Could Private Information Retrieval let Nostr clients query relays without revealing who they follow? In theory, yes. In practice, Nostr's filter syntax raises hard cryptographic questions that don't have answers yet. This post asks those questions. nostr:naddr1qqgr2dnrxvcx2ctpxu6nxenpxeskyq3qklkk3vrzme455yh9rl2jshq7rc8dpegj3ndf82c3ks2sk40dxt7qxpqqqp65wu273pc