project idea: portable password safe

Werner Almesberger werner at
Sun Sep 8 12:44:28 EDT 2013

EdorFaus wrote:
> I don't think they have to be, considering one of the products I've
> seen that uses DASH7 is the HayTag

Ah, nice ! There, the long range is also put to good use.

> Heh. Well, it actually makes sense to do it this way, since it's a good
> representation of what a keyboard really is and does - and sometimes,
> you don't really care which letter is printed on it, as long as you can
> recognize the key; or you might have a need to remap it *anyway*.

Yeah, but they could have added a little table with a keycode to
glyphs mapping. It's not as if the USB protocols would skimp on
bureaucracy elsewhere ...

> Actually, now that I think about it, I think we're going to need to
> be able
> to tell the user that a password can't be typed with the currently
> selected
> layout,

Hmm yes, that could happen. There's the Alt+Number trick but I'm
not sure this works everywhere.

> Hm, there's an idea - I assume the device will be able to recognize
> which
> dongle it's in the vicinity of (since they're paired with keys
> etc.), so
> maybe we could have a way to autoselect the layout to use based on
> that?

Sure, the entry could include a default layout as well. We could
also check bCountryCode to see if there's a useful hint there,
and set our own bCountryCode, in case the OS knows how to use it.

> ... Hm, what should happen if the device is in the vicinity of more
> than
> one known (and paired) dongle?

It could list them by signal strength and you'd have to select
which one you want to talk to. Or maybe just make the strongest
the default and let the user override it.

> Oh well, most of that is just software, so we can deal with those
> features
> when we have something that works for the basic use case.

Yeah, all that should be easy :)

> That's a good point. With a device like this, and a basic RTOS, it's
> probably going to be just as fast to boot each time as it would be to
> suspend/resume with something more complex (like Linux),

The standby current of modern MCUs is usually negligible in this
kind of scenario. An electromechanical power switch could be a
nice extra security feature, though.

> Hm, I wonder - would it be feasible to have the device side USB plug
> be a
> male A plug on a cord that retracts into the device body?

I'd stay away from fancy mechanics. The more moving parts, the more
things break ;-)

- Werner

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