[maginx]

The size/computational complexity of usage also only grows as a polynomial with RSA. But even with this in mind, a quantum computer that can crack in polynomial time is still problematic. While you can increase the key size, the operator of the quantum computer could enlarge his computer, a true cat-and-mouse game. Unlike the current situation where usage complexity grows as a polynomial, while cracking grows exponentially. This difference is the reason why we can pick key sizes where signing/decryption takes a millisecond while cracking it takes (presumably) billions of years.