Impressive work! The first programming class I took had us implement communication using IR LEDs between Arduinos as a final project. It's a more difficult problem than it seems at first because of all the constraints. The Arudino Uno only has 2K RAM which means you need to be very conservative with buffers. Additionally, you usually want the RNG for the two nodes to be different which means you can't just use the time to seed it and need to look for other sources of entropy like reading the voltage on an open port.