A Preliminary Experiment on Grid Densities for Visual Password Formats

Visual passwords are passwords made by selecting a sequence of objects on a screen, such as symbols, pictures, or patterns, either by manual input or eye-gaze-based input. Visual passwords can be useful alternatives to alphanumeric passwords, particularly for authentication on devices in semi-private or public spaces (e.g., on ATMs, laptops, smartphones, or car dashboards). The grid is an essential factor in the use of a visual password, because it can act as a guide for the position of an object and its identification. In this study, we obtained user judgments of 16 different grid densities for three visual password formats. The grid densities were in between 2×2 to 7×7 cells (columns × rows). The participants were asked to judge how easy to use and how safe they thought the grid densities would be, if they would use it for password authentication with eye tracking in a public setting. The results showed that for each visual password format some grid densities were thought to be relatively difficult to use (e.g., a 7×7 grid) or potentially unsafe (e.g., a 2×2 grid). Following this, the password registration time was measured for 16 grid densities (from 3×3 to 6×6 cells). The participants were asked to memorize and register a visual password (short or long) using actual eye tracking. The preliminary results show that password registration time increased when the number of grid cells increased and that the password format might influence registration as well.