[lwip-devel] [patch #9823] altcp_tls_mbedtls.c: add restartable feature

[David GIRAULT]

Follow-up Comment #6, patch #9823 (project lwip):


[comment #5 commentaire #5 :]
> 
> [comment #1 comment #1:]
> > Hi Giuseppe,
> > 
> > I think the handling of the ALTCP_MBEDTLS_FLAGS_CRYPTO_IN_PROGRESS flag
must be made by the altcp_mbedtls_lower_poll() function. This allow reuse
existing cyclic TCP timer. And ensure your new function isn't called too
much.
> 
> As Simon already observed, poll mechanism call rate will be too slow.
> 
> 
> > Anyway, this patch require that the ECP calculus are made in HW (or that
sw implementation can stop at some point).
> 
> I couldn't get your point. If ECP calculus are made in HW, I think they
would be much more fast and restartable wouldn't be useful.

We currently use the STSafe crypto HW module and it take 400ms min to achieve
ECDSA signature check during TLS negotiation.

This is why I think the poll API may be enough. CPU (STM32F479) is completely
free to do other thing during this time. Too fast polling will waste CPU
cycles.

I don't check basic ECP operations timings yet, so I can't know if it's a lot
faster or not.



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