utils/TODO-crdt-e2e-encryption.md

Encrypt crdt_sync payloads end to end

what

Firebase RTDB stores every crdt_sync record in plaintext, so Google can read all app data. Encrypt record payloads on the device before push and decrypt after pull, so RTDB stays a blind relay (the "ownership" meaning of local-first: hologram.page/blog/local-first-means-three-different-things).

open decisions (ask kuhy before coding)

• Key source: derived from the shared crdt-sync password (Argon2id) or a random key stored in the OS keystore and copied to new devices.
• Migration: re-encrypt existing logs in place, or new prefix + one-time copy.
• Scope: payload only (keep HLC/ids clear for merge) or whole record.
• diet_guard's export_keys document (random data-export keys, synced as a keyring) sits in plaintext in RTDB, so Firebase can read them: it must move under E2E too, with its key source decided here first.
• tutor uses its own RTDB client (~/src/tutor/app/lib/sync/rtdb_client.dart): in or out of scope.

steps

1. Add an encrypt/decrypt seam in crdt_sync_dart/lib/src/remote_store.dart (push/pull), AEAD (XChaCha20-Poly1305), version byte per record.
2. Property test: decrypt(encrypt(r)) == r; merge result identical with and without encryption (see property-and-differential-tests skill).
3. Read path accepts plaintext and v1 records during migration.
4. Roll out app by app (todo first), bump pins, verify on the phone.

done

dart test in crdt_sync_dart passes, and firebase database:get /<prefix> | grep -c '"title"' returns 0 for every migrated app.

verify

Pixel 6a + desktop todo: edit on one, see it on the other; raw RTDB JSON shows only ciphertext.

read first

• crdt_sync_dart/lib/src/sync.dart, log.dart, remote_store.dart
• crdt_sync_flutter/lib/src/bootstrap.dart

REMOVE ME AFTER FINISH