Back-of-device authentication on smartphones

TLDR

This paper introduces BoD Shapes, a back‑of‑device authentication method for smartphones. The authors evaluated BoD Shapes in a 24‑participant user study, comparing it to PIN, Android grid unlock, and a front‑side version to assess performance and security. BoD Shapes proved significantly more secure than the other methods while achieving rapid entry (up to 1.5 s) and showing speed gains with practice.

Abstract

This paper presents BoD Shapes, a novel authentication method for smartphones that uses the back of the device for input. We argue that this increases the resistance to shoulder surfing while remaining reasonably fast and easy-to-use. We performed a user study (n=24) comparing BoD Shapes to PIN authentication, Android grid unlock, and a front version of our system. Testing a front version allowed us to directly compare performance and security measures between front and back authentication. Our results show that BoD Shapes is significantly more secure than the three other approaches. While performance declined, our results show that BoD Shapes can be very fast (up to 1.5 seconds in the user study) and that learning effects have an influence on its performance. This indicates that speed improvements can be expected in long-term use.