serveReveal returning an error aborted startup, so a new capability could stop a ring from doing the thing it already existed to do. Signing was working before openings were possible and should keep working when one is not. Nothing is hidden by carrying on. The failure is logged here, and an opening that goes short already reports how many answered out of how many it needed — which is the number that matters and the place someone is looking when it does.
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.