An apparatus for authenticating a user to gain access or entry. A correct final time interval count is associated with execution of a secure system act; it is revealed to or known by the user prior to ending the secure system act. A counter determines a final time interval count representing a number of time intervals from the beginning to the end of the secure system act. A validation unit validates the user as a valid user if the secure system act matches a correct secure system act and the final time interval count matches a correct final time interval count. If both determinations are affirmative the validation unit produces an authentication signal. In turn a control unit generates a control signal that permits access or entry to the user.