Abstract or Summary:
Previous work in the literature has shown that back-of-device (BoD) authentication is significantly more secure than standard front-facing approaches. However, the only BoD method available to date (BoD Shapes) is difficult to perform, especially with one hand. In this paper we propose BoD Taps, a novel approach that simplifies BoD authentication while improving its usage. A controlled evaluation with 12 users revealed that BoD Taps and BoD Shapes perform equally good at unlocking the device, but BoD Taps allows users to enter passwords about twice faster than BoD Shapes. Moreover, BoD Taps is perceived as being more usable and less frustrating than BoD Shapes, either using one or two hands.