Identification of Pressed Keys From Mechanical Vibrations

This paper describes an attack that identifies the sequence of keystrokes analyzing mechanical vibrations generated by the act of pressing keys. We use accelerometers as vibration sensors. The apparatus necessary for this attack is inexpensive and can be unobtrusively embedded within the target equipment. We tested the proposed attack on an ATM keypad and a PIN-pad. We achieved the key recognition rates of 98.4% in ATM keypad, 76.7% in PIN-pad resting on a hard surface, and 82.1% in PIN-pad hold in hand.