ECDSA using SecByteBlock key pairs

Question

I have implemented ECDH, and both private and public are of type SecByteBlock, now I am trying to implement ECDSA with SHA256 using these keys.

Assuming that pubA and privA are already generated and there are SecByteBlock instances, how can I use them in ECDSA?

Thank you in advance!

OID CURVE = secp256r1();
AutoSeededX917RNG<AES> rng;

// Elliptic Curve Diffie-Hellman
ECDH < ECP >::Domain dhA( CURVE );

SecByteBlock privA(dhA.PrivateKeyLength()), pubA(dhA.PublicKeyLength());
dhA.GenerateKeyPair(rng, privA, pubA);

// Elliptic Curve Digital Signature Algorithm
ECDSA<ECP, SHA256>::PrivateKey privateKey;
DL_GroupParameters_EC<ECP> params(ASN1::secp256k1());

privateKey.Initialize(rng, params);        

// Generating private key
ECIES<ECP>::PrivateKey privateKey;
privateKey.Initialize(rng, ASN1::secp160r1());

// Generating matching public key
ECIES<ECP>::PublicKey publicKey;
privateKey.MakePublicKey(publicKey);

ECDSA<ECP>::Signer signer(privateKey);

ECDSA<ECP>::Verifier verifier(publicKey);

Answer 1

I don't think this is a good idea. You should use the ECDSA class to create the keys. However, here it is.

#include "cryptlib.h"
#include "eccrypto.h"
#include "secblock.h"
#include "filters.h"
#include "integer.h"
#include "osrng.h"
#include "files.h"
#include "oids.h"
#include "sha.h"

#include <iostream>
#include <stdexcept>

int main(int argc, char* argv[])
{
    using namespace CryptoPP;

    try
    {
        const OID CURVE = ASN1::secp256r1();
        AutoSeededRandomPool prng;

        ECDH <ECP>::Domain dh(CURVE);

        SecByteBlock privA(dh.PrivateKeyLength()), pubA(dh.PublicKeyLength());
        dh.GenerateKeyPair(prng, privA, pubA);

        const Integer x(privA.begin(), privA.size());

        ECDSA<ECP, SHA256>::PrivateKey privateKey;
        privateKey.Initialize(CURVE, x);

        bool valid = privateKey.Validate(prng, 3);
        if (valid == false)
            throw std::runtime_error("Private key is not valid ECDSA key");

        std::cout << "Private key is valid ECDSA key" << std::endl;
    }
    catch (const std::runtime_error& ex)
    {
        std::cerr << ex.what() << std::endl;
        std::exit(1);
    }

    return 0;
}

And:

cryptopp$ g++ test.cxx ./libcryptopp.a -o test.exe
cryptopp$ ./test.exe
Private key is valid ECDSA key

More information is at Elliptic Curve Digital Signature Algorithm on the Crypto++ wiki.