Virtual Step PIN Pad: Towards Foot-input Authentication Using Geophones

The use of personal identification numbers (PINs) for authentication is ubiquitous due to their simplicity and flexibility. In this work, we present virtual step PIN pad, a novel and practical PIN entry scheme that allows a user to enter a PIN through foot tapping on the ground. The virtual step PIN pad utilizes geophones to collect structural vibration signals caused by foot tapping. When a user generates the activation signals by performing a predetermined sequence of foot taps within the target area, the virtual step PIN pad will be launched, and takes the foot tapping input by the user. The system then demodulates the corresponding structural vibration signals into a PIN. We have developed a prototype of the virtual step PIN pad and conduct a suite of experiments to evaluate its practicality and security. Experimental results show that the virtual step PIN pad can achieve an average success rate of 96.5% for inputting a human-chosen 4-digit PIN. Meanwhile, the success rate for an adversary at a distance of more than 2.5 meters away from the PIN pad to infer the target PIN decreases to below 3%.