Development of keypads which use colors or shapes to prevent shoulder surfing

In conventional smart phones and ATMs, a four-digit passcode is entered into a keypad, and the user confirms whether the passcode matches the keypad. However, there is a risk that a third party can easily steal the password by watching the code entry or analyzing the position of fingerprints left on the keypad. There are other solutions, such as biometric authentication or the use of special displays, but both of them are costly and difficult to implement. In this study, we propose a keypad that does not leave fingerprints on the screen, is low cost, and can be used to input passcodes without worry, even if someone is standing next to it. The proposed keypad uses cursors that are moved by directional keys to select numbers, making fingerprint analysis difficult. Because attackers do not know the color that the user has selected, they cannot know which cursor the user is moving. To verify the safety and convenience of this system, we conducted experiments on subjects in their 20 s and 50 s. The results showed that the average difference in authentication time from the conventional method was about 5 s, and the method was generally convenient. We conclude that our keypad system is secure, because no peeping attacks on a subject were successful in guessing the subject’s passcode.