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 https://www.openssl.org/docs/man1.1.1/man3/EC_POINT_new.html Hope this helps, Nicola Tuveri On Fri, Oct 18, 2019, 11:31 Luca Di Mauro <luca.dima...@cnit.it> 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 > > >
