project idea: portable password safe

Mark Tuson markfptuson at gmail.com
Fri Sep 13 06:52:22 EDT 2013


Is this a Nanonote project, or is it more dreaming of hardware that'll 
never exist?


On 13/09/2013 10:14, Werner Almesberger wrote:
> Felix wrote:
>> That's a new business idea, a camera module with built-in QR reader
>> firmware, with UART output; could be interesting for some integrators. Oh,
>> wait!! That already exists!![1]
> Looks expensive, though.
>
>> You can always opt to hash some data (e.g. the url) and get something
>> shorter.
> Yes, and it doesn't even have to be globally unique. If you have,
> say, 1000 accounts, 20 bits would be enough for only one collision
> (on average). With 48 bits, you'd then be collision-free with a
> probability of 99.998%
>
> Plus 8 bits for CRC, three for lead-in, and five for the message
> type (0 = service hash, 1 = account hash, the rest reserved), we're
> at only 64 bits. Not too bad.
>
> Actually, best to double the last bit of each non-lead-in byte and
> grow the lead-in to 9 bits. That way, the code can be sent
> continuously and the device can automatically synchronize.
>
> That would then be 64 + 7 + 6 = 77 bits.
>
>> Also in my jsfiddle I've put 100ms between bits, but you can try
>> to lower it to 33ms (most of monitors works on 60hz, so it should work).
> You probably also get some jitter from the browser and background
> system activity. And then everything gets modulated by the refresh
> rate. So you'd probably want at least 3 refresh cycles per bit.
>
> Next: a suitable sensor. The one in [1] doesn't seems to be very
> effective. Alas, there's no part number one could use to get the
> characteristics.
>
> - Werner
>
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