of
which has already been implemented by Toshiba in its own QKD
system.
Toshiba has implemented a new method for QKD, in which the
photon signal pulses are interspersed randomly with a number of
“decoy pulses” to flummox eavesdroppers.
Using the solution, Toshiba has demonstrated a 100-fold increase
in the rate that keys can safely be transmitted securely over a
25km fibre to an average bit rate of 5.5kbit/s – the highest value
to date for a full QKD system, said Toshiba.
This work is part of the EU initiative SECOQC to build a secure
communication network based on QKD.
Dr Andrew Shields, Quantum Information Group leader at Toshiba
Research Europe, said, “Using these new methods for QKD we can
distribute many more secret keys per second, while at the same time
guaranteeing the unconditional security of each. This enables QKD
to be used for a number of important applications such as
encryption of high bandwidth data links.”
The second method, based on nano-technology, will produce even
higher bit rates in the future. Toshiba has created the first
semiconductor diode that can be controlled with electrical signal
input to emit only single photons at a wavelength compatible with
optical fibres. This ‘single photon source’ method eliminates the
problem of multi-photon pulses altogether.
It was developed as part of a DTI funded programme involving the
University of Cambridge, Imperial College London and Toshiba.
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