Mobile device users avoiding observational attacks and coping with situational impairments may employ techniques for eyes-free mobile unlock authentication, where a user enters his/her passcode without looking at the device. This study supplies an initial description of user accu- racy in performing this authentication behavior with PIN and pattern passcodes, with varying lengths and visual characteristics. Additionally, we inquire if tactile-only feedback can provide assistive spatialization, finding that orientation cues prior to unlocking do not help. Measure- ments of edit distance and dynamic time warping accuracy were collected, using a within-group, randomized study of 26 participants. 1,021 passcode entry gestures were collected and classified, identifying six user strategies for using the pre-entry tactile feedback, and ten codes for types of events and errors that occurred during entry. We found that users who focused on orienting themselves to position the first digit of the passcode using the tactile feedback performed better in the task. These results could be applied to better define eyes-free behavior in further research, and to design better and more secure methods for eyes-free authentication.
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