Addresses the Codex review and adversarial-review findings on #1383:
- TLV encoding now throws GroupTLVError.valueTooLong instead of clamping to
65535 and truncating, so an oversize group message fails to seal and
surfaces send_failed rather than shipping ciphertext recipients drop.
- Roster nicknames truncate on a Character boundary (never mid-scalar), so a
multi-byte nickname can no longer make the whole signed roster undecodable.
- Invites now bump the epoch (rotate the key) like removals, giving every
roster change a strictly-increasing epoch so out-of-order invite states no
longer last-writer-wins a just-added member back out.
- Removing a member now sends them a creator-signed roster-without-them under
a throwaway all-zero key (never the rotated key), so their client
deactivates the group and surfaces "removed" instead of going silently dark.
- /block is enforced in the group receive path: a blocked member's messages
are dropped from display and notifications, consistent with every other
inbound path.
- Media affordances are disabled in group chats (both computed sites) so the
composer can't strand a media placeholder that never sends; media-in-groups
is a documented v2 item.
- Creator signature now covers the group name and the sender signature covers
the epoch (wire-format-affecting; needs Android parity before ship).
- Explicit isGroup guard in markPrivateMessagesAsRead so read/delivered
receipts can never leak into group conversations under a future refactor.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Small encrypted crews (hard cap 16) between public broadcast and 1:1 DMs:
Protocol
- MessageType.groupMessage = 0x25: broadcast packets with a cleartext
16-byte group ID + epoch, ChaCha20-Poly1305 ciphertext (epoch bound as
AEAD AAD), inner Ed25519 sender signature over
"bitchat-group-msg-v1"|groupID|messageID|timestamp|content
- NoisePayloadType.groupInvite = 0x06 / .groupKeyUpdate = 0x07:
creator-signed group state (key, epoch, roster) 1:1 over Noise; signature
over "bitchat-group-v1"|groupID|epoch|key-hash|roster-hash and the Noise
session peer must BE the creator
- SyncTypeFlags bit 10 (groupMessage): variable-length LE bitfield widens
1 -> 2 bytes inside the length-prefixed REQUEST_SYNC TLV; old clients
ignore unknown bits and answer with types they know
- PeerCapabilities.localSupported now advertises .groups
Storage
- GroupStore: symmetric keys in the keychain, roster/name/epoch as
protected JSON in Application Support; wiped in panicClearAllData()
Behavior
- Non-members relay 0x25 like any broadcast but cannot read it; group
messages join gossip-sync backfill with the public-message window
- Receivers drop wrong-epoch envelopes, bad sender signatures, and
senders missing from the creator-signed roster
- Fire-and-flood delivery (no per-member acks in v1)
UI
- Groups open as chat windows through the private-chat sheet (virtual
"group_" peer IDs); groups section in the people sheet; /group
create/invite/remove/leave/list commands; invitees get a system message
+ notification and the group appears in their people sheet
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
