openssl-double-ec-test.c

#include <stdio.h>
#include <stdlib.h>
#include <openssl/ec.h>
//#include <openssl/ecdsa.h>
#include <openssl/obj_mac.h>

int main()
{
  BN_CTX *bn_ctx = BN_CTX_new();

  EC_GROUP *ec = EC_GROUP_new_by_curve_name(NID_X9_62_prime256v1);

  EC_POINT *p, *r;
  p = EC_POINT_new(ec);
  r = EC_POINT_new(ec);

  BIGNUM *x, *y;
  x = BN_new();
  y = BN_new();
  int on_curve = -1;

  char *x_str = "c97445f45cdef9f0d3e05e1e585fc297235b82b5be8ff3efca67c59852018192";
  char *y_str = "b28ef557ba31dfcbdd21ac46e2a91e3c304f44cb87058ada2cb815151e610046";
  BN_hex2bn(&x, x_str);
  BN_hex2bn(&y, y_str);
  EC_POINT_set_affine_coordinates_GFp(ec, p, x, y, bn_ctx);

  // To get [xy]_str into dec not hex for initial value.
  EC_POINT_get_affine_coordinates_GFp(ec, p, x, y, bn_ctx);
  x_str = BN_bn2dec(x);
  y_str = BN_bn2dec(y);
  on_curve = EC_POINT_is_on_curve(ec, p, bn_ctx);

  printf("Before:\n- x = %s\n- y = %s\n- on curve: %d\n", x_str, y_str, on_curve);

  EC_POINT_dbl(ec, r, p, bn_ctx);

  EC_POINT_get_affine_coordinates_GFp(ec, r, x, y, bn_ctx);
  x_str = BN_bn2dec(x);
  y_str = BN_bn2dec(y);
  on_curve = EC_POINT_is_on_curve(ec, r, bn_ctx);

  printf("After:\n- x = %s\n- y = %s\n- on curve: %d\n", x_str, y_str, on_curve);

  return 1;
}