07. Loss, Compromise and Rebuild

Status: Draft.

1. Intent

The protocol keeps no state that must survive the loss of every device, so there is nothing to recover. A person who loses their devices, or whose key may have leaked, rebuilds. See ADR 0018.

2. Rebuilding

1. A new device generates a new master key (chapter 01) and becomes the first introducer.
2. Each device the person still holds is re-paired by the ceremony of chapter 02.
3. Household members re-verify the new master key in person with the person role; shared-device owner sets are updated by any remaining owner, or re-established on the principal's pairing page.
4. Standing grants are re-approved as they are next needed.

The cost is the effort of re-introducing devices and people, which the design accepts in exchange for having no shared state.

3. Abandoning a key

An abandonment is a revocation whose subject is the person's own master key, signed with that person's self-signing key by an introducer that still holds it (ADR 0039); it is gossiped like any revocation. Devices that receive it stop recognising the old key and its bindings. Nobody can abandon a key on another person's behalf, so a person who has lost every introducer has no abandonment to gossip: they rebuild (section 2), household members re-verify them and may revoke the old person role on their own devices, and devices that hear neither simply treat the old key's bindings as an unknown person's.

4. Open questions

• Whether implementations should offer an encrypted export of the local store (chapter 06 section 6) so a rebuild can restore grants and known persons.
• How a shared device whose only owner has rebuilt gets a new owner without a factory reset.