Quantum key distribution (QKD) permits information-theoretically secure
transmission of digital encryption keys, assuming that the behaviour of the
devices employed for the key exchange can be reliably modelled and predicted.
Remarkably, no assumptions have to be made on the capabilities of an
eavesdropper other than that she is bounded by the laws of Nature, thus making
the security of QKD "unconditional". However, unconditional security is hard to
achieve in practice. For example, any experimental realisation can only collect
finite data samples, leading to vulnerabilities against coherent attacks, the
most general class of attacks, and for some protocols the theoretical proof of
robustness against these attacks is still missing. For these reasons, in the
past many QKD experiments have fallen short of implementing an unconditionally
secure protocol and have instead considered limited attacking capabilities by
the eavesdropper. Here, we explore the security of QKD against coherent attacks
in the most challenging environment: the long-distance transmission of keys. We
demonstrate that the BB84 protocol can provide positive key rates for distances
up to 240 km without multiplexing of conventional signals, and up to 200 km
with multiplexing. Useful key rates can be achieved even for the longest
distances, using practical thermo-electrically cooled single-photon detectors.Comment: 6 pages, 3 figures, supplementary informatio
We present a demonstration of software defined networking (SDN) services utilizing quantum key distribution (QKD) technology, fully integrated with standard telecommunication network connecting production facilities of Telefonica in Madrid. All communications “co-propagate” over the same fiber infrastructure.
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