Replacing Internet layer from tcp/ip stack and insert our own cyptography in it [on hold]

How can i replace Internet layer i.e ipv4 and add my own cryptography in it. I am doing this as a college project so if any answer to this please let me know. To be exact my topic is "Securing tcp/ip communication with cryptography" and my professor has asked me to find a way to replace internet layer from tcp/ip stack and insert my own cryptography.