[ikari_pl]

I'd prefer @ziofill to answer, but I think:

- security - if we use quantum entanglement/teleportation to the extent I've read about how it works, then even if you still need a fiber optic cable connecting the two parties, the data is unreadable if you're not looking at physically the same wave/photons, meaning that man in the middle attack (like the ones with bending an optic cable to break it's internal reflection) is literally impossible. The data in the middle would not be readable without the receiving end entangled device, and the other side would immediately know about the attack, because an identical signal would not be readable either, as it's not the same signal anymore.

- I think the ultimate promise is transferring data without a physical link of any kind in-between. Connect two atoms, manipulate one, read the other - like ansibles in LeGuin/O.S.Card fiction. Instant interplanetary communication (which, I think, fucks up the idea of time too?)

[tsimionescu]

The first one helps with physical attacks on the wire. Not a common issue that people worry about, since there are so many boxes in between that are easier to compromise that it's rarely a significant security increase if you know the wire is perfectly secure.

The second is just wrong. It is well known and proven that it's impossible to send information via quantum entanglement. It's true that there are some interpretations of QM where the wave function of the entangled pair collapses instantly the moment one side of the pair is measured. But there is no version of QM where manipulating one side of the pair has any effect whatsoever on the other, except for measurement collapsing the quantum superposition into a random classical state.

The best classical intuition for how entanglement works is that two entangled particles are like two gloves from a pair. If you put them in boxes and separate them, when someone opens a box and finds the left glove, they instantly find out that the other person has the right glove. The difference with quantum entanglement is simply that the universe only decides which glove is which when you open the box, before that they are both in a mix of the states. This makes statistical properties measurably different if you send many pairs of gloves and look at how many times certain things match.

But there really is nothing that you can do with a pair of entangled particles that you couldn't do with the pair of gloves.

I should note for completeness that, because of the different statistical properties, there is a way to send slightly more information using entangled pairs than you can with classical particles. I believe you can send 1.5 bits of information per particle, but I don't remember the exact number. This means that a quantum internet could have higher throughput at the same transmit power, which would have some relevance for very long distance wireless communication, such as communicating with a space probe.

[seanhunter]

People have dealt with the second one in sibling comments but I somewhat doubt the first one is true when you take into account sidechannel attacks on the encoding and decoding part of the transmission.

Yes I get through quantum magic you can theoretically tell if your secret has been intercepted in the quantum state because it would cause a wave form collapse but the wave form wouldn't collapse if they were listening in to your quantum computer squeaking and buzzing and decoding those noises or timings or reading its heat signature etc, or getting your operator drunk and finding out their dog's name or partner's birthday and using it as their password, or kidnapping them and hitting them with things until they voluntarily give you their password etc. All those types of attacks would still work and still be just as undetectable as they are in classical encryption. ie all the most effective forms of attack are still just as effective in a quantum case.

I think it's a very interesting area of research but this whole idea of uncrackable codes is a stretch.

[knoke]

As far as In understand it (not very much) you can listen in on the transmitted keys, but the interaction can be statistically(!) measured and suspicious bits can me omitted (the wiki is quite comprehensible: https://en.wikipedia.org/wiki/Quantum_key_distribution?wprov...). There are different protocols, some more and some less quantum and most rely on classical, encrypted channels and trusted nodes in addition to the quantum channels.

One thing is for sure: you can’t send information faster than light with this or any other kind of quantum communication as two entangled qubits are basically two RNGs that are correlated. You’d just get noise without an additional classical, not FTL, data link (please, somebody with expertise: help!)

[fi358]

As far as I know, they still need classical encryption methods (with something like shared secret key or public key for authentication) to detect active man in the middle attacks where the attacker prevents the parties connecting to each other and then pretending to both parties to be the other party by creating his own "messages" as if they came from the other party. Or at least to have some kind of additional trusted physical medium where it is impossible to prevent the parties communicating directly, capturing their "messages" and then sending your own modified "messages" instead -- perhaps based on some kind of timing etc.

And if you still have to rely to classical encryption methods to make sure you know the identity of the other party (to prevent active man in the middle attack), why not just use classical encryption methods for everything else as well, instead of using quantum key distribution?

[ko27]

You don't need "classical encryption" for quantum key distribution. With QKD you can provably detect if a MITM attack happened. With classical methods you can never be 100% sure, although how much of that matters in practice is another question.

[bawolff]

> You don't need "classical encryption" for quantum key distribution. With QKD you can provably detect if a MITM attack happened.

This is incorrect. QKD can detect passive mitm only. It cannot detect an active mitm.

Which is the main reason its overhyped, since as cool as QKD is, you still need active mitm prevention, so you have to rely on classical crypto anyways.

[HuangYuSan]

No, this does not work. You can both read the same random data (which can be used for generating encryption keys), but not transfer any data.