"Just as it took decades for us to get supercomputers in our pockets, it will take decades to work through all the engineering problems necessary to build large-enough quantum computers."<p>This is not an accurate analogy, and you shouldn't believe that there is a continuous engineering path to practical quantum computing as there was for miniaturization of semiconductors. We understood that there was "plenty of room at the bottom" for semiconductors and classical computation and had "Moore's Law" which pointed to a future with supercomputers in our pocket. However the physics of quantum computation are not so well bounded today, and the author acknowledges that we may not be able to build such quantum computers, and he is placing a bet.<p>Let me place my bet: error correction will prove intractable for quantum computation, with a recursive relationship between the size and coherence time of a topological qubit, such that the minimum number of particles required to factor N-bit numbers will exceed the number of particles in the universe for an N that is small enough to just keep using RSA on classical computers.
>But if the unimaginable happens, that would leave us with cryptography based solely on information theory: one-time pads and their variants.<p>If I remember correctly Zones of Thought series by Vernor Vinge has aliens that can do that (I don't want to spoil out why, because it's one of the great ideas in the book). As a countermeasure, there are spaceships carrying massive amount of bits around to be used as one-time pads.
> Yes, I know that quantum key distribution is a potential replacement for public-key cryptography. But come on -- does anyone expect a system that requires specialized communications hardware and cables to be useful for anything but niche applications?<p>I don't think there is any inherent reason why this would have to be done using "specialized communications hardware and cables". Didn't the Chinese just demonstrate entanglement sharing via satellite?<p>I could imagine a post-quantum computing era where it is even possible to know, with certainty, if you have been hacked, or data breached, because of quantum cryptography. We are not any where near this kind of technology right now, but the physics is real.
Numerous post-quantum public key cryptosystems exist that a completely classical party can run. Schneier left these out of his discussion for key distribution if quantum supremacy were to ever occur.
Perpetual motion machines. We heard it before. Controlled fusion, free energy, bla bla bla, bullshit, more bullshit, and a bit mor bullshit. Ohh look! The Santa Claus !