ZME Science: Yes, a quantum internet is possible, new study shows

Peter Fairbrother peter at
Mon Dec 31 16:15:20 PST 2018

On 31/12/18 00:50, Punk wrote:
> On Sun, 30 Dec 2018 22:21:06 +0000 (UTC)
> jim bell <jdb10987 at> wrote:
>> ZME Science: Yes, a quantum internet is possible, new study shows.
> 	So what happens when a 'quantum' link used to send keys is
> 	tapped? Does the key still get through?

Yes, but.

Initially it was thought that cloning the signal (as required for 
tapping it) is impossible due to the no-cloning theorem, part of quantum 

Therein would lie the untappable nature of Quantum links. Physics itself 
would protect you.

However it was later realised that the no-cloning theorem only says you 
can't clone a quantum state perfectly - it doesn't say you can't clone 
it at all.

There are several techniques which can be used for partial cloning, some 
such as the well-known 1->2UQC have hard theoretical limits of 5/6 
perfection - ie 5 photons in 6 can be cloned.

Others have higher limits. I think there is even one which doesn't have 
any theoretical limits apart from "not absolutely perfect", but these 
are harder to implement.

While it is possible to design a quantum key exchange machine to defeat 
1->2UQC cloning attacks by taking advantage of the statistical 
limitations of the 1->2UQC cloning process, as far as I am aware 
(admittedly not very far) none of the machines in existence do so.

Plus, a secure authenticated side-channel is required to prevent MITM 

Quantum cryptography is not very useful for anything (except maybe 
getting research funding).

Happy New Year to all!

Peter Fairbrother

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