how to implement two way authentication and encryption for a web service

Background :

I am trying to build a java client for web service , the service is bound to a public IP on my router. I want to achieve encryption and authentication similar to what OpenVPN does.

How do I achieve this? My server side code will be on a dd-wrt based router. I specifically need to know what libraries / api's to use on server and should be able to work on a dd-wrt based router (C, C++, Python can work on it)开发者_如何学编程

Are there any easier alternatives which gives similar level of protection? I dont want anyone to either attack the service or do analysis on packets.