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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>