The Universal Serial Bus (USB) has become the most popular interface standard for hardware connection, and there has been a huge growth in the number of USB peripheral devices. External USB storage devices, in particular, are the most popular applications in market. Unfortunately, because USB affords high speed data transmission and is extremely convenient to use, many companies have prohibited the use of USB devices to prevent confidential data theft from computer systems via USB ports. However, this compromises the convenience of the USB connection. Therefore, finding a way to take in to account both the convenience of user and secure environment in company has become a significant issue.