Trouble to verify ECDSA signature, NIST P-256

[Yann Garcia]

Hello,

Oh yes, forgot it, sorry!
In my sample, q is the public key.

Thanks a lot

Best regards,

Yann Garcia
Senior Software Engineer
Microsoft MCAD.net Certified
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On Mon, 26 Nov 2018 at 00:47, NIIBE Yutaka <gniibe at fsij.org> wrote:

> Yann Garcia <garcia.yann at gmail.com> wrote:
> >
> q=hex_to_data("AC529F186F485D194EBE3677EA9FD1D7E7280648081A01686B3E78528D8AA5C6DC44DB3E54EEF45BA7EE989572D1DC0F83FF071E30B1EE5972D52D22D204A0AD",
>
> I think this representation is...
>
> [...]
> > And here was the issue: I got the error message "gcrypt/Not implemented"
>
> ... not supported by libgcrypt.
>
> For NIST P-256, only standard encoding (prefixed by 0x04, followed by X
> in MPI, then, Y in MPI [0]) is supported.  If not, it results an error
> in _gcry_ecc_os2ec by GPG_ERR_NOT_IMPLEMENTED (Not implemented).
>
> Just put the prefix "04" to your representation, if it's composed by X
> and Y in big endian.
>
> [0] http://www.secg.org/sec1-v2.pdf
> SEC 1: Elliptic Curve Cryptography (Version 2.0)
> 2.3.3 Elliptic-Curve-Point-to-Octet-String Conversion
> --
>
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