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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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The passphrase derives two independent client-side values: auth_key (the
hub verifier) and bundle_key (AES-GCM key for the per-node identity
bundles, which live on nodes and never on the hub). Changing or
recovering a passphrase is therefore two operations — swap the hub
verifier, and re-wrap every reachable node's identity bundle.
Flow A — change a known passphrase (Profile page)
- POST /v1/users/password re-proves the current passphrase, swaps
pw_hash/salt/version, revokes every refresh token and returns a fresh
pair so the tab that made the change stays signed in.
- MeshBayTransport.rewrapAllNodes: for every group's online node, connect
with the old key, read the identity off the handshake, store it back
under the new key. Returns updated / unreachable / failed so the UI can
point at the operator-unpin fallback for the gaps. Always-shown
confirmation dialog listing reachable and unreachable groups.
Recovery key
- keyderive.js generateRecoveryKey (32 random bytes, grouped Base32) and
deriveRecoveryKey (HKDF-SHA256, domain meshbay:recovery:v1:<username>).
- Every per-node identity gets a second copy wrapped under the recovery
key: keypair_bundles.bundle_enc_recovery (node-only column, added in
_SCHEMA_KEYPAIR and via a PRAGMA-guarded ALTER for existing DBs),
carried on keypair_bundle_store / _resp. MNP 0.13 -> 0.14, additive.
- session.recoveryKey is persisted in IndexedDB (slot rk) and lazy-loaded
on connect, so a group joined in any later session still leaves a
recovery copy.
- Shown once at registration; optionally folded into the verification
e-mail as a pass-through the hub never stores or logs, with an opt-out.
- Profile -> Recovery key re-loads R and backfills every reachable node
via rewrapAllNodes in bundleKey mode (no passphrase re-entry).
Flow B — recover a lost passphrase (#/reset, linked from sign-in)
- POST /v1/users/password/reset-request {username, email}: both must be
the pair on file, checked against the blind email_hash (never
decrypted). A mismatch — wrong e-mail, unknown username, non-active
account — takes the identical no-op path (no code, no mail, same 200),
so it reveals nothing and cannot be used to spray reset mail from a
username alone. 5/min, 1-hour single-use code.
- POST /v1/users/password/reset {username, code, new_auth_key}: same
expiry / attempts / single-use checks as e-mail verification; revokes
every session and deletes every registered device key so a stored one
cannot sign back in past the reset.
- ResetPasswordPage: request code -> code + optional recovery key + new
passphrase -> reset + sign-in -> fan-out. connect() falls back to the
recovery-wrapped copy when the passphrase key cannot open bundle_enc.
Without a recovery key: sign-in is restored and each group needs the
operator-unpin fallback.
Supporting fixes (found in live testing)
- member unpin now also deletes the keypair bundle; connect() mints a
fresh identity when handed a bundle it cannot open (unless _rewrapOnly,
set by rewrapAllNodes), so a rejoin completes instead of dead-ending
before the invite-code prompt.
- A browser with no bundle key gets a passphrase prompt on the group page
instead of a "go back to the browser you registered on" message.
- RegisterPage / LoginPage / ResetPasswordPage trim the username so every
key derivation matches the hub's stored form.
Docs: docs/auth-confirm.md. Locale keys across all ten catalogues.
Tests: test_password_change, test_password_reset, test_recovery_email,
test_recovery_key, test_rewrap_fanout, test_bundle_store_recovery, plus
additions to test_admin_ops_mnp and test_webrtc_transport. Hub suite 492
passed; node suite 741 passed (the lone test_packaging_units failure is a
pre-existing RPM-spec flake, reproducible on main).
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GGkxJW9br8Y9bhT8ywJ3oc
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Two things the multi-browser story made obvious.
**The backup is now opt-out.** Keys are kept, encrypted with the passphrase, on
every node whose group you join — that is what lets a second browser recover
them, and it is finding C4: a PBKDF2-protected blob on other people's disks,
attackable offline at the speed of PBKDF2, which is memory-light and therefore
cheap on a GPU. Until now everybody paid that cost, including people who will
only ever use one browser and get nothing back for it.
Settings → "Use this account on other devices". Turning it off does not merely
stop future uploads: the next connection to each node withdraws what that node
already holds (new keypair_bundle_delete, which only ever deletes the caller's
own, taken from the authenticated session and never from the message). The
warning says plainly what it costs — clearing the browser then loses everything
encrypted for that account, with no recovery, which is the point of choosing it.
Default is on. Silent, unrecoverable key loss is worse for an ordinary user than
an exposure the roadmap already tracks, but that is a judgement call and it is
now visible and reversible instead of implicit.
**Passphrase floor 8 → 12 characters, plus a strength estimate** shown while
typing, with a refusal below ~60 bits. This number matters more here than in
most applications: it is what stands between a node operator and your identity
keys. It has to live in the client — with the password split (T1) the hub never
sees a password and cannot enforce anything about one — so the UI says why it
is asking, rather than nagging.
The estimator is deliberately conservative and dependency-free: character
classes and length, penalised for repetition and for the handful of patterns
everyone tries.
Verified against the live deployment: withdrawing the backup leaves a second
browser unable to recover anything, which is exactly what it promises, and
re-enabling restores it.
Tests: 338.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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Baseline commit capturing in-progress Phase 12 work that was already present
in the working tree (uncommitted) before the Phase 11.5 security remediation
begins. Committed as-is, without review or modification, so that remediation
changes arrive as a separable diff.
Contents: BundleStore (P2P GEK + keypair bundles), password split
(auth_key / bundle_key), node Ed25519 auth (POST /v1/nodes/auth, node-scoped
JWT), GEK-HMAC handshake proof with DTLS channel binding, Ed25519 admin
challenge-response, node local admin UI rewrite, browser key persistence.
Not authored in this session — captured to establish a baseline.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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