  This work enhances traditional authentication systems based on Personal
Identification Numbers (PIN) and One-Time Passwords (OTP) through the
incorporation of biometric information as a second level of user
authentication. In our proposed approach, users draw each digit of the password
on the touchscreen of the device instead of typing them as usual. A complete
analysis of our proposed biometric system is carried out regarding the
discriminative power of each handwritten digit and the robustness when
increasing the length of the password and the number of enrolment samples. The
new e-BioDigit database, which comprises on-line handwritten digits from 0 to
9, has been acquired using the finger as input on a mobile device. This
database is used in the experiments reported in this work and it is available
together with benchmark results in GitHub. Finally, we discuss specific details
for the deployment of our proposed approach on current PIN and OTP systems,
achieving results with Equal Error Rates (EERs) ca. 4.0% when the attacker
knows the password. These results encourage the deployment of our proposed
approach in comparison to traditional PIN and OTP systems where the attack
would have 100% success rate under the same impostor scenario.
