To introduce quantum networks into the marketplace, engineers must overcome the fragility of entangled states in a fiber cable and ensure the efficiency of signal delivery. Now, scientists at Qunnect Inc. in Brooklyn, New York, have taken a large step forward by operating just such a network under the streets of New York City.
      •  Sekoia   ( @Sekoia@lemmy.blahaj.zone ) English
        1•26 days ago

        You can have post-quantum cryptography using classical computation, though

        (“Simply” pick a problem with no quantum acceleration. I think Elliptic Curves Cryptography works, but I’m not an expert)

        •  YtA4QCam2A9j7EfTgHrH   ( @YtA4QCam2A9j7EfTgHrH@infosec.pub ) English
          3•26 days ago

          Quantum crypto is different than cracking encryption with a quantum computer. The point of quantum crypto is that the key exchange is perfectly secret. If it is observed, the people exchanging keys will know due to entanglement bs that I’m too dumb to understand.

          But you basically get the perfect uncrackable encryption of one time pads without having to manage one time pads.

          •  Sekoia   ( @Sekoia@lemmy.blahaj.zone ) English
            3•26 days ago

            Oh yeah, that. My bad, mixed 'em up.

            The original algorithm doesn’t use entanglement, though! Just the fact that measurements can change the state. You can pick an axis to measure a quantum state in. If you pick two axes that are diagonal to each other, measuring a state in the “wrong” axis can give a random result (the first time), whereas the “right” one always gives the original data.

            So the trick is to have the sender encode their bits into a randomly-picked axis per bit (the quantum states), send the states over, and then the receiver decodes them along a random axis as well. On average, half the axes will match up and those bits will correspond. The other bits are junk (random). They then tell each other the random axes they picked, which identifies the right bits!

            They can compare a certain amount of their “correct” bits: if there’s an eavesdropper, they must have measured in the wrong state half the time (on average). Measurement changes the state into its own axis, so the receiver gets a random bit instead of the right one half the time. 25% of the time, the bits mismatch, when they should always correspond.