Evaluation on a keystroke authentication system by keying force incorporated with temporal characteristics of keystroke dynamics

This paper presents the study to develop and evaluate techniques to authenticate valid users, using the keystroke dynamics of a user's PIN number entry on a numerical keypad, with force sensing resistors. Added with two conventional parameter lists of elements, i.e. digraph latency times and key hold times, keying force was chosen as a third element. Two experiments were conducted. The first experiment was to evaluate whether the three types of elements derived from keystrokes have a significant effect for subjects and to examine how trials and session effects generated the variation of the three elements. The second experiment was to demonstrate the system performance by calculating the False Rejection Rate (FRR) and the False Acceptance Rate (FAR) of the system. In the second experiment, a total of 20 keystrokes were recorded from each subject one week after the memorizing session, in order to evaluate the FRR of the system. To evaluate the FAR of the system, the subjects pretended to be impostors, and therefore they repeatedly watched videotaped pass trials made by a valid user as many times as they desired, and tried to imitate the keystroke dynamics of the valid users. The subject's keystrokes were then evaluated on whether they could fool the system. The first experiment, ANOVA revealed that a significant effect of subject was found on each of all three elements. Trial was not significantly affected to digraph latency times and peak force; however, it was significantly affected to key hold times. There was a trend that keystroke dynamics characterized by each element showed reformation of their patterns and reached a steady state over the 10 weeks of experimental sessions. The results of the second experiment showed the average equal error rate to be 2.4%. The results of system performance were compared with those of other studies and concluded that it was difficult to obtain enough information to behave as a perfect impostor by monitoring the videotaped keystrokes.