HealthLog/docs/ops/encryption-key-rotation.md

Encryption-key rotation

HealthLog encrypts sensitive at-rest data (Withings tokens, AI provider keys, notification channel configs, web-push subscription secrets, VAPID private keys, etc.) with AES-256-GCM under a per-deployment key. v1.4 introduces a versioned key format so the key can be rotated without downtime and without re-encrypting every row by hand.

Format

Layout	Marker	Where
Versioned (new)	<keyId>.<base64(iv || tag || ciphertext)>	All new writes
Legacy (v1.3.x)	<base64(iv || tag || ciphertext)>	Existing rows until rotated

<keyId> matches [A-Za-z0-9_-]{1,32} and indexes into the ENCRYPTION_KEYS JSON map. Decryption tries the versioned format first; if no . is present or the prefix isn't a known id, the row is treated as legacy and decrypted under v1 (the synthetic id assigned to the existing ENCRYPTION_KEY).

Why a separate v1 is required. Legacy ciphertexts have no key id, so the only way to identify them is "no . in the value". If you remove the v1 entry from ENCRYPTION_KEYS before every legacy row has been rotated, those rows can't be decrypted any more — the active key won't match the original ciphertext. The decrypt path now refuses to silently fall back to the active key in that scenario; it throws a clear error.

Rotating from v1.3.x to a new key

1. Generate the new key on a machine with openssl:

   openssl rand -hex 32
   

2. Update environment variables. Keep the existing ENCRYPTION_KEY in place — it's still needed to decrypt legacy rows during the transition:

   ENCRYPTION_KEY="<old key, unchanged>"
   ENCRYPTION_KEYS='{"v1":"<old key>","v2":"<new key>"}'
   ENCRYPTION_ACTIVE_KEY_ID="v2"
   

   Restart the app. New writes are now encrypted under v2; existing v1-keyed and legacy bare rows still decrypt because the v1 entry is retained.

3. Run the rotation script to re-encrypt every registered encrypted column under the new active key:

   pnpm dlx tsx scripts/rotate-encryption-key.ts v2
   

   The script is idempotent — running it again is a no-op for rows already prefixed with v2.. It rotates every column in the canonical registry (src/lib/crypto/encrypted-columns.ts), which covers the *Encrypted columns plus the ones whose names say nothing about their contents: IntegrationStatus.lastError, CoachMessage.encryptedContent, NotificationChannel.config, the OAuth accessToken / refreshToken columns, the web-push p256dh / auth secrets, the idempotent-replay IdempotencyKey.responseBody, and DataBackup.data — the whole-account backup blob.

   Read three things off the output before going further:

   • the per-column line, scanned / rotated / errors / dropped. scanned counts the rows that hold ciphertext in that column, not every row of the table. Treat errors > 0 as a hard failure and re-run after fixing the cause. A dropped count is only ever a cache row the run could not read and deleted rather than leave unreadable.
   • Columns walked: N/M registered. The two numbers must match.
   • a NOT WALKED block, if one appears. It lists registered columns this run skipped, and the run exits non-zero. Rotation is incomplete; do not go on to step 4.

   Two guard tests keep the registry honest in CI: one scans the schema for *Encrypted columns, the other derives the ciphertext-bearing columns from the Prisma write payloads, which is what catches a column that holds ciphertext under an ordinary name.

4. Confirm nothing is left on the old key, THEN drop it. This is the step that destroys data if it is taken on a bad signal, so check the corpus rather than the absence of complaints. Either re-run the script — a clean second pass reports rotated=0, errors=0 and a full Columns walked line — or open Admin → Encryption and confirm the status view reports zero rows outside the active key. Both read the same registry the rotation walks.

   A zero only means "nothing left" when the run also says it walked every registered column. A zero from a run that skipped columns means "never looked", and dropping the old key on it makes those rows permanently undecryptable — decrypt() is fail-closed and there is no recovery path. Only once the corpus reads clean:

   ENCRYPTION_KEYS='{"v2":"<new key>"}'
   ENCRYPTION_ACTIVE_KEY_ID="v2"
   # ENCRYPTION_KEY can now be removed
   

   Restart. The legacy single-key fallback is now disconnected; only v2 exists.

Backups are covered, and were not always. DataBackup.data holds every weekly disaster-recovery snapshot and every uploaded pack, encrypted like everything else but under a column called data. It was outside the registry until v1.38.6, so a rotation before that release reported zero rows remaining without ever reading a backup. If you rotated on an older release and dropped the previous key, the stored backups are encrypted under the key you removed: put that key back into ENCRYPTION_KEYS and re-run the rotation on this release before removing it again.

Adding a third key (v2 → v3)

Same procedure, just shift the labels — keep v2 in the map until a full run (every registered column walked) reports zero v2.-prefixed rows remaining.

ENCRYPTION_KEYS='{"v2":"<old>","v3":"<new>"}'
ENCRYPTION_ACTIVE_KEY_ID="v3"
pnpm dlx tsx scripts/rotate-encryption-key.ts v3
ENCRYPTION_KEYS='{"v3":"<new>"}'

Rollback

Important. Once the rotation script has run, ciphertexts in the database start with v2. (or whatever the active id is). The pre-PR v1.3.x image cannot read that prefix — it expects bare base64 — and calling decrypt() on those rows will throw.

If you need to revert to the pre-rotation image:

• Either keep the new image. The new code reads both formats, so most rollback scenarios don't need to undo rotation.
• Or, if you must run the old code, restore a database backup taken before the rotation script ran. There is no script to convert v2.-prefixed rows back to legacy format — by design, rotation is a forward-only operation.

This is why we recommend running the rotation in a window where you have a fresh DB snapshot and the new image has been smoke-tested in production for at least 24 hours.

Troubleshooting

• Encryption key id 'v1' is not configured — the database still contains v1.-prefixed rows but v1 was removed from ENCRYPTION_KEYS. Re-add the key, run the rotation script, then remove again.
• Found a legacy-format ciphertext but no v1 key is configured — same cause for legacy bare-base64 rows. Restore ENCRYPTION_KEY (or add a v1 entry to ENCRYPTION_KEYS) and run the rotation script before removing it.
• Refusing to rotate: argv key id ... does not match the currently active id ... — pass the same id you set in ENCRYPTION_ACTIVE_KEY_ID. The guard prevents accidental re-encryption to a non-current key.