Quote from: Speakeron on December 12, 2013, 10:16:38 AM

Quote from: kjj on December 10, 2013, 05:45:53 AM

Quote from: jdbtracker on December 10, 2013, 05:14:29 AM

so... if we aimed all the Hashing power of the Bitcoin network on one address it would take 500 million years? Hey man It's only a matter of time before insane quantum computers just start cracking the codes by the second. I can imagine this will happen one day, when the Bitcoin network migrates to a new protocol based on quantum security. Those computers will tear Bitcoin apart when they finally are able to produce them in mass, and start migrating all the accounts to a new system like a block reward, Or just like the free market migrate by choice to something safer.

Quantum computers do not appear to be particularly adept at hashing.

More specifically, using Grover's Algorithm, the time taken to find a preimage of a hash (i.e. a reverse hash) is the square-root of the time for a classical attack. e.g. a 256-bit hash becomes like a 128-bit hash. It's not considered a big problem since the times are still very long.

Not to wander too far off topic, but Grover's solves circuits. Circuit means the function must be completely unrolled in both time and space, so that there is no memory and no iteration, just logic gates. A circuit for SHA-256 is far beyond our capabilities, much less double SHA-256. I'm not sure we are even capable of designing such a thing.

Oh, and did I mention that all those trillions (quadrillions? pentillions? who knows?) of logic gates have to be reversible quantum gates? And that they all have to be kept coherent?