Hi,
with traditional EC from the x coordinate alone you can't really do that, because there are always 2 possible solutions for y (in R the curve is symmetrical on the x axis).
The standards define a "compressed point" format in which you can send the coordinate x and an additional bit to select which of the 2 y solutions to pick.
You can read more about it in EC_GROUP_set_point_conversion_form at https://www.openssl.org/docs/man1.1.1/man3/EC_GROUP_copy.html
and in EC_POINT_set_compressed_coordinates at
Hope this helps,
Nicola Tuveri
On Fri, Oct 18, 2019, 11:31 Luca Di Mauro <luca.dimauro@xxxxxxx> wrote:
Hello all,
I don't know if it is the correct mailing list to ask this, so I'm
sorry if it is the wrong palce.
I'm using openssl v1.1, and I'm trying to compute both the X and Y
coordinates of an elliptic curve point starting from a single
coordinate (X or Y).
How can i perform that in C/C++ language using libssl? I searched on
google for a couple of days but i haven't found a solution.
Luca Di Mauro
