The value of posture, build and dynamics in gesture-based user authentication

User authentication based on biometrics such as fingerprint, iris, face, speech or gait has been around for many years. Recently, intentional user gestures have been shown to be a promising modality for user authentication. However, it is unclear how much of the performance can be attributed to pure biometric information that a user has no control over, such as individual limb lengths, and how much to the gesture dynamics, that a user can fully control. A related question is: How easy is it to copy these dynamics? In this paper, we propose a framework to decompose a gesture into three components: initial posture, limb proportions, and gesture dynamics. We then study the impact of each component and various component combinations on the performance of gesture-based user authentication using a dataset of 36 users performing 3 gestures of varying complexity. We also study spoof attacks using the same dataset and show, somewhat surprisingly, that amateurs are unable to copy gestures with sufficient accuracy so as to significantly degrade the overall authentication performance even when they are trained on users that they are closest to. While training certainly improves an attacker´s ability to copy gesture dynamics, it seems that the unique limb proportions (which cannot be altered) and the initial posture (which amateurs attackers fail to pay attention to), more than make up for the loss due to compromised dynamics (which can always be renewed).