Authentication codes associated with an entity are generated. A stored secret associated with an entity is retrieved. At a first point in time, a first dynamic value associated with a first time interval is determined. A first authentication code based on the first dynamic value is determined. At a second point in time, a second dynamic value associated with a second time interval is determined. A second authentication code based on the second dynamic value is determined. The first and second authentication codes are derived from the stored secret and the amount of time between the first and second points in time is different from the length of the first time interval.