Quantum cryptography


in Geek stuff, Internet matters, Security

In theory, quantum cryptography (mentioned before is as good as a one time pad, without the need for a secure channel through which to exchange keys. Potentially, it could also employ quantum phenomena to verify that nobody is eavesdropping.

In practice – as with all cryptographic systems – there are weaknesses to be exploited. One known attack exploits a weakness in some sorts of photon detector. Another works by manipulating synchronization signals.

Quantum cryptography may well have some useful applications, but people who expect it to be foolproof and completely secure probably aren’t thinking too well.

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{ 2 comments… read them below or add one }

. July 2, 2013 at 2:18 pm

A third project, organised by Jane Nordholt of Los Alamos National Laboratory, has just demonstrated how a pocket-sized QKD transmitter called the QKarD can secure signals sent over public data networks to control smart electricity grids. Smart grids balance demand and supply so that electricity can be distributed more efficiently. This requires constant monitoring of the voltage, current and frequency of the grid in lots of different places—and the rapid transmission of the results to control centres. That transmission, however, also needs to be secure in case someone malicious wants to bring the system down.

. October 7, 2013 at 2:57 pm

Unbreakable cryptography
The devil and the details
Quantum cryptography has yet to deliver a truly unbreakable way of sending messages. Quantum entanglement may change that

Allison Rubenok and her colleagues at the University of Calgary, in Alberta, and Liu Yang and Chen Tengyun, from the University of Science and Technology of China, use yet another approach. Each group introduces a third party who sits between Alice and Bob.

In this scheme, rather than creating and sending entangled photons, Alice and Bob begin by polarising their light pulses at random. Each then sends his or her pulse, whose polarisation is known only to the sender, to the third party, who performs a variant of the Bell test on the two incoming signals. The outcome is successful for those combinations of photons from Alice and Bob that are in the same quantum state. These outcomes do not need to be secret: once publicly announced, they allow Bob and Alice to pick the sequence of bits associated with them as their private encryption key. Crucially, for complicated reasons that have to do with the nature of the protocol, this scheme does not require near-perfect detectors.

Moreover, as the two groups report in the latest issue of Physical Review Letters, it works even if the connecting optical fibres become long enough to be of practical use. Dr Rubenok and her team have tested their version of the scheme on a spool of optical fibre more than 80km (50 miles) long, and also on 18km of working cable installed in Calgary. Dr Liu and Dr Chen have run it successfully over a link 50km long.

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