From 36cebf25d0e0f24cf63be4380ccb5d03da726a74 Mon Sep 17 00:00:00 2001 From: Christophe Besson Date: Mon, 7 Sep 2026 17:50:28 +0200 Subject: feat(chat): encrypt group chat under per-device epoch keys (MNP 2.0) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 Claude-Session: https://claude.ai/code/session_01TZZxYjz8YeWRz13xDi8LJr --- .../src/meshbay_hub/static/chat-app-settings.js | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-) (limited to 'packages/meshbay-hub/src/meshbay_hub/static/chat-app-settings.js') diff --git a/packages/meshbay-hub/src/meshbay_hub/static/chat-app-settings.js b/packages/meshbay-hub/src/meshbay_hub/static/chat-app-settings.js index 96fc52f..1eba59a 100644 --- a/packages/meshbay-hub/src/meshbay_hub/static/chat-app-settings.js +++ b/packages/meshbay-hub/src/meshbay_hub/static/chat-app-settings.js @@ -17,7 +17,8 @@ import { FolderPickerField } from './folder-tree.js'; * has to be on a read-write root. The picker greys out the rest rather than * letting the node's refusal arrive after the fact. */ -function ChatSettings({ roots, dirs, settings, saveDirectories, transport, signFn }) { +function ChatSettings({ roots, dirs, settings, saveDirectories, transport, + signFn }) { const { busy, msg, run } = useSaver(); const [directory, setDirectory] = useState(settings.chatDirectory || ''); const [linkPreview, setLinkPreview] = useState(settings.chatLinkPreview !== false); @@ -59,6 +60,19 @@ function ChatSettings({ roots, dirs, settings, saveDirectories, transport, signF label=${t('settings_app.chat_link_preview_label')} />

${t('settings_app.chat_link_preview_hint')}

+ ${/* Not a toggle: chat is always encrypted (MNP 2.0), so there is + nothing here to turn on. What an operator may want is to move the + key on deliberately — the removals that matter already do it by + themselves. Stated rather than left invisible, because "is my chat + encrypted?" is a question people ask of a settings pane. */ ''} +
+

${t('settings_app.chat_encrypted_always')}

+ +

${t('settings_app.chat_rotate_epoch_hint')}

+
${msg && html`

${msg}

`} `; -- cgit v1.2.3