[Cryptech Tech] Noise board on Novena

[Benedikt Stockebrand]

Hi Joachim and list,

> Good to see you back on the list!

I never left:-)

It's just that at least to the end of this month I'll be rather busy
except over the weekends, and the discussions here aren't something I
want to do after a long day at a customer.

> Ah, yes. I was obviously being confusing. Let me back up:
>
> The entropy providers are responsible for connecting any external noise
> (or entropy) source to the TRNG _inside_ the FPGA and provide entropy
> data in a systematic way to the mixer. The interface I described above
> is between the mixer and any entropy provider and adhering to it will be
> easier to integrate. (We can always add a wrapper).

OK, that's very good news.  One of those things still worrying
me is that I make assumptions about the complexity of FPGA based
implementations that may be fine in theory (done some work on that in
theoretical computer science) but blow up in your face if you actually
try to implement them.

> [...]
>
> (On top of that, I really don't like SPI. ;-)

Neither do I, but this isn't as much a matter of liking or not; it's
rather about the fact that SPI uses four different modes you have to
agree on all ends on, makes you deal with nasty timing issues and
behaves rather badly when things break on one end.

In other words, we've got plenty of reasons not to like it:-)

But what are the alternatives? I2C isn't exactly nice either, and I
guess using a UART interface with an FPGA isn't exactly trivial either.

> Yes. This is _exactly_ how the avalanche noise entropy provider in the
> TRNG works today. I get a single pin with schmitt-triggered 3V3 noise
> from Fredriks board and do edge detection, cycle counting etc in the
> FPGA. And provide the mixer with the result using the interface above.

By the way, have you tried hooking up the arrgh board instead? It should
work pretty much as a drop-in replacement (except maybe for that voltage
divider) but according to Fredriks results speed things up quite a bit.

>> Yes yes yes, I'll learn about FPGAs.  Promised.  Next year or so:-)
>
> Scream if there are any things that looks confusing.

You bet:-)


Cheers,

    Benedikt

-- 
Benedikt Stockebrand,                   Stepladder IT Training+Consulting
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