Very generally, if your string is N bits, a polynomial attack is one that can solve it in O(n^i) bits, where i is some fixed number. A non-polynomial time atta

Very generally, if your string is N bits, a polynomial attack is one that can solve it in O(n^i) bits, where i is some fixed number. A non-polynomial time attacker would be something beyond that, like O(2^n). Technically this treats O(n^2) and O(n^10000) as the same effort.