Old PC as Hardware Security Module?

[Robert J. Hansen]

> How do they work?

A (very) small display to show the hash that's being signed and an  
integrated PINpad.  PC sends data to the smartcard unit for signing,  
then signals the SC unit "okay, I'm done, sign now, please".  SC  
pauses to display to the user the hash and get the PIN directly on  
its own trusted hardware.  If the PIN is entered, SC does the  
signature and tosses it back to the PC.  If the operation is  
canceled, SC returns some kind of op-cancelled value.