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Chat messages are sealed with AES-256-GCM under a key derived per group, per
epoch, per *device*, and signed over the ciphertext with the device key the
node pinned. The node relays and archives; it cannot read a message.
There is no switch. MNP goes to 2.0 and MNP_MIN_SUPPORTED moves with it, so a
1.x peer is refused at the handshake with `version_too_old` rather than
admitted and then unable to speak. An opt-in flag was designed and rejected:
every node is a test node, so it would have bought nothing and left a plaintext
branch reachable — C6's lesson one feature later. A test reads the source and
refuses any code that consults a `chat_encrypted` setting.
Not Sender Keys, and `senderkeys.py` is now documented as unused. With
distribution under the group key and a node that serves history to devices
which were not present, the node must retain each chain's earliest key, and a
chain key at iteration i yields every message key from i on by pure HKDF —
forward secrecy is zero either way. What the ratchet was left buying was
stateful client code with silent failure modes, three of them reproduced: any
member could sign as any other, a second device dropped the first's chain, and
the skipped-key cache grew without bound. The reasoning is in
docs/chat-sender-keys.md, which is the specification and the decision record.
Epochs, not rotation: the epoch key is wrapped under the group key at delivery
and never stored under it, so `gek_rotate` is a re-wrap. A group-key-derived
archive key would have made every message ever sent unreadable on the first
`member unpin`, which is the documented step after removing a member. A new
epoch opens on member revoke/unpin, device revoke and `gek_rotate`; old epochs
are kept and still delivered, so history stays readable to everyone who could
already read it, and nothing anywhere deletes one.
Three prerequisites this needed, each a live defect on its own:
* The peer registry was keyed by user_id, so one account's second device
evicted the first and the broadcast skipped recipients by account — a
person's phone never saw what they typed on their laptop.
* The handshake authenticated an account, never a device. `device_hello`
(additive, signed, refused unless the key is a live device of this account in
the node's own roster) is what lets the node refuse a member claiming
somebody else's key.
* `_admin_exec_file_delete` authorized against the exact uploading key, so
device linking had already broken deleting your own file from your other
device. It now authorizes against any non-revoked device of `uploader_id`.
Found by driving the real panel over the real transport, not by reading source:
`chat_keys_resp` was routed by arrival order and handed to an unanswered
`media_meta_req` — the original frozen-tab defect in a message type that did
not exist when that probe was written. And `_asText` had been deleted with an
unrelated helper beside it; its only caller sits inside a promise the panel
catches, so every conversation rendered empty with nothing in the console.
Existing node data is migrated by QE/migration/migrate_chat_encryption.py
(not versioned, per the QE rule), run with the node stopped.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TZZxYjz8YeWRz13xDi8LJr
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Typing a message froze the Chat tab: the composer stopped taking clicks and
keystrokes, the message never appeared, and it was there all along on the next
visit to the tab.
The node answers a chat message with a bare {"type": "ack"} -- no request id,
no type of its own -- so _dispatch had nothing to match it on and left it to
the arrival-order guess at the end of the function. That guess is wrong the
moment anything else this browser asked for is still waiting: the ack went to
*that* request, and the chat send waited out _sendAndWait's own 30s timeout.
Since the composer is disabled while a send is in flight, that reads as a
frozen tab; the node had stored the message and answered, into somebody else's
promise.
An outstanding request is the ordinary case, not a rare one. The node refuses
an unknown file_id with a bare `error`, which names no request either and so
reaches none, leaving the Videos tab's media_meta_req in _pending for the full
30s. That is the one that was live when this was found.
- `ack` is now matched by request type: chat_msg, or the keypair-bundle store
and delete, which name themselves in `detail`. A node naming neither still
has its reply placed rather than dropped.
Every line of chat-app.js is correct and every routed message in transport.js
is routed correctly -- the defect is in the seam, so tests/harness/
chat_send_probe.py drives the two together: the real ChatPanel over the real
MeshBayTransport, with only the DataChannel replaced by a stand-in answering
what the node answers. test_chat_send.py asserts against it, and with the fix
reverted all three of its tests fail on the three visible halves of the defect
-- the composer still disabled, the message absent, and the ack resolving the
unrelated request.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GFF4BL8VSKrghkSLzCrTVs
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