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Advances in mathematics/computing will make these calculations feasible after decades at most.
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What calculations? Brute force? No, you are mistaken. Brute force of 256 bit will not be feasible.

with quantum computing in the distant future there is no reason to say it could not happen

with quantum computing in the distant future there is no reason to say travels into the past could not happen

time travel is potentially possible according to what we know... i dont get it

time travel to the past is impossible. to the future it is theoretically possible when you move fast enough.