This paper proposes an effective countermeasure to an intrinsic hardware vulnerability of the keyboard controller that causes sniffing problem on the password authentication system based on the keyboard input string. Through the vulnerability, some possible attacker is able to snoop whole the password string input from the keyboard even when any of the existing keyboard protection software is running. However, it will be impossible for attackers to gather the exact password strings if the proposed policy is applied to the authentication system though they can sniff the keyboard hardware protocol. It is expected that people can use secure Internet commerce after implementing and applying the proposed policy to the real environment.