[Gnuk-users] Flashing the FST-01 and generating and importing a key in a secure environment

[Jonathan Schleifer]

Am 16.02.2015 um 07:21 schrieb NIIBE Yutaka <gniibe at fsij.org>:

> In the article you wrote:
>> you should not order the FST-01 with the shrink tube, as you cannot
>> access the SWD port there!
> 
> Yes, I recommend having SWD programmer.
> 
> Nevertheless, usually, I recommend to buy the FST-01 with the shrink
> tube.  I also call it the "transparent" FST-01, because the tube is
> transparent.  I made a version in this way among three, since I felt
> it's a kind of manufacturer responsibility to "pack" it (at least for
> a version).
> 
> It is OK for users to order the "transparent" FST-01, when they can
> trust the process of manufacturer of FST-01, or in another condition
> like: it were rather harder for them to trust a SWD programmer.

It's not so much about trust, but about using the SWD port to flash a different firmware :). I added this note as I made the mistake and first ordered one with the heat shrink without realizing that I can't access the SWD port then and someone who read my blog made the same mistake. Luckily, in both cases it was noticed before it was shipped so that the one with the case could be ordered instead.

> Well, in general, it's a matter of degree from my point of view.
> 
> It is not recommended to buy versions of FST-01 other than
> "transparent", if you won't flash by yourselves, because it is rather
> easier for a middle person to modify its flash ROM maliciously.

Flashing the firmware would erase all keys, right? So, you would notice if someone flashes your Gnuk. And for the firmware it comes with, well, the first thing for me was updating it to 1.1.4 anyway :).

> For someone, it is better to build her own version of FST-01 by
> herself, ordering PCB and parts by herself and assembling it by
> herself (or ordering assembling by some hardware company too).
> 
> It would be also good to write your own C compiler to build Gnuk
> safely, if you really care about that.
> 
> When FST-01 will be famous enough, it would be better for another
> person to use STM8S Discovery Kit instead of FST-01:
> 
>    Discussion at DimSumLabs:
>    https://identi.ca/gniibe/comment/88SzKr4USxW-tpwDdAqMqg
> 
> 
> Confession:
> My math capability is quite limited, even with Japanese abacus.  If I
> have enough math skill, I think that I should be able to calculate a
> signature by my own hand calculation.  With lack of the skill, I rely
> on my FST-01.

This all pretty much boils down to "Can we trust hardware?". The answer for that is unfortunately no. There are several papers on how you can manufacture a chip with a backdoor that you can't even spot with an electron microscope. The only way to find out is to the destroy the chip. But even if you destroyed it and it had no backdoor, the next chip might have one. So you can never know.

--
Jonathan