[Gnuk-users] Flying Stone Bare Bone 48

[NIIBE Yutaka]

On 01/26/2016 01:47 AM, NdK wrote:
> Urgh... That would allow an attacker to read device keys w/o being
> detected...

Yes.  Let me explain the feature.

It is under control by a user of MCU (from the viewpoint of MCU
manufacturer), although it would not necessarily mean it's under
control by a user of a token.

By making the process (of manufacturing of Gnuk25519 Token)
transparent, I believe that users of Gnuk25519 Token will be
able to make sure it's under control by themselves.


The document is:

    AN4507:
    Using the Kinetis Security and Flash Protection Features
    by: Melissa Hunter, Automotive and Industrial Solutions Group


http://cache.freescale.com/files/microcontrollers/doc/app_note/AN4507.pdf

To quote:

======================
2.1.1.2 Backdoor key enable

The second option in the FSEC register is a backdoor key enable option
controlled by FSEC[KEYEN].  When enabled, the backdoor key option
allows for a means of temporarily disabling flash security if the
correct 64-bit key value is provided when executing a flash verify
backdoor access key command.
======================

Very good, _if_ this means no hidden backdoor.  Well, I don't know if
there is or not, actually.

> Well, As an engineer in a big company you wouldn't have full control of
> the docs given to the clients :(

In Japan and its culture, it is quite uncommon to have an author name
in such a document.  I'd admire the culture having author names in
technical documents.

> PS: instead of a plain white led, why not a WS2812B one? RGB from a
> single pin (optionally more LEDS can be cascaded).

Thanks for your suggestion.  Yes, I considered the option, because it
is common these days (we can find the example in original ST-Link/V2).
I agree that it is cool, convenient and cheap (for > 95% people, I
guess).

Once, I tried to use two/three color LED.  However, I learned that one
of my friends has disability to recognize colors (I think we call it:
red-green color-blindness), and the interface of color LED is very
annoying for him.  While I don't have ability to make FS-BB48
universally good for any people, I do make it less annoying to my
friends.
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