Seems like guessing a password would be an example. Assuming that the length of a password is N, if the machine can somehow guess the password, it can verify i

Seems like guessing a password would be an example. Assuming that the length of a password is N, if the machine can somehow guess the password, it can verify in O[N]. On the other hand, if the password is not known, the number of possible combinations to try would be exponential.