Personal authentication is an essential process in various network applications such as online shopping, mobile banking, e-government services, etc. The authentication processes normally use personal or device information which include user password, IP address, device number, MAC address, and bio information such as fingerprints or iris scan. In addition to the direct personal or device information, environmental information can be used for authentication. For example, the location and time of the device use may be considered as important factors to evaluate the risk of false use. The authentication technique is getting more important as the volume of online business and the chances of non-face-to-face contacts enormously increase. This paper proposes a personal authentication technique using sensible sound of keyboard input device. We can extract the unique features of the keyboard stroke sound, and use the features for personal authentication and also for risk evaluation to protect from fraud.