[Cryptech Tech] Noise board on Novena

[Benedikt Stockebrand]

Hi Fredrik and list,

Fredrik Thulin <fredrik at thulin.net> writes:

> I agree - SPI has it's downsides. I'll be easily swayed in the matter if you 
> can argue why some other alternative is better.
>
> As I see it, the alternatives on this levels for the speeds we are talking 
> about are SPI, I2C, UART, and bit-banging.
>
> The appealing thing about SPI, I2C and UART in my mind is that they are well 
> supported (often in hardware) among MCUs,

plus (and that's why they are so popular) they need way less pins than
parallel bit banging (byte banging? word banging?).  Fair enough, but
especially with SPI you really have to be careful if you want to deal
with a broken device properly, among other issues

That's why I used the 20 pin tiny2313 rather than an 8 pin tiny25/45/85,
but there surely isn't a one-size-fits-all answer to this.

> and other people could take a 
> entropy module speaking one of those, connect it to a Raspberry Pi (for 
> example) and start interacting with it in about 10 lines of Python code.
>
> This makes it easier for others to test, develop and audit entropy sources for 
> Cryptech HSMs. The entropy sources would also be easier to reuse in other 
> applications.

Hmm, I haven't yet had reason to do bit banging on the RasPi, but I
guess that shouldn't really be all that bad, provided that the RasPi
controls the clock---otherwise you'll have to deal with nasty timing
issues.

> Bit-banging, although preferably with less than 32 parallel data lines, would 
> probably be easier if we didn't have to care about other people, but I think 
> we should care.

We do, but if we can do away with the MCU altogether, that's also an
improvement worth the while.

> Let me hear your arguments for something else than SPI =)

So done:-)


Cheers,

    Benedikt

-- 
Benedikt Stockebrand,                   Stepladder IT Training+Consulting
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