Re: Quantum Cryptography can not work

"Joseph Ashwood" <ashwood@xxxxxxx> writes:

Combining two posts, since they both cover the same aspects.

"Ben Rudiak-Gould" <br276deleteme@xxxxxxxxx> wrote in message
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Joseph Ashwood wrote:
<robertwessel2@xxxxxxxxx> wrote in message
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QC is link level encryption, not session level.

Right, but in order to connect to a large number of endpoints, it is
necessary to somehow route that link.

The messages that get sent over a quantum-encrypted channel are just
sequences of bits. You can use an ordinary router. I think you're
confusing quantum cryptography with quantum computing.

Quantum Cryptography requires a link between the endpoints in order to send
the photons, this is QC 101. The external messages are an external problem.

You need a link between the endpoints to send any message including this
new post.

You cannot use an ordinary router for this link because there is no physical
link in an ordinary router, you MUST have a physical link, routing this link
is just like routing in the old telephone system, it would have to be

How in the world do you think the packets get from one place to another
with a router? There certainly is a physical link.

significantly faster at switching though to be of any usefulness.

Faster than what?



"Ben Rudiak-Gould" <br276deleteme@xxxxxxxxx> wrote in message
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Joseph Ashwood wrote:
Assuming the cable is a vacuum, the router will require
299792458*lookup_time_in_seconds of cable for each open connection
For a 1 ms router the router would require ~299792 meters of fiber optic
cable for each connection

That's equally true for a classical router, if you use optical delay
lines.

Which is exactly what Quantum Cryptography requires, an optical delay.
But there are much more efficient ways of storing the packet in both the
classical and quantum cases.

In the classic case we can because changing to a different photon or
electron, or switching between them is irrelevant, this allows storage of
the data over the time of the exchange. In the quantum case we cannot change
photons or electrons, so an actual uninterrupted physical link has to exist.

Sure you can. You just cannot copy them so that there are more than one
copy. YOu can however change the qubit stored as a photon for it stored as
an electron spin, to one stored as two levels of an atom, etc.


Classical only requires reproducing an approximation of the signal, quantum
requires the exact signal, it cannot be duplicated.

Agreed, but the router does not need to duplicate it. It just needs to
route it.

Joe


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Relevant Pages

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