zeekay
5ae17289d2
Red round 5 finding B1. The embedded dispatcher on --threshold-listen
was an anonymous local signing oracle:
1. Any process on the host could POST `{"method":"frost.sign",...}`
and obtain signatures with no auth gate (only the API on :9800
enforced MPC_INTERNAL_API_KEY).
2. An operator typo `MPC_THRESHOLD_LISTEN=0.0.0.0:7300` exposed it
cluster-wide.
3. Any SSRF inside mpcd pivoted into the dispatcher.
Fix mirrors the existing internal-API auth pattern (cmd/mpcd/main.go
line ~456):
- Auth token: read MPC_THRESHOLD_AUTH_TOKEN; if unset, derive a
deterministic per-cluster token from the node Ed25519 seed
(SHA-256(seed || "mpc-threshold-rpc") hex). All nodes share the
same key without extra config; log warns when derivation is used.
Server.SetAuthToken installs the gate.
- Loopback bind: refuse non-loopback addr unless
MPC_THRESHOLD_ALLOW_REMOTE=1 — operators must explicitly
acknowledge the exposure. Bare `:port` (= 0.0.0.0) is NOT loopback.
Also picks up luxfi/threshold v1.6.10 which removes the pulsar/corona
in-memory-token surface (Red HIGH B2) — pulsar.*/corona.* now return a
typed "not yet implemented" error.
Tests:
- TestIsThresholdLoopback locks the loopback predicate (8 cases:
127.0.0.1, [::1], localhost OK; 0.0.0.0, :port, RFC1918 refused).
- TestEmbeddedDispatcher_AuthGate proves 401 on missing/wrong token,
200 on valid token through the dispatcher mpcd installs.
4 tests pass in cmd/mpcd (was 2, +2).
mpcd — MPC Daemon
mpcd is a threshold-signature daemon. It speaks ZAP wire protocol over
TLS 1.3 directly between peers — no NATS, no Consul, no PostgreSQL in the
critical path. The daemon is the same binary in every deployment shape;
the operating mode is selected entirely by flags.
Operating modes
There is exactly one start command (mpcd start) and the topology is
determined by the --peer and --threshold flags:
| Topology | Flags | Use |
|---|---|---|
| Standalone (1-of-1 self-loop) | --threshold 1 (no --peer) |
Smoke tests, dev sandbox |
| Networked t-of-n cluster | --threshold t --peer ... (n−1 peers) |
Production |
In all cases mpcd runs the consensus-embedded transport
(pkg/transport). The "consensus" here is local PoA membership over the
node's own Ed25519 identities — it is intentionally not the Lux mainnet
chain, because key shares must never leave the cluster.
Standalone (1-of-1)
mpcd start \
--node-id solo \
--listen :9999 \
--api :9800 \
--data /var/lib/mpcd \
--threshold 1
Starts mpcd with itself as the only quorum member. /healthz will report
signing_quorum: true immediately. Keygen and signing of fresh wallets
require ≥2 parties — CGGMP21 and FROST cannot produce shares with a
single party — so this mode exists only for boot-up smoke tests, e2e
harness fixtures, and verifying TLS / membership / API plumbing. For real
signing, run a multi-node cluster.
Networked (t-of-n)
# Node 0
mpcd start --node-id node0 --listen :9999 --api :9800 \
--data /data/node0 --threshold 2 \
--peer [email protected]:9999 --peer [email protected]:9999
# Node 1
mpcd start --node-id node1 --listen :9999 --api :9800 \
--data /data/node1 --threshold 2 \
--peer [email protected]:9999 --peer [email protected]:9999
# Node 2 — same pattern
The daemon expects the cluster size n = len(peers) + 1 and rejects start
when threshold > n. See pkg/transport/registry.go::HasSigningQuorum for
the quorum arithmetic.
Smoke test
go test -tags=integration ./cmd/mpcd/... -count=1 -timeout 90s
standalone_test.go builds mpcd, runs it with --threshold 1 on free
ports and a fresh data directory, polls /healthz until quorum holds,
and asserts the response shape. It does not exercise keygen — see e2e/
for that.