  Unobservable physiological signals enhance biometric authentication systems.
Photoplethysmography (PPG) signals are convenient owning to its ease of
measurement and are usually well protected against remote adversaries in
authentication. Any leaked PPG signals help adversaries compromise the
biometric authentication systems, and the advent of remote PPG (rPPG) enables
adversaries to acquire PPG signals through restoration. While potentially
dangerous, rPPG-based attacks are overlooked because existing methods require
the victim's PPG signals. This paper proposes a novel spoofing attack approach
that uses the waveforms of rPPG signals extracted from video clips to fool the
PPG-based biometric authentication. We develop a new PPG restoration model that
does not require leaked PPG signals for adversarial attacks. Test results on
state-of-art PPG-based biometric authentication show that the signals recovered
through rPPG pose a severe threat to PPG-based biometric authentication.
