Challenge-Response Authentication Using In-Air Handwriting Style Verification

Challenge-response (CR) is an effective way to authenticate users even if the communication channel is insecure. Traditionally CR authentication relies on one-way hashes and shared secrets to verify the identities of users. Such a method cannot cope with an insider attack, where a user can obtained the secret (i.e., the response) from a legitimate user. To cope with it, we design a biometric-based CR authentication scheme (hereafter MoCRA), which is derived from the motions as a user operates emerging depth-sensorbased input devices, such as a Leap Motion controller. We envision that to authenticate a user, MoCRA randomly chooses a string (e.g., a few words), and the user has to write the string in the air. Using Leap Motion, MoCRA captures the user's writing movements and then extracts his / her handwriting style. After verifying that what the user writes matches what is asked for, MoCRA leverages a Support Vecter Machine (SVM) with co-occurrence matrices to model the handwriting styles and can reliably authenticate users, even if what they write is completely different every time. Evaluated on data from 24 subjects over 7 months, MoCRA managed to verify a user with an average of 1.18% (Equal Error Rate) EER and to reject impostors with 2.45% EER.