Compute EC_KEY starting from X or Y coordinate only

[Billy Brumley]

Don't do that. As I said, the library is trying to tell you that's not a
point on the secp256k1 curve.

Quickly browsing the standard, you are likely looking for the prime256v1
curve.

BBB

On Fri, 25 Oct 2019, 9.28 Luca Di Mauro, <luca.dimauro at cnit.it> wrote:

> I think it is correct because I extracted the hexadecimal string from
> a packet contained in a pcap.
>
> This compressed point is created following the ETSI TS 103 097 v1.3.1
> standard for secured communications in the vehicular communication
> context
> (
> https://www.etsi.org/deliver/etsi_ts/103000_103099/103097/01.03.01_60/ts_103097v010301p.pdf
> ).
>
> I notice that the point 'pubPoint' that I created is empty when I try
> to call 'EC_POINT_set_compressed_coordinates_GFp' function. How can I
> put a BIGNUM into an EC_POINT?
>
> Luca
>
> Billy Brumley <bbrumley at gmail.com> ha scritto:
>
> >>         EC_GROUP* group         = EC_GROUP_new_by_curve_name
> >> (NID_secp256k1);
> >
> >> "c16b4ce0532f5dc9d09114fe121d3956ae84f9eb677a0d4bdac1d3af7a91950c";
> >
> > I don't believe there's a point on secp256k1 with that x-coordinate.
> > If you check the failure reason for
> > EC_POINT_set_compressed_coordinates_GFp in the debugger, that is
> > probably what it is telling you.
> >
> > Where did this curve / x-coord pair come from?
> >
> > BBB
>
>
>
>
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