Use a usbpen as hardware key for access to pc

Hi,

I would know if is possible to use a usbpen for close a pc to unautorized user. I would say that if that usbpen isn't plug at boot the pc won't boot.

I think that i would use vendor/device id and a key in a file on the pen or a gnupg img something like this.

Someone have a project or a howto to send to me...

Thanks