Abstract: Recently,a growing number of mobile devices use pattern lock as the identity authentication mechanism.To unlock a smartphone,a user must draw a memorized graphical pattern with a finger on the touchscreen where the finger actually leaves its oily residues,also called smudges.The smudges can be exploited by adversaries to reproduce the secret pattern,so that the user’s privacy is always revealed.Based on the research of the existing patten lock,we presented BlindLock as our main result.BlindLock can not only unlock in a pocket,but also use the cover principle to resist smudge attacks and use theory of visual occlusion to resist shoulder surfing attacks.Our user study also shows that BlindLock can significantly improve security,usability and password space of the pattern lock system while incurring minimal cost increase in terms of unlocking time and keeping the original graphics memory.

Key words: Pattern lock,Smartphone,Smudge attack,Shoulder-surfing attack,Authentication