CryptographicEngine::SignHashedData not implemented error

I encountered an error while using cppwinrt. When I use CryptographicEngine::SignHashedData function to sign a hash value, it returns WinRT originate error - 0x80004001 : 'not implemented'.

Here is the code:

#include "pch.h"

using namespace winrt;
using namespace Windows::Foundation;
using namespace Windows::Security::Cryptography;
using namespace Windows::Security::Cryptography::Core;
using namespace Windows::Storage::Streams;
using namespace std;

int main()
{
    init_apartment();
    IBuffer buffKeyPair; 
    IBuffer buffPublicKey;
    IBuffer nullBuff(nullptr);
    uint32_t asymmetricKeyLength = 512;
    hstring strMsg = L"zzp yes!";
    hstring strAsymmetricAlgName = AsymmetricAlgorithmNames::RsaPkcs1();
    hstring strAlgNameH = HashAlgorithmNames::Md5();
    AsymmetricKeyAlgorithmProvider objAlgProv = AsymmetricKeyAlgorithmProvider::OpenAlgorithm(strAsymmetricAlgName);
    CryptographicKey keyPair = objAlgProv.CreateKeyPair(asymmetricKeyLength);
    IBuffer buffUtf8Msg = CryptographicBuffer::ConvertStringToBinary(strMsg, BinaryStringEncoding::Utf8);
    HashAlgorithmProvider objAlgH = HashAlgorithmProvider::OpenAlgorithm(strAlgNameH);
    IBuffer buffHash = objAlgH.HashData(buffUtf8Msg);
    IBuffer signedBuff = CryptographicEngine::SignHashedData(keyPair, buffHash);
    hstring strHashHex = CryptographicBuffer::EncodeToHexString(signedBuff);
    std::cout << "the strHashHex is: " << winrt::to_string(strHashHex) << std::endl;
}

Could you please help me find the problem? Thanks!

I'm not too experienced in this space, but I think I figured out a couple issues. This is happening because you aren't using an algorithm that can be used for signing, and you aren't using a hash algorithm compatible with it. The docs seem a bit... sparse... in this regard, but the algorithm names that have "sign" in them looked promising.

After a little experimentation, I got this to work.

using namespace Windows::Security::Cryptography;
using namespace Windows::Security::Cryptography::Core;
using namespace Windows::Storage::Streams;
using namespace std;

int main()
{
    init_apartment();

    auto algo_name = AsymmetricAlgorithmNames::RsaSignPkcs1Sha1();
    auto asymmetric_provider = AsymmetricKeyAlgorithmProvider::OpenAlgorithm(algo_name);
    auto keyPair = asymmetric_provider.CreateKeyPair(512);

    auto md5_hasher = HashAlgorithmProvider::OpenAlgorithm(HashAlgorithmNames::Sha1());
    auto buffHash = md5_hasher.HashData(
        CryptographicBuffer::ConvertStringToBinary(
            L"Hello world", BinaryStringEncoding::Utf8));
    auto signature = CryptographicEngine::SignHashedData(keyPair, buffHash);

    auto publicKey = asymmetric_provider.ImportPublicKey(keyPair.ExportPublicKey());
    auto match = CryptographicEngine::VerifySignatureWithHashInput(
        publicKey, buffHash, signature);
}

Notice that I used RsaSignPkcs1Sha1 which seems to indicate that this algorithm can do signing. Also, for the hash algorithm, I used Sha1. Using Md5 gave a different runtime error (and Md5 is pretty weak, anyway). I also added the code to show how to use your key pair's public key to verify the signature.