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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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`index_sync`, `index_delta` and the `handshake_ack` config payload now travel
sealed under a GEK-derived subkey (`meshbay_common/groupbox.py`, mirrored by
`sealGroup`/`openGroup` in `crypto.js`). Only `type`, `v`, `group_id` and the
ack's `node_pk`/`proof`/`sig` stay in clear — a receiver must route and
authenticate before it would trust a decryption. Verify, then decrypt.
The ack line is integrity, not confidentiality: the signed handshake transcript
names no ack field, so `is_node_admin`, `enabled_apps`, `video_root` and the
rest were authenticated by the DTLS channel alone. The index line is defence in
depth against a repeat of C1/C6 — a peer served before the handshake completes
now gets ciphertext, not filenames. Nothing against an observer, the hub, or a
member; that is the whole claim. `index_progress` stays clear (D3, counters
only). Chat is out of scope.
Failure is fatal: a payload that does not open ends the session naming the
message type — never an empty index or an empty `enabled_apps`, both of which
are legitimate states.
Version negotiation ships here too (phase 15.6, brought forward): `v` + `v_min`
on `handshake` and `handshake_challenge`, refused with `version_too_old` /
`version_too_new` / `version_unreadable`. The flag day was already being paid
for; the next breaking change now costs a refusal message.
BREAKING CHANGE: breaks the WebRTC wire every deployed client speaks. Hub and
every node must deploy together; the SPA is served by the hub, so a browser
picks up the new client on reload. See MESHBAY_NODE_PROTOCOL.md §11.1a, §13.1.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HkzbhmMmK8PqQBtGz5zCvY
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The invite flow fetched the invitee's pk_x25519 from the hub and wrapped the
GEK for whatever came back (app.js:1466, and gek-init did the same server-side).
The hub is the key directory, so a hub answering with its own key was handed the
group key by an honest member following the protocol exactly. No forgery, no
injection, nothing for the client to notice. That was H3.
The fix is not safety numbers. Nobody reads the directory any more:
- the node holds the GEK and wraps it itself, on every connection, for the
X25519 key the joiner signed with their Ed25519 identity in one transcript
(meshbay:join:v1), so the identity key vouches for the encryption key;
- identities are bound to accounts by a one-time code the hub never sees —
40 bits, single use, one account, bounded per connection AND node-wide;
- the node's own roster decides who may receive the key. Hub membership lets
someone reach a node; it no longer gets them anything. A hub that invents an
account and mints it a token is answered not_authorized_for_group.
Safety numbers would have made substitution detectable by a human who checks, at
the moment there is nothing to check against — first contact. Removing the lookup
makes it impossible, and costs the user one code to pass along.
M3 falls out of the same work. The daemon auto-pinned its own keystore key as
admin_pk_ed25519 while the browser signs with the user identity key, so every
privileged operation failed closed with a signature error that looked like a bug
somewhere else; the demo only worked because a deploy script overwrote the value.
Authority now comes from the roster, established locally by `operator pair`.
Asking the hub for the operator's key — the obvious-looking fix — would have let
the hub install itself as node administrator.
BREAKING: gek_bundle_store is deleted, not gated. No member hands the node key
material at all, so C5b becomes structural rather than an authorization to check.
Existing stored bundles are still served, so current deployments keep working.
Also:
- join_policy (invite|open) is read from node.toml, never from the hub — a hub
able to declare a group open would be handed its key. Unknown group ⇒ invite.
- admin signatures are verified against the roster on every check, so unpinning
takes effect without a restart. admin_pk_ed25519 stays readable as legacy.
- two C5b tests were rewritten, deliberately: they asserted that
gek_bundle_store demanded an operator signature, and the message is gone. They
now assert the stronger property. The file says not to fix these tests, so
this is the record of why they changed.
- a slice-1 bug found while writing slice 2: connect() never passed skEdB64, so
pairing would have failed at runtime with no test able to catch it.
Tests: 152 node+common here, including an end-to-end DataChannel run where a
member who has never held the group key redeems a code in the pre-proof window
and receives the key wrapped for a key only they can open.
Design: docs/invite-pairing-v1.md
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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The handshake proof and admin signature transcripts are built independently in
crypto.js and in meshbay_common, and compared by producing identical bytes.
Nothing on the wire carries the transcript — that is the design — but it means a
one-byte disagreement between the two implementations is invisible to every
other test while causing a total outage: no browser could complete a handshake
with any node, and every file deletion would be rejected.
Nothing else in the suite crosses this boundary. The 278 Python tests would all
still pass.
Drives the real crypto.js under node (stubbing window and crypto, which the
module body touches but these functions do not) and compares against the real
Python for the same vectors: both roles, short and empty group ids, non-ASCII
group names and filenames — TextEncoder and str.encode must agree on UTF-8 —
and field splits that would collide under naive concatenation.
Verified to actually catch a mismatch rather than trusted for passing: removing
one length prefix from the JS fails 6 vectors, and changing a single byte of the
domain-separation prefix fails 6. crypto.js restored byte-identical afterwards.
Skips when node is absent, which is a coverage gap rather than a pass — worth
making a hard failure in CI (18.4).
Tests: 168 hub+common.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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