Serve over HTTPS. Use Chrome on Android with NFC.
Write to tag converts to a compact #pgp= URL and writes URL + full armor MIME;
Write to server stores the key in D1; pointer URL is /{sha256} on this host.
Tag Read
Remove Card
Browser wipe is limited
Chrome Web NFC cannot zero the raw NDEF file byte-by-byte. A quick clear overwrites as much
of the message area as the browser allows, then sets an empty NDEF message.
In this browser: keep tapping until complete — overwrite then empty message. Stale bytes can still show in TagInfo.
Web NFC Bridge app: reads the full file size from the tag, zeros all bytes, verifies, and shows wipe progress.