How to transfer as router at one NIC ?

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VisualC++

Hi, i'm stewed with my project, need help.

we have a project that can encrypt the local UDP packets and transfer to other internet server.
My local PC have one NIC only.

My project use WinpkFilter from NTKernel that through a driver at NIC to option all UDPs.
Local PC UDP<------------->NIC(encrypt option)<------------->router<------------>Internt

We want extend it can support other PC's UDP, means ohters PC sent the UDP to my local PC, my Local PC encrypt and transfer it to internet, back also. like that:
other PC UDP<------------->my local PC NIC<-------->Router<-------------->Internet


What can i do?

Very appreciate if give me some advice.

Best regards,

Huitan