Dissecting pattern unlock: The effect of pattern strength meter on pattern selection

Pattern unlock is one of the entry protection mechanisms in Android system for unlocking the screen. By connecting 4–9 dots in a 3 × 3 grid, the user can set up an unlock pattern which is equivalent to a password or a PIN. As an alternative to the traditional password/PIN, the visual pattern has gained its popularity because of the potential advantages in memorability and convenience of input. However, the limited pattern space and existing attacks such as shoulder surfing, or smudge attack make this mechanism weak in security. In this paper, we analyzed the characteristics of all valid patterns and proposed a way to quantitatively evaluate their strengths. We then designed two types of pattern strength meters as visual indicators of pattern strength. We conducted a user study that involved 81 participants. The results of the user study showed that the presence of visual indicator of pattern strength did encourage users to create visually complex patterns, thus increasing the security of pattern unlock.