Automated teller machines (ATMs), self-service payment terminals, and other devices that use PIN passwords for user authentication are susceptible to various forms of tampering or attacks in unattended settings. One such attack is shoulder surfing, where an attacker observes the sequence of key presses or steals the password through the use of cameras or peeping methods. To address this issue, this study proposes a design of a pressure sensing matrix combined with a PIN pad that can detect the amount of force applied during key presses, while providing real-time tactile roughness feedback.
Using the high elasticity properties of polydimethylsiloxane (PDMS), the device prototype was designed by defining the required force intervals for key presses and assembling the upper electrode elastic layer, spacer, and lower electrode PCB board.
The input accuracy using the tactile feedback method reached 70.83%, which was significantly higher than the 56.00% accuracy achieved without providing tactile feedback. Moreover, in the case of shoulder surfing, the defense rate of numeric passwords was only 8%, while the defense rate for pressure passwords was 40%, proving effective in protecting passwords.
