A comparison of perceived and real shoulder-surfing risks between alphanumeric and graphical passwords

Previous research has found graphical passwords to be more memorable than non-dictionary or “strong” alphanumeric passwords. Participants in a prior study expressed concerns that this increase in memorability could also lead to an increased susceptibility of graphical passwords to shoulder-surfing. This appears to be yet another example of the classic trade-off between usability and security for authentication systems. This paper explores whether graphical passwords’ increased memorability necessarily leads to risks of shoulder-surfing. To date, there are no studies examining the vulnerability of graphical versus alphanumeric passwords to shoulder-surfing. This paper examines the real and perceived vulnerability to shoulder-surfing of two configurations of a graphical password, Passfaces™(30), compared to non-dictionary and dictionary passwords. A laboratory experiment with 20 participants asked them to try to shoulder surf the two configurations of Passfaces™ (mouse versus keyboard data entry) and strong and weak passwords. Data gathered included the vulnerability of the four authentication system configurations to shoulder-surfing and study participants’ perceptions concerning the same vulnerability. An analysis of these data compared the relative vulnerability of each of the four configurations to shoulder- surfing and also compared study participants’ real and perceived success in shoulder-surfing each of the configurations. Further analysis examined the relationship between study participants’ real and perceived success in shoulder-surfing and determined whether there were significant differences in the vulnerability of the four authentication configurations to shoulder-surfing. Findings indicate that configuring data entry for Passfaces™ through a keyboard is the most effective deterrent to shoulder- surfing in a laboratory setting and the participants’ perceptions were consistent with that result. While study participants believed that Passfaces™ with mouse data entry would be most vulnerable to shoulder-surfing attacks, the empirical results found that strong passwords were actually more vulnerable.