P²Auth: Two-Factor Authentication Leveraging PIN and Keystroke-Induced PPG Measurements

Personal Identification Number (PIN), as one of the primary means of protecting digital properties and privacy on mobile devices, has been suffering from shoulder surfing attacks and weak password guessing for the long term. Recent years witness the growing interest in two-factor authentication that takes advantage of two different ways for mutual verification, thereby strengthening user authentication's accuracy and reliability. Especially with the popularity of smartwatches, more physiological signals are readily available to facilitate two-factor authentication. This paper presents a lightweight and unobtrusive two-factor authentication scheme, P ² Auth, integrating the PIN and unique keystroke-related Photoplethysmography (PPG) measurement on wearables. Specifically, we propose the transformation of the multivariate PPG signal induced by the keystrokes to extract reliable biometric features. We develop short-time energy-based methods to identify the input cases, thus enabling support the authentication for both one-handed and two-handed input cases. Furthermore, we also consider the situation where there is no fixed PIN and design a new enhanced privacy scheme by combining the PPG measurements of different keystrokes to improve authentication security. The experiments involving 15 volunteers demonstrate that our prototype system can achieve an average authentication accuracy of over 95% for one-handed cases and over 90% for two-handed cases.