[hannob]

So-called Quantum Cryptography is largely snake oil. The most important things you need to know about it is that:

* In order to do QC you need an authenticated channel first. QC proponents hardly mention that or try to obscure it, but it basically means you can't have QC unless you already have some other secure cryptography.

* QC has severe practical limits. It needs a point to point connection capable of sending physical particles. That means: No Wifi, no mobile Internet and no connections over large distances. Given that these people recently started talking about a "Quantum Internet" makes this simply ridiculous.

[jpt4]

Of the first point I shall plead Wittgenstein and not speak, but as regards the second: In what way are photons, the medium of wireless telecommunication, not physical particles? In what way are, indirect connections not decomposable into multiple direct connections (broadcast vs. point-to-point is a more robust difference, I agree)?

[marcosdumay]

For QC to work, the receiver must receive the exact same photons the transmitter created. Those photons can not be tampered with, what means they can not be relayed, or reflected by most surfaces.

[bogomipz]

Is there a working and practical implementation somewhere? I was under the impression it wasn't practical yet.

[hannob]

You can buy it: http://www.idquantique.com/

It's probably insecure (these things get broken regularly), not practical for any real use case and total obvious nonsense to buy it, but I think there are some banks who thought they have some money leftover that they'd sink in such devices.