But that re-keying attack seems like an easily fixed design flaw. The keys are already separate from the hardware, so a "clean" hardware replacement should include a transfer of key material from the old hardware to the new hardware so that re-keying queued messages is not necessary. Of course, now there's the vulnerability of exposing key material during the transfer, but that could be done requiring physical access, eg. a USB OTG cable, or Bluetooth pairing. No need to store the key material in The Cloud. !crypto