This locking feature is the most widely used by the general public. The pattern locking feature consists of a grid with simple user interface. The user selects the starting point and drags the pattern. However, the number of patterns provided is limited. This feature is vulnerable to smudge attacks by malicious attackers to unlock the pattern.
This locking feature is used by existing feature phones. In the conventional PIN, only four numbers could be entered. Now, a PIN may comprise a minimum of 4 up to 16 numbers. It has a weakness in that if a user sets up numbers that are related to the user (such as a birthday), it will be easier to unlock. Therefore, random numbers and longer PINs make the code stronger. However, the positions of the input numbers are always fixed on the screen so that it is vulnerable to smudge attacks. In addition, it is difficult to memorize the excessively long numbers that are needed for stronger security.
The password is the most widely used locking feature, not only for smartphones but also for logging in for email, home page, and SNS use. This locking feature can include a combination of various numbers, letters, and special characters. However, if the password chosen is the same as one which has been previously used, it may be exposed easily. In addition, password syndrome might occur if different passwords are used in situations where a login is required.
This is a locking feature linked to the user’s face; it employs the smartphone’s built-in camera. To set up the feature, the user’s face is captured in the face recognition boundary to be used for the locking system. To unlock the system, a facial expression similar to the setup face has to be recognized. This locking feature is vulnerable if malicious users provide a similar facial expression or have photos of the legitimate user.
In order to overcome the vulnerability of face recognition, face with voice is used as a locking feature. For its setup for locking, it follows the face recognition method along with a voice recording of the repeated pronunciation of set words. However, problems similar to those related to face recognition exist, where a similar face or photo can be used for facial recognition. Voice recognition can also be unlocked using voice modulation or a recorded voice. Thus, the usage frequency of this method is very low. Furthermore, if face or voice recognition does not work on the first attempt, the user has to attempt to unlock the device multiple times, which is inconvenient.
