Comment by hannob | Hacker News Reader

Comment by hannob | Hacker News Reader

There's an important thing that the article fails to mention: Fighting "Quantum with Quantum" might sound nice, but it's not only expensive, it doesn't work.

The idea here is to use so-called Quantum Key Distribution where photons are transmitted over a physical line and the laws of physics guarantee its security.

But there's a problem (ok, there are many problems): Quantum Key Distribution relies on an authenticated channel that is simply assumed to already exists. How do you get that authenticated channel? Nobody knows.

(Apart from that QKD would be hugely expensive, wouldn't work over wifi or mobile connections and would have pretty severe distance limits, which all make a "Quantum Internet" a ridiculous enterprise - but the authenticated channel really kills the whole thing as a solution for Quantum Computer attacks.)

>Quantum Key Distribution relies on an authenticated channel that is simply assumed to already exists. How do you get that authenticated channel

It does already exist, there are several quantum networks already. Though, there are also signs that the first generation may have technological issues. And the entire benefit is that using it will allow you to detect if the channel is authenticated, it does nothing to ensure that it is.

'hannob is referring to the reliance of QKD protocols on "an ordinary public communications channel, assumed to be susceptible to eavesdropping but not to the injection or alteration of messages." [0] This means that, unless your authenticated channel itself cannot be broken using quantum computers, using QKD with it will still not let you do secure post-quantum key exchange. If you have a authenticated channel that can't be broken with quantum computers, how did you implement that without either already having or arriving at a shared secret? (If you already have a way of securely arriving at a shared secret, then what do you need QKD for?)

[0]: at page 177 in http://researcher.watson.ibm.com/researcher/files/us-bennetc...

> How do you get that authenticated channel? Nobody know

Isn't the whole point of these channels that you can detect anyone in the middle? You don't need to assume there's a good channel, you can tell while using it. Perhaps I'm misremembering though, it's been a while since I did this.

That only tells you whether there is someone in the middle, it doesn't tell you that the party on the other end is the party you intend to communicate with.

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