Hello list
I became aware of EC_GROUP_precompute_mult when I had to generate a lot
of public keys fast. It speeds up this process by about a factor of 5.
So it's been very useful for me.
I've been researching if EC_GROUP_precompute_mult has any effect when
verifying ECDSA signatures using ECDSA_verify, and my results are
somewhat inconclusive. I see a small speedup, around 2-5%, but I'm not
sure what the reason is for this.
I can see the code that verifies signatures uses EC_POINT_mul, but I
don't see a significant speedup as I did when using it to just generate
public keys (q and m set to NULL in EC_POINT_mul). I can see that in the
OpenSSL signature verification code q and m are not NULL in
EC_POINT_mul, so it makes sense why the speedup wouldn't be as great as
when they are NULL (since precomputations are only made for the
generator point of the curve). But I don't understand why the speedup
becomes so small when q and m are set, as I still did see a 5x speedup
(from roughly 1000 us per execution of EC_POINT_mul to roughly 200 us)
when q and m are NULL.
Should there, in theory, be any reason for EC_GROUP_precompute_mult to
speed up signature verification?
Thanks!
/Rune
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