Toshiba Research Europe says it has developed two new technologies to deliver “unconditionally secure” quantum key distribution (QKD) for network encryption security.
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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 5.5kbits/sec – 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.
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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Read more on quantum crypotography: www.cs.dartmouth.edu/~jford/crypto.html
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