“…However, due to the simplicity and easy guessability of the PIN and pattern passcodes [ 12 ] (e.g., shoulder surfing attack [ 13 ] and smudge attack [ 8 ]), and the risk of fingerprint loss from public events (e.g., attackers can get fingerprints from public events with the help of a standard camera [ 9 ]), a growing number of biometric features ( i.e. , signature or gesture based methods [ 14 , 15 ], touch dynamics [ 16 , 17 ], and keystroke dynamics [ 18 , 19 ]) has been applied to strengthen smartphone authentication [ 14 , 15 , 16 , 17 , 18 , 19 ].…”