Latest posts of: chizisch

Hello,

I'm trying to generate a public key from a private one using the bitcoin library secp256k1 https://github.com/bitcoin-core/secp256k1 in C++:

Code:

    // private key
    std::string privateKey = "baca891f5f0285e043496843d82341d15533f016c223d114e1e4dfd39e60ecb0";
    const char* cPrivateKey = privateKey.c_str();

    // creating public key from it
    secp256k1_context  *signingContext = secp256k1_context_create(SECP256K1_CONTEXT_SIGN);
    secp256k1_pubkey pkey;

    unsigned char *seckey = (unsigned char*) malloc(privateKey.size() * sizeof(unsigned char));
    std::copy(cPrivateKey, cPrivateKey + privateKey.size(), seckey);

    if (secp256k1_ec_pubkey_create(signingContext, &pkey, seckey) == 0) throw "Creation error";

    // print the result in hex
    std::stringstream ss;
    for (int i = 0; i < 64; ++i)
    {
        ss <<  std::setw(2) << std::hex << (0xff & (unsigned int)pkey.data[i]);
    }

    std::cout << ss.str() << std::endl;

    // parsing the result
    std::string pkey_data  = ss.str();
    secp256k1_context *noneContext = secp256k1_context_create(SECP256K1_CONTEXT_NONE);
    secp256k1_pubkey pubkey;

    if (secp256k1_ec_pubkey_parse(noneContext, &pubkey, pkey.data, 64) == 0) std::cout << "Couldnt parse using pkey.data" << std::endl;
    if (secp256k1_ec_pubkey_parse(noneContext, &pubkey, pkay_data, pkey_data.size()) == 0) std::cout << "Couldnt parse using hex public key " << std::endl;

The output:

Code:

1b9e55408c5141414e8337adef57ead18f62444fdf5f8c897d0dc812696a6141a919254d3e750075a2a9ba32dc4ed30c84e65f27e431b59b94a2aafe3e80a974
Couldnt parse using pkey.data
Couldnt parse using hex public key

The idea is to parse the public key from the generated one to see if it is really correct. Also, i tried using openssl with the same private key and i get a different public key from the private one using ecdsa secp256k1..

Any help or example on how to use the library in C++ is more than welcome.

Thank you Grin