You probably know more than me.
I know a little about quantum mechanics, and next to nothing about cryptography.
Explain how you can have a photon associated with the transmitted, if you are not connected directly to the photon transmission channel?
And if you hold in your hand a smartphone that is connected to the Internet via 3,4,5-G, then how will you have a coupled photon?
Micius has demonstrated QKD wirelessly via satellite. There have been demonstrations using traditional fibre-optic lines, but the entangled state is more vulnerable to collapse using this approach, so satellite may be the better option.
A pair of entangled photons is generated using an interferometer, and one photon is sent to each party in the communication. If in the Micius example you can communicate with the satellite, then you can receive the photon.
They aim to have a global quantum network in place by 2030. I have no opinion on whether or not 2030 is realistic.
If in a symmetric AES system you increase the key by 2 times (256-512), then the load on the computer will increase by about 2 times.
If you increase the key by 2 times in RCA, then the load will increase by 8 times with a key length of 1024 bits - 2048 bits.
Therefore, in quantum cryptography - it makes no sense.
Quantum cryptography doesn't rely so much on key complexity, it relies more on quantum entanglement, and the fact that a measurement of one photon disturbs the other photon. Hacking is not possible based on the laws of quantum mechanics as we understand them.
I'm not suggesting that quantum cryptography is the only or best approach, just that work is progressing here and it's not necessarily only post-quantum cryptography that should be discussed. There have been objections to QKD itself, but again work is progressing towards better solutions -
Kak's 3 stage protocol for example (basically a quantum version of double-lock):
https://www.researchgate.net/profile/Partha_Basuchowdhuri/publication/1960902/figure/fig2/AS:279938969161741@1443754059593/Kaks-three-stage-protocol.png------------------
Quantum cryptography and quantum internet are photonic systems.
There are no quants there, there are quantum states of photons, such as the spin of a photon.
This is a game of words - "quantum Internet" or "quantum cryptography" - which greatly confuses its understanding by amateurs.
Let's see the essence, photonic systems are a lowering of hands before the call that quantum computers of modern public key cryptography have put.
It's like you used to have an elegant key to your house door, and now you've knocked down your door with a giant stone, counting on the thief not moving it.
That's a step back. Mankind loves these steps because they are man-made, because they create new value in the mass of new equipment, because the Internet can be made both safe and expensive.
Of course, it's the way of the monkey.
This is the path that mankind will leave behind like an old lamp TV when there is a new safe cryptography.
I support the idea that the mind always conquers power.
See if you want to make God laugh, tell him your plans...
In other words, they're systems that transmit light waves:
1) or via fiber optic cable (second half of the 20th century, soon this technology will turn 100 years old), without the possibility of wi-fi points at the end of this path;
2) or transmitting light photons by laser within line of sight.
The example you're looking at: "Micius has demonstrated QKD wirelessly via satellite" is very unhelpful for us ordinary users, but very much liked by rich and government organizations - there's plenty to write off "our" money. The monkey's way, but the rich monkey's way.
In this case, there is a problem, the receiver and the transmitter must be constantly on the same line! And that with a moving satellite!
They must be oriented strictly parallel to each other, which is very difficult to do when the source (satellite) moves at high speed on a circular trajectory.
Such an accurate mutual orientation of the quantum receiver and transmitter is similar to getting a coin from an airplane flying at an altitude of 100 thousand meters - exactly in the slot of the piggy bank, which, moreover, rotates.
It wasn't my idea," says Wang Jianyu, QUESS Project Manager.
These and other achievements, not only are very expensive, they are absolutely unacceptable for us who own devices connected to wi-fi.
This is not the side of progress that the future holds.
Especially since all these experiments have been carried out successfully a long time ago, many of them, not later than 1987.
But in those distant times, people still knew how to think, and this technology was postponed, it was waiting for a more appropriate time, our time.
That's your idea:
"So in quantum cryptography, it doesn't make sense.
Quantum cryptography doesn't rely so much on the complexity of the key, it relies more on the quantum complexity and the fact that measuring one photon interferes with another photon. "
- Cryptography is necessary because stealing information from this channel is not prohibited, it is just a fact that participants will know about it. In other words, this quantum (photon) cryptography does not protect the information, but on the contrary highlights it so that it can be seen with the naked eye, literally. Photons we see...
Your idea:
"There were objections to QKD itself, but again the work is moving towards better solutions, like the three-step Kaka protocol (mainly the quantum version of the double lock):"
- is a logical use of photon states, again with all the resulting disadvantages for us ordinary users to use photons, fiber, direct line of sight and so on, but not wi-fi or 3,4,5,6G is not the way for us.
Our way is keyless cryptography and password-free authentication, my topic is here:
https://bitcointalksearch.org/topic/keyless-encryption-and-passwordless-authentication-5204368.