[Cryptography] You can't trust any of your hardware

[Nemo]

"Joe St Sauver" <joe at oregon.uoregon.edu> writes:

> The best practical solution I can think of to fix this would be to
> interpose a manually operated physical switch on each device that
> would need to be intentionally closed by the user to update the
> firmware on the device.

Yes, that is one idea on the right track. Another is to have the device
only accept firmware updates with an appropriate cryptographic
signature.

The iPhone uses both of these approaches.

http://theiphonewiki.com/wiki/DFU_Mode

"
    Plug your device into your computer with a USB cable.
    Turn off the device.
    Hold the Power button for 3 seconds.
    Hold the Home and Power buttons for 10 seconds.
    Release the Power button but keep holding the Home button.
    After about 15 seconds you will be alerted by iTunes saying that it
    has detected a device in Recovery Mode.
"

Granted, firmware signature schemes do have this funny tendency to get
(jail)broken.

Still, unless it was designed by idiots, any firmware update procedure
obviously must require the user to diddle with the physical controls in
some way. Regrettably few devices meet the precondition.

Jerry Leichter <leichter at lrw.com> writes:

> How many USB devices have ever been patched after sale?

I dunno... How many iPhones are there?

I own one of these:

http://worldwide.bose.com/productsupport/en_us/web/bluetooth_headset_series2/page.html
"Software updates are available"

Does my USB printer count as a "USB device"?

I am fairly certain updatable USB devices are the norm, not the
exception.

 - Nemo
   https://self-evident.org/