How to start developing a VPN service?

Question

VPN

Hello, we are planning to develop a VPN service for Windows, Mac, Android, iOS. We plan to do it on the Xamarin/.NET Framework.
What would you recommend for development?
How many programmers should work on a project, one or more?
Where is it better to start, with desktop programs or applications?
What difficulties can you face when developing a cross-platform application?
The main thing for me is to make my applications, of course, based on ready-made solutions .. with ready-made protocols.

Answer 1

It is good to start working with encryption with the development of cryptomathematics.
She will immediately put everything in its place. If you can then keep going.
In parallel, you can read the classics in the originals, such as OpenVPN, IPSEC.
Try to find problems in OpenVPN, then compare your achievements with the results of a code audit by professionals (as you know, money was raised for an OpenVPN audit).

Answer 2

If such questions arise, then it is better to forget about this idea :)

Answer 3

How about .net core. Just wait for the second version, they should be published in the spring.

Answer 4

Excuse me, do you want to write a client for a ready-made protocol, do you plan to develop your own? If the latter, then you need to start with the design of the protocol, and you will always have time to turn the whistle ... the searchers.