Both remaining ⚪ protocol rows turned out to be stale.
`AccountKdf.localAccountSalt` is pinned to the published vector and wired into
sign-in for a local relay; `MailboxHoming` and `AccountIdentity.publishHomes`
have shipped the publish and read halves for a while. PARITY.md was describing
a gap that had closed, which is its own kind of wrong — a definition of done
that overstates the work left is one people stop reading.
🔴 What was genuinely missing was on the READING side, and on BOTH clients.
An older home record is GENUINELY SIGNED — the account holder published it,
before they added a second relay. So a relay that wants to be somebody's only
mailbox does not have to forge anything: it serves the record it saw first,
that record verifies perfectly, and the sender delivers to one relay believing
it is delivering to all of them. That is the attack multi-homing exists to
survive, and the serial is what was added to stop it.
The relay refuses a lower serial on WRITE. Nothing refused one on READ:
`verifiedRelays` here and `verifyHomes` on iOS both checked the signature and
stopped. Fixed on both — iOS in ios!116, this is the Kotlin half.
The highest serial seen per address is remembered in the vault and a lower one
is refused. Equal is fine; only strictly lower is a rollback.
🔴 The floor rises only for a record that VERIFIED, via a separate
`verifiedSerial`. Otherwise a hostile relay could hand over an unsigned record
carrying Int.MAX_VALUE, have the client raise its floor to it, and lock out
every later genuine record — turning the rollback defence into a denial of
service against the account holder. Tested.
⚠️ Sealed in the vault and keyed by a hash of the address: which addresses this
device has looked up is exactly the metadata the vault exists to keep off a
stolen phone.
⚠️ The refusal does not claim an attack. A relay that has genuinely fallen
behind serves an old record for honest reasons, and nothing in a client can
tell that from the other case.
8 unit tests. App builds, every JVM suite green.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
