Crypto++ SHA1 Function

Question

I can't figure out what's wrong with my function - it causes a breakpoint on return.

std::string generateHash(std::string source)
{
    CryptoPP::SHA1 hash;
    byte digest[CryptoPP::SHA1::DIGESTSIZE];
    hash.CalculateDigest(digest, (const byte*)source.c_str(), source.size());
    std::string output;
    CryptoPP::HexEncoder encoder;
    CryptoPP::StringSink test = CryptoPP::StringSink(output);
    encoder.Attach((CryptoPP::BufferedTransformation*)&CryptoPP::StringSink(output));
    encoder.Put(digest, sizeof(digest));
    encoder.MessageEnd();
    return output; // here
}

Answer 1

encoder.Attach((CryptoPP::BufferedTransformation*)&CryptoPP::StringSink(output));

In this line, CryptoPP::StringSink(output) is a temporary object. After this call CryptoPP::StringSink(output) no longer exists. So If you try to follow its address (encoder.Attach and encoder.Put), you will get undefined behavior. (Like you should never return the address of a local variable)

My code for reference:

 std::string generateHash(std::string source)
  {
      CryptoPP::SHA1 hash;
      byte digest[CryptoPP::SHA1::DIGESTSIZE];
      hash.CalculateDigest(digest, (const byte*)source.c_str(), source.size());
      std::string output;
      CryptoPP::HexEncoder encoder;
      CryptoPP::StringSink test = CryptoPP::StringSink(output);
      encoder.Attach(new CryptoPP::StringSink(output));
      encoder.Put(digest, sizeof(digest));
      encoder.MessageEnd();
      return output;
  }