On Tue, Oct 9, 2012 at 12:29 PM, Rune K. Svendsen <runesv...@gmail.com>wrote:
> 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. > EC_GROUP_precompute_mult precomputation is based only on common group parameters, not on the specific key. It would be possible to speed up ECDSA verification similarly by doing something like that on a per-key level, but it would only help if you verify multiple signatures signed by the same key. That's why it is currently not supported by the OpenSSL API -- it would be a bit cumbersome to use properly. Bodo
