> You can never straight up brute force a full-strength 512-bit key. That's just a fact of the universe.
If there is some number of bits n < 512 where brute forcing an n-bit key is not a "fact of the universe", does it stand that cracking 512 bit keys is also not a fact of the universe?
No? That's like saying "if my glass can fit a drop of water, then it can also fit an ocean". There is an upper bound to how much processing power there can be in the universe, and 512 bit keys need more than that to be cracked.
The key words here are "brute force" -- there might be some [possibly quantum] techniques around it, but probabilities around guessing and checking an arbitrary number remain constant.
