China loathes AirDrop so much it's publicized an old flaw in Apple's P2P protocol

The article explains that AirDrop's anonymity can be undermined because Apple IDs and phone numbers are hashed in a way that attackers (or state actors with candidate lists) can reverse using rainbow-table-style techniques; Chinese authorities have flagged and may be leveraging this weakness for surveillance, while researchers recommend cryptographic fixes (e.g., robust Private Set Intersection) though Apple has not implemented them.