Generate EC mul test vectors using OpenSSL

secp.cpp

#define OPENSSL_SUPPRESS_DEPRECATED
#include <openssl/bn.h>
#include <openssl/ec.h>
#include <openssl/obj_mac.h>
#include <openssl/objects.h>
#include <stdio.h>
#include <vector>

void check_rc(const char* where, int rc, int expected_rc = 1) {
   if(rc != expected_rc) {
      printf("%s returned %d\n", where, rc);
      exit(1);
   }
}

BIGNUM* hex2bn(const char* s) {
   auto bn = BN_new();
   int rc = BN_hex2bn(&bn, s);
   if(rc == 0) { printf("hex2bn failed"); exit(1); }
   return bn;
}

void dump(const char* what, BIGNUM* n, size_t order_bits) {
   std::vector<uint8_t> x((order_bits + 7) / 8);
   BN_bn2binpad(n, x.data(), x.size());
   printf("%s = 0x", what);
   for(size_t i = 0; i != x.size(); ++i) {
      printf("%02X", x[i]);
   }
   printf("\n");
}
void dump(const char* what, EC_GROUP* group, EC_POINT* p, BN_CTX* ctx) {
   uint8_t buf[256] = { 0 };

   size_t written = EC_POINT_point2oct(group, p, POINT_CONVERSION_COMPRESSED,
                                       buf, sizeof(buf), ctx);

   printf("%s = ", what);
   for(size_t i = 0; i != written; ++i) {
      printf("%02X", buf[i]);
   }
   printf("\n");
}

int main() {
   const auto nid = NID_secp256k1;
   auto group = EC_GROUP_new_by_curve_name(nid);

   auto bn_ctx = BN_CTX_new();

   const size_t bits = BN_num_bits(EC_GROUP_get0_order(group));
   
   printf("[%s]\n", OBJ_nid2sn(nid));
   for(size_t i = 1; i != 64; ++i) {

      EC_POINT* basept = EC_POINT_new(group);
      BIGNUM* basept_k = BN_new();
      BN_rand(basept_k, bits, BN_RAND_TOP_ANY, BN_RAND_BOTTOM_ANY);
      EC_POINTs_mul(group, basept, basept_k, 0, nullptr, nullptr, bn_ctx);

      EC_POINT* r = EC_POINT_new(group);
      BIGNUM* n = BN_new();
      //BN_set_word(n, i);
      BN_rand(n, bits, BN_RAND_TOP_ANY, BN_RAND_BOTTOM_ANY);
      BN_mod(n, n, EC_GROUP_get0_order(group), bn_ctx);
      const EC_POINT* basept_arr[1] = { basept };
      const BIGNUM* basept_k_arr[1] = { n };
      EC_POINTs_mul(group, r, nullptr, 1, basept_arr, basept_k_arr, bn_ctx);

      dump("P", group, basept, bn_ctx);
      dump("k", n, bits);
      dump("Z", group, r, bn_ctx);
      printf("\n");
   }
}