Regarding "ec_GFp_simple_add" implementation

[ChenGuang Sun]

Found it! Thank you for the context info and pointer, Billy!

Charlie

On Sun, Aug 28, 2022 at 12:35 AM Billy Brumley <bbb at iki.fi> wrote:

> > I'm new to the ECC area and trying to understand the point addition
> here. I noticed the implementation of "ec_GFp_simple_add" is different from
> the algorithm described at Wikipedia. Does the function
> > "ec_GFp_simple_add" implement the algorithm in Wiki? Is there any
> doc/paper explaining the implementation of "ec_GFp_simple_add"?
>
> That ECC code pre-dates Wikipedia, so the answer is "no" :)
>
> I believe it is A.10.5 from P1363 or extremely similar. (A crypto standard
> from the late 90s---you'll have to do your own digging.)
>
> At a high level, it is Jacobian projective coordinates with codepath
> optimizations for mixed projective-affine inputs (if applicable).
>
> Please keep in mind the fact that this particular code uses (any form of)
> projective coordinates is only internally relevant for OpenSSL. In the
> public API, all getters / setters / etc related to projective coordinates
> were deprecated as of OpenSSL 3.0.
>
> Hope it helps,
>
> BBB
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