[Gnuk-users] Hardware PIN pad

[Ineiev]

On Wed, Feb 01, 2017 at 09:58:48AM +0100, NdK wrote:
> Il 31/01/2017 09:25, Ineiev ha scritto:
> 
> >>> I've just layed out a draft [0]; the device doesn't fit on the top
> >>> of FST-01, but I think it could be connected to it with a cable.
> >> Why a micro? It could easily be hijacked by an attacker to store the PIN
> >> code.
> > FST-01 already includes a micro, doesn't it?
> Yep. But if it gets tampered, key material is (or should be) lost (IIRC
> updating the fw deletes the keys -- but I could be wrong).

Or any further modifications are disabled.

When the MCU on the pinpad gets tampered, its authentification code
is lost; if the pinpad can't authentificate, FST-01 powers it down.

> >> An MCP23017 (16 IOs) or MCP23008 (8 IOs)
> > A micro-based design would be more straightforward programmatically,
> > and in theory more flexible (e.g. implementing an encrypted
> > connection to FST-01).
> I don't think it's more straightforward, since you have to modify both
> the fw on the ARM and the one on the secondary micro.

Agreed, they are comparable.

> Using an IO expander you don't have to maintain and defend the second
> fw. And nowhere to hide a keylogger :)

What if the attackers replace the IO expander with a micro?

> >> paired with an optional .96"
> >> 128x64 I2C OLED display could probably be better.
> > 128x64 I2C OLED displays are less readily available; I guess they
> > would be considerably less cheap.
> About $2.5 on AliExpress for single pieces.

(0) Does AliExpress sell to anonymous customers?

(1) I wouldn't bet AliExpress will be available for residents
of my country within a year or even 6 months. in my local stores,
such things cost $12 or more (2-digit indicators may be cheaper
than $1).

> And you would "recycle" the same I2C bus used for communication with the
> keyboard controller.

I2C signals are fast-switching. when passed through a cable, they may
emit compromizing levels of radiation.
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