How to compute Ethereum address from EC private key using OpenSSL

ethereum_priv2address_openssl.cpp

#include <ethash/keccak.hpp>
#include <evmc/hex.hpp>
#include <openssl/ec.h>
#include <openssl/evp.h>
#include <iostream>

#include <dlfcn.h>

int main(int argc, const char* argv[])
{
    try
    {
        const auto dl_h = dlopen("libcrypto.so.1.1", RTLD_LAZY);
        if (!dl_h)
            return 10;

        const auto bn_bin2bn_p = dlsym(dl_h, "BN_bin2bn");
        if (!bn_bin2bn_p)
            return 11;

        using bin2bn_fn = BIGNUM*(const unsigned char* s, int len, BIGNUM* ret);

        const auto bin2bn = reinterpret_cast<bin2bn_fn*>(bn_bin2bn_p);

        if (argc != 2)
            return 1;

        const auto privkey = evmc::from_hex(argv[1]);
        if (privkey.size() != 32)
            return 2;

        auto* privkey_bn = bin2bn(privkey.data(), static_cast<int>(privkey.size()), nullptr);

        auto* g = EC_GROUP_new_by_curve_name(NID_secp256k1);
        auto* pt = EC_POINT_new(g);

        const auto r = EC_POINT_mul(g, pt, privkey_bn, nullptr, nullptr, nullptr);
        if (r == 0)
            return 4;

        unsigned char buf[65];
        const auto written =
            EC_POINT_point2oct(g, pt, POINT_CONVERSION_UNCOMPRESSED, buf, sizeof(buf), nullptr);
        if (written != sizeof(buf))
            return 5;

        if (buf[0] != 0x04)
            return 6;

        const auto h = ethash::keccak256(&buf[1], 64);

        std::cout << evmc::hex({&h.bytes[12], 20});

        EC_POINT_free(pt);
        BN_free(privkey_bn);
        EC_GROUP_free(g);

        dlclose(dl_h);
    }
    catch (...)
    {
        return 13;
    }
    return 0;
}