14. An electronic device comprising: a detection unit configured to detect a request for an authentication function; a display unit configured to display a first string comprising at least one user-defined number or character in a storage unit and at least one randomly selected number or character in response to detecting the request for the authentication function; a receiver configured to receive a second string including at least one user-input number or character via a touch screen; and a control unit configured to: determine whether the at least one user-input number or character in the received second string is in a predefined one to one correspondence with the at least one user-defined number or character in the displayed first string, and determine a user authentication in response to determining that the at least one user-input number or character in the received second string is in the predefined one to one correspondence with the at least one user-defined number or character in the displayed first string, wherein the user authentication is determined regardless of the others except at least one user-input number or character in the predefined one to one correspondence with the at least one user-defined number or character in the displayed first string.
14. An electronic device comprising: a detection unit configured to detect a request for an authentication function; a display unit configured to display a first string comprising at least one user-defined number or character in a storage unit and at least one randomly selected number or character in response to detecting the request for the authentication function; a receiver configured to receive a second string including at least one user-input number or character via a touch screen; and a control unit configured to: determine whether the at least one user-input number or character in the received second string is in a predefined one to one correspondence with the at least one user-defined number or character in the displayed first string, and determine a user authentication in response to determining that the at least one user-input number or character in the received second string is in the predefined one to one correspondence with the at least one user-defined number or character in the displayed first string, wherein the user authentication is determined regardless of the others except at least one user-input number or character in the predefined one to one correspondence with the at least one user-defined number or character in the displayed first string. 15. The device of claim 14 , wherein the first string comprises a random mix of the at least one user-defined character and the at least one randomly selected number or character.