Audit checklist item C-3 ("the highest-value check here") is no longer
UNVERIFIED. It failed, and the failure is a live F-03 instance rather than a
theoretical one.
Three distinct fleet nodes — archipelago-1, archy-x250-beta and archipelago —
present byte-identical ECDSA, ED25519 and RSA host key fingerprints. Two of
them (archipelago-1, archy-x250-beta) also present the same TLS certificate,
so they share the TLS private key as well.
Gathered read-only and remotely: ssh-keyscan plus an anonymous TLS handshake.
No node was logged into, nothing was written, nothing was rotated. A weaker
instrument than the checklist's on-node commands, chosen because it needs no
access and therefore covers the reachable fleet rather than two nodes — and it
is sufficient for the FAIL condition, which is any fingerprint appearing twice.
Ruled out the obvious alternative (one machine registered three times on the
tailnet): all three answered live TCP within the same minute, and tailscale
ping resolves them to different physical endpoints on different continents
under different tailnet accounts.
One finding worth more than the count: `archipelago` has a UNIQUE TLS cert
(CN=austin-sapien) and SHARED SSH host keys, because it was renamed and
server.set-name re-mints the cert via regenerate_tls_cert() while touching
nothing else. So TLS uniqueness is not evidence that a node's key material is
per-node — any renamed node gets a unique certificate for free. Checked on TLS
alone, that node would have looked clean. Recorded because it justifies the
audit script reporting the two key classes separately instead of issuing one
node-level verdict.
All three are listed under "shared verdict, deliberately not rotated" with the
reason and the next step. A verification task that remediates is a
verification task that takes a node offline.
Also records what this does NOT establish, each with the evidence still
needed: same-ISO provenance, the script's own verdict on those nodes, that a
rotation preserves the operator's live session on real hardware, that
host_secrets reaches system.stats on a real node, and the four nodes that were
unreachable at scan time.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
