I have a hash of a file $H_1$ and then I add salt and rehash it: $H_2$. I make my $H_2$ and salt public and I use my $H_1$ as a password. How long would it take for this to be cracked with someone trying to figure out all the combinations of the 128 characters and adding the salt to get $H_2$?
So they are trying to figure out $H_1$ and adding salt to confirm that it matches $H_2$. As $Hash(H_1 \| salt) = H_2$, how long would it take to crack the 128 characters to find the $H_1$ that corresponds with this combination?
Please assume SHA3-512 as hash function.