&gt; The only way to move information from the outside world into the laptop&#x2F;HSM is via USB drive. Accordingly, the key-signing request is loaded into the laptop via USB.<p>Hmm, how sure are they that the OS only allows USB drives (as opposed to keyboards, network controllers, etc.), and contains no exploitable bugs?  Is an image of the media the laptop was booted from publicly available, and has it been audited?<p>I almost feel silly asking, given all the time spent designing this and how smart the people are, but after all that trouble it seems amateurish to use USB...