First Secure Quantum Crypto Network Up and Running

John Lam was one of many readers to send in news that on Thursday, "at a conference in Vienna, Austria, as reported by the BBC, a European Community science working group built a quantum backbone using 200-km of standard commercial optical fiber running among seven sites and successfully demonstrated the first secure quantum cryptographic key distribution network. In addition, each of the seven links used a different kind of quantum encryption, demonstrating interoperability between the technologies. To paraphrase, the project focused on the trusted repeater paradigm and developed an architecture allowing seamless integration of heterogeneous quantum-key distribution-link devices in a unified framework. Network node-modules managing all classical communication tasks provide the underlying quantum devices with authentic classical channels. The node-module architecture uses a layered model to provision network-wide, end-to-end, provably secure key distribution."

Comments

Re:Teleportation?

[IceCreamGuy]

it's only Photons that have been 'tele-ported'

It is actually not a particle like a photon, but only information that is teleported. Just in case your next question is "doesn't this mean we can communicate at the speed of light?" you must have a classical information channel as well in order to make sense of the teleported information.

Secure Key exchange.

[locofungus]

I heard something about this on the radio last night (wasn't paying full attention).

But they were talking about quantum key exchange. Assuming that they're then using a standard symmetric key to encrypt the link it's still theoretically breakable, just the key exchange that isn't.

If they're quantum encrypting all the data then that's pretty astonishing - they were talking about video-conferencing so they need a reasonable bit rate and the fidelity rate has to be above 5/6[1] otherwise the link might be vulnerable to a quantum cloning attack.

[1] Assuming the best attack is a universal quantum cloning machine. The maximum theoretical fidelity isn't known for most non-universal quantum cloning machines (but is trivially known for some - e.g. 3/4 for a naive measure and retransmit). I don't know whether it's possible to prove that the 5/6 is a sufficient lower bound on the fidelity.

Tim.

Re:Secure Key exchange.

[Bengie]

"[...]Assuming that they're then using a standard symmetric key to encrypt the link it's still theoretically breakable[...]" depends on what you mean by "theoretically". According to my cousins professor in his Computer Science Encrption course, if you had a *perfect* 256bit symmetric key encryption, if you counted just bit flips and no other inefficiency of the system, on average it would take more energy to break the key than there is usable energy in the known universe. and from what I've read about quantum computing, a quantum computer is only about 2xs faster than a regularcomputer at breaking symmetric key encrtion, so no hope there; but they really shine on asymetric sinceyou already have part of the key. All we need is a 512bit symetic key and you're screwed for theory unless there's a HUGE mathematical flaw in it. And most of the known flaws in the current AES are theorectical and haven't been proven, that I know of.

Re:Not so sercure then

[david_thornley]

Yeah, but the same crypto that allows digital signatures also allows secure key exchange.

In other words, although this is an impressive achievement, it isn't clear to me that there's any practical application as yet. Particularly when we consider that modern crypto is almost certainly secure, so that intercepting the bits en route is pointless, and that you don't need crypto over a physically secure route.

Quantum computation and communications may well be very useful some year, but 2008 isn't it.