Evaluating the Influence of Targets and Hand Postures on Touch-based Behavioural Biometrics.

Users' individual differences in their mobile touch behaviour can help to continuously verify identity and protect personal data. However, little is known about the influence of GUI elements and hand postures on such touch biometrics. Thus, we present a metric to measure the amount of user-revealing information that can be extracted from touch targeting interactions and apply it in eight targeting tasks with over 150,000 touches from 24 users in two sessions. We compare touch-to-target offset patterns for four target types and two hand postures. Our analyses reveal that small, compactly shaped targets near screen edges yield the most descriptive touch targeting patterns. Moreover, our results show that thumb touches are more individual than index finger ones. We conclude that touch-based user identification systems should analyse GUI layouts and infer hand postures. We also describe a framework to estimate the usefulness of GUIs for touch biometrics.