Until now any member could change a group's roster or name. Groups now
have admins, and every change to membership, roles or the name is an
operation signed by an admin's identity key (XEdDSA). Recipients verify
the signature against the admin's key from their own contacts, never a
key carried in the same message; the relay plays no part.
- Operations form a hash chain with an epoch; gaps or forks are held back
and resolved by a signed state from an admin.
- Groups created by older versions migrate with the creator as admin; if
the creator has left, the smallest fingerprint takes over
deterministically on every device.
- Mixed groups with older clients keep working in a compatibility mode
until every member advertises admin support; that capability can only
be added, never withdrawn.
- The last admin cannot step down or be removed.
The verification rules live in a network-free policy module with its own
tests.
Julius Joska
9a638545dd