---------- Forwarded message ----------
From: gnu cry <gcry...@gmail.com>
Date: Thu, Dec 7, 2017 at 12:23 PM
Subject: Elliptic curve point multiplication with libgcrypt
To: gnupg-users@gnupg.org
Hi gpg hackers!
I want to implement an elliptic curve point multiplication (Q=dG) operation
with libgcrypt. I attach my code but my program doesn't work and it has
many errors. I comment the workflow of my program in the attached code.
my question is how do you implement Q=dG in C with libgcrypt? any idea
about my mistakes and how should I fix them?
Thanks
//ec.c
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <gcrypt.h>
//select and insert key and curve parameters
char *key521 =
"(key-data\n"
" (public-key\n"
" (ecc\n"
" (curve NIST P-521)\n"
" (q
#00F2271E305679EBF9D7673FBF75EEA22E90D100A9E0B5DE30C500411E91710D05826F17F2C33A9527CC6799553C626C015ED666F63A4D5CEB27CDBE61F34DB0AF#)\n"
" )\n"
" )\n"
" (private-key\n"
" (ecc\n"
" (curve NIST P-521)\n"
" (d
#00BC9D8FD5D0AC1C91C04A1E0A5B6A89229924AAD20E23C5F5E3FE702C3C4633E325D2084DC0CE2005A88FF0512E0CACC271DF3279865DC2C33FCF573F7788278E#)\n"
" )\n"
" )\n"
"\n )";
// workflow for calculating of Q=dG
int main() {
gcry_check_version(NULL);
gcry_mpi_point_t Q,G; //define and hold two elliptic curve point
gcry_mpi_point_release(G);
gcry_mpi_t d; //define the scalar (d)
gcry_sexp_t dsex; //define an S-expression variable
gcry_sexp_sscan(&dsex, NULL, key521, strlen(key521)); //set dsex =
d in key521 data structure
gcry_sexp_release(dsex);
d= gcry_sexp_nth_mpi(dsex, 1, GCRYMPI_FMT_USG); // convert
from S-exp to MPI format
char curvename= "NIST P-521"; //define curve name
gcry_ctx_t context; //define a context (ctx)
gcry_mpi_ec_new(context, dsex, curvename); //set context
gcry_ctx_release(context);
gcry_mpi_ec_mul(Q,d,G,context); // calculate Q=dG
}
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