> allegedly "unhackable" communication networks

they are unhackable using classical methods. So the hacks would be QM based as well (so DefCon will be like QM physicists symposium). Like something along the lines of entangling with (yet not measuring) the signal and performing "shadow" ("counterfactual quantum communication") read of a that signal (entanglement transitivity/swapping, especially if the read/measurement is done after Alice&Bob had already got satisfied with the integrity of the signal as there are also interesting possibilities with that "entanglement in the future affecting the past". Or like this QM analog of NSA Google fiber splitter https://www.extremetech.com/extreme/156673-the-first-quantum... : the photon 4 would be injected back into the channel and Alice and Bob would never know the difference [between the pair 1,4 and the original pair 1,2] while the photon 3 would go into Eve's pocket ).

No, this kind of thing is ruled out by the protocol. There's a theorem called "monogamy of entanglement" which means that two maximally entangled qubits can't also be entangled (or even correlated) with a third. This means that Alice and Bob can guarantee that the key they're agreeing on wasn't intercepted. The theoretical argument is airtight. It doesn't rely on any assumptions about the adversary's computing power, or on whether the adversary has access to a quantum computer. The only way it fails is if physics works significantly differently to how we think it does.

Of course there can still be implementation errors or attacks at the endpoints. The strength of the chain is the strength of the weakest link. But the abstract protocol itself is a very strong link.

They don’t need to hack the network, just turn some people or beat them with rubber hoses.

Obligatory xkcd https://xkcd.com/538/

also Mickens https://www.usenix.org/system/files/1401_08-12_mickens.pdf

Here's a start (hint: they're not "unhackable" nor are they actually "guaranteed by the laws of physics")

https://twitter.com/hashbreaker/status/689115480267816960

https://arxiv.org/abs/1803.04520

Everything that paper says is true, but it's also incredibly obvious. It just points out that it's impossible to rule out side-channel attacks at the endpoints. If Eve has powerful enough equipment then she can just read the secret out of Alice's brain before Alice even types it into her computer. I don't think anyone saying or hearing the claim that quantum protocols are "guaranteed by the laws of physics" understands it to mean that the protocol protects against that kind of attack.

Same way they attack SSL and other cryptographic security systems, I'd suppose.

Via implementation bugs, or backdooring parts of the endpoints, you mean?

Yes! Attack everything around it, and any mistakes using it.

APT the computer hardware of the endpoints.