Hubert Kario writes:
> I think the openssl compile is missing the `enable-ec_nistp_64_gcc_128`
> option?

Results on the same Comet Lake of a fresh run of the script with that
option added to the Configure line:

                              op      op/s
 256 bits ecdh (nistp256)   0.0001s  12184.0
 253 bits ecdh (X25519)   0.0000s  24758.0

For comparison, results that I posted before without the option:

                              op      op/s
 256 bits ecdh (nistp256)   0.0001s  12186.0
 253 bits ecdh (X25519)   0.0000s  24753.0

Doesn't look like the option has any effect on these numbers.

I checked the OpenSSL changelog, which says this option appeared in
3.2.0 to enable faster code for P-384, so I also tried "openssl speed
ecdhp384", and for that there's an obvious difference: 682.2 ops/sec
without the option, 1824.8 ops/sec with the option.

The changelog also says that this P-384 speedup is "using Solinas'
reduction". The OpenSSL P-256 code was already doing that, obviously.

> Yes, a good implementation of X25519 is faster than a good implementation
> of P-256. But it's not an orders of magnitude difference,

I agree that it isn't a 100x difference.

> and it ignores the whole case of there being dedicated silicon for
> P-256 arithmetic that makes such comparisons moot.

I presume you mean that those comparisons are moot specifically on
machines with P-256 hardware accelerators. Is there data on what
percentages of TLS clients and servers have those accelerators?

---D. J. Bernstein

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