C++ DLL with simple standard function

I need a C++ DLL which can be called from other .Net program like C#. The DLL need 4 functions: 1. Read a String from Registry (I've already solved this one) 2. Write a String to a specific Registry 3. Encode a String using RSA algorithm (Other standard text encrypting is also acceptable) 4. Decode a String using the same algorithm as function 3. You will got a string like this: 12343|xxxx|23424,with "xxxx" is a integer in String. You need extract "xxxx" value and return xxxx+1 as a String. All code must be compatible with visualstudio 2017 Here's the one I've code for function 1. But I have lack of knowledge in C++ so it's better to get help from you talented guy.