Bridge Integration

The Lux Bridge uses the MPC network for cross-chain transaction signing. HSM provides the co-signing layer within the MPC nodes.

Architecture

Bridge UI (Next.js)
      │
      ▼
Bridge Server (Node.js)
      │
      ▼ POST /api/v1/generate_mpc_sig
MPC API Server
      │
      ├─► HSM Co-sign (intent attestation)
      │
      ▼
MPC Threshold Signing (CGGMP21/FROST)
      │
      ▼
Destination Chain (broadcast)

How It Works

1. User initiates bridge — selects source/destination chain and amount
2. Bridge server calls the MPC API at POST /api/v1/generate_mpc_sig
3. MPC API receives the request, the HSM signer co-signs the intent
4. MPC nodes execute threshold signing (CGGMP21 for ECDSA, FROST for EdDSA)
5. Signature is returned to the bridge server
6. Bridge server broadcasts the signed transaction to the destination chain

Configuration

The bridge server connects to MPC via:

# K8s
MPC_URL: "http://mpc-api-svc.lux-mpc.svc:8081"
MPC_API_KEY: "<api-key>"

# Local development
MPC_URL: "http://mpc-node-0:8080"

The MPC nodes themselves have HSM configured as described in the MPC Integration guide.

Initiator Key

The bridge server authenticates to the MPC network using an Ed25519 initiator key:

/app/identity/initiator.key  (mounted from K8s secret)

This key is separate from the HSM signer — it proves the bridge server's identity to the MPC network.

Cross-Chain Support

The bridge operates across all Lux chains and selected external networks: