“…However, it also raises concerns about the potential risk of sensitive user information being leaked. These methods make use of physical characteristics of the user, such as brain signal [36,46], photoplethysmogram [47], breathing patterns [37,44], ultrasonic-based mapping [45,48] and facial recognition [31,32], as well as movement detection, including head movement [41,42], eye gaze [38,40,43] and ball throwing activities [33][34][35]39], and finally haptic authentication [30]. An interesting approach of John et al [38,40] is the usage of iris defocusing, in an attempt to prevent iris information from being transferred and risk of an attack, at the cost of lower information and authentication success.…”