[wcoenen]

128 bits of entropy should suffice to make brute forcing impossible.

That corresponds to a 22 character mixed-case alphanumeric password. (62 choices per character, 62^22 > 2^128). But only if the characters are chosen randomly by a password generator; characters chosen by a human will have patterns and therefore lower entropy.

80 bits of entropy should still be enough to occupy a large amount of specialized hardware for a long time. That would correspond to 14 characters.