Google offers one. http://code.google.com/p/google-authenticator/ http://code.google.com/p/google-authenticator/ It implements an open standard for OTP and the

Google offers one. http://code.google.com/p/google-authenticator/ http://code.google.com/p/google-authenticator/ It implements an open standard for OTP and they provide source for a PAM module to require the OTP on the computer side.