Your phone can see dozens of WiFi networks right now. Step 3: Encryption and AnnouncementNow we encrypt our peer information using each preImage as the encryption key and announce to the rendezvous server using the publicTags as indexes. If Bob observes a similar WiFi environment, they'll generate matching publicTags and be able to decrypt Alice's peer information. Multiple ModalitiesThe system works with any categorical data, not just WiFi networks: shared interests, Bluetooth networks, cell towers, or any modality you define. Tags are withdrawn from the rendezvous server on expiry (depending on the implementation), preventing stale data and limiting tracking windows.