This sounds halfway related to a problem my statistics professor worked on, sending data over a shared interface without detection. Note that these scenarios as

This sounds halfway related to a problem my statistics professor worked on, sending data over a shared interface without detection. Note that these scenarios assume discrete time. "Shared randomness" might be the current noise level on some radio frequency in enemy territory. You and your receiving friend can both hear everything, but as soon as one of you starts transmitting you must have a very careful strategy to avoid detection.