Win32 CryptProtectData how to save output data? - c++

Question

https://learn.microsoft.com/en-us/windows/win32/api/dpapi/nf-dpapi-cryptprotectdata
How can I save the output key to the windows registry or a file? I've been trying to do this for two days now but no progress. One of the problems is that I am using Unreal Engine and they have their own string type "FString" which does not easily convert to std::string or const char*
This is the code I'm using to save to the registry, but I'm not sure if it's valid:
void SUGH1LoginWidget::SecureSaveJWTToken(FString JWT_Token)
{
#ifdef _WIN32
DATA_BLOB DataIn;
DATA_BLOB DataOut; // Key to decrypt the data. Store in windows registry.
DATA_BLOB EncryptionKey; // Uses define in ShooterGame.h to encrypt the data so that only the UGH1 application can access the token.
DWORD cbDataInput = lstrlenA((char*)TCHAR_TO_ANSI(*JWT_Token)) + 1;
DataIn.pbData = (BYTE*)ConvertFStringToCString(JWT_Token).get();
DataIn.cbData = cbDataInput;
BYTE* pbDataEncryptionKey = (BYTE*)TOKEN_ENCRYPTION_KEY;
DWORD cbDataEncryptionKey = strlen((char*)pbDataEncryptionKey) + 1;
EncryptionKey.pbData = pbDataEncryptionKey;
EncryptionKey.cbData = cbDataEncryptionKey;
// Finally save the data
CryptProtectData(&DataIn, NULL, &EncryptionKey, NULL, NULL, NULL, &DataOut);
SaveJWTDecryptionKeyToRegistry(DataOut);
#endif
}
void SUGH1LoginWidget::SaveJWTDecryptionKeyToRegistry(DATA_BLOB DecryptionKey)
{
FString Base64EncryptionKey = FBase64::Encode(DecryptionKey.pbData, DecryptionKey.cbData);
HKEY CurrentUserKey;
LSTATUS Error;
Error = RegOpenCurrentUser(KEY_ALL_ACCESS, &CurrentUserKey);
if (Error == ERROR_SUCCESS)
{
HKEY SoftwareKey;
Error = RegOpenKeyExA(CurrentUserKey, "SOFTWARE", NULL, KEY_WRITE, &SoftwareKey);
if (Error == ERROR_SUCCESS)
{
HKEY UGHStudiosSubKey;
Error = RegCreateKeyExA(SoftwareKey, "UGH Studios LLC", NULL, NULL, REG_OPTION_NON_VOLATILE, KEY_WRITE, NULL, &UGHStudiosSubKey, NULL);
if (Error == ERROR_SUCCESS)
{
Error = RegSetValueExA(UGHStudiosSubKey, "LoginTokenDecryptionKey", NULL, REG_SZ, (BYTE*)TCHAR_TO_ANSI(*Base64EncryptionKey), Base64EncryptionKey.Len());
RegCloseKey(UGHStudiosSubKey);
RegCloseKey(SoftwareKey);
if (Error != ERROR_SUCCESS)
{
UE_LOG(LogLoginWidget, Error, TEXT("The game was unable to save the login token to the registry."));
}
}
}
}
else
{
UE_LOG(LogLoginWidget, Error, TEXT("The game was unable to access the windows registry on this machine. "));
}
RegCloseKey(CurrentUserKey);
}
This is my code for loading from the registry back into an FString but it's not working properly:
std::shared_ptr<char[]> SUGH1LoginWidget::ConvertFStringToCString(const FString InputString)
{
std::shared_ptr<char[]> ptr(new char[InputString.Len()]);
TArray<TCHAR> CharArray = InputString.GetCharArray();
for (int i = 0; i < InputString.Len(); i++)
{
ptr[i] = CharArray[i];
}
return ptr;
}
PRAGMA_DISABLE_OPTIMIZATION
FReply SUGH1LoginWidget::GetJWTTokenFromRegistry()
{
TArray<uint8> DecryptionKeyBytes;
// load base64 string from registry
LSTATUS Error;
HKEY UGHStudiosSubKey;
Error = RegOpenKeyExA(HKEY_CURRENT_USER, "SOFTWARE\\UGH Studios LLC", NULL, KEY_READ, &UGHStudiosSubKey);
if (Error == ERROR_SUCCESS)
{
char buffer[8193] = { 0 };
DWORD dwLen = 8192;
DWORD dwType = 0;
Error = RegQueryValueExA(UGHStudiosSubKey, "LoginTokenDecryptionKey", 0, &dwType, (BYTE*)buffer, &dwLen);
if (Error == ERROR_SUCCESS)
{
std::string outValue = buffer;
FString decoded_string;
//FString reg_value_as_fstring = FString(outValue.length(), outValue.c_str());
uint8* decoded = malloc();
FBase64::Decode(outValue.c_str(), outValue.size(), decoded);
//:Decode(const FString & Source, TArray<uint8>&OutDest
//::Decode(const CharType* Source, uint32 Length, uint8* Dest)
//UE_LOG(LogLoginWidget, Error, TEXT("Out value: %s"), *decoded_string);
}
//Error = RegQueryValueExA(UGHStudiosSubKey, "LoginTokenDecryptionKey", NULL, NULL, buffer, size);
return FReply::Handled();
//return decoded_string;
//std::string outvalue = (char*)buffer;
}
//FBase64::Decode(, DecryptionKeyBytes)
//return FString("");
return FReply::Handled();
}
PRAGMA_ENABLE_OPTIMIZATION
What's the standard way of saving the struct data? I was tying to Base64 encrypt it and save it as a registry key. But this doesn't work.