BoD Shapes is a novel authentication method for smartphones that uses the back of the device for input. We argue that this increases the resistance to shoul- der 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 ver- sion of our system. Testing a front version allowed us to di- rectly compare performance and security measures between front and back authentication. Our results show that BoD Shapes is significantly more secure than the three other ap- proaches. 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 per- formance. This indicates that speed improvements can be ex- pected in long-term use.

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De Luca, A., von Zezschwitz, E., Huong Nguyen, N. D., Maurer, M., Rubegni, E., Scipioni, M. P., Langheinrich, M., Back-of-Device Authentication on Smartphones, Submitted at CHI2013 – Nominee for the Best paper award (forthcoming, 10 pp.)