The effects of password length and reference profile size on the performance of a multivariate text-dependent typist verification system

The performance of Napier et al.'s typist verification algorithm (Keyboard user verification: toward an accurate, efficient, and ecologically valid al gorithm, International Journal of Human-Computer Studies 43 (1995) 213-222) was assessed in a text-dependent setting. Twenty-nine subjects typed a 17 character password 50 times. False acceptance and false rejection rates wer e then calculated as the number of repetitions of the password included in the reference profile was increased from 6 to 20 and the number of digraphs from the password included in the verification process was increased from 2 to 16. The performance of the system (12% total error rate) was found to be comparable with the best results reported in other studies using text-de pendent algorithms, and substantially better than that reported in studies using a text-independent paradigm with passwords of this length. The relati onship between password length and reference profile size was found to conf orm to an exponential decay function, which accounted for 92% of the variab ility in verification error rates. (C) 1998 Elsevier Science B.V. All right s reserved.