TAPI: Touch-Screen Authentication Using Partitioned Images

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This paper describes and evaluates an alternative approach to a Personal Identification Number (PIN) for small touch-screen devices named TAPI. TAPI replaces a 4-digit sequence with a sequence of 4 partitions of a selection of 16 images, increasing the possible combination of authentication sequences from 105 to over 107 but decreasing the screen space allocated to each possible selection. Across two user studies of TAPI in which 30 participants were randomly assigned authentication sequences, 90% of participants were able to both remember and enter their authentication sequence after one week of non-use.