Sync users between two forests - No trust relationship

Hi,
I am working on a project where I want to sync users from domain A to domain B(another forest). Both these domains(A&B) does not have trust relationship established. I have already developed sync service using DirSync control. My sync service will run on domain A. 

I want to know what it the best and secure solution/channel to sync users to domain B like:- SSL/TSL or any other option. Can anybody guide me how can I implement the same?

I am using C#.net and following namespaces:-

System.DirectoryServices, System.DirectoryServices.Protocols and system.directoryservices.accountmanagement