Trust-Minimized Transfers via Union Bridge (BitVMX)

The Union Bridge is a next-generation bridging protocol that utilizes BitVMX to move assets between Bitcoin and Rootstock with a 1-of-N trust assumption. Unlike traditional federated bridges, Union requires only a single honest functionary to ensure the integrity of the peg.

Prerequisites

• Taproot Wallet: A Bitcoin wallet capable of sending to and receiving from Taproot (P2TR) addresses.
• Rootstock Account: A standard address to receive uBTC (Union BTC).
• Union CLI or SDK: Installed in your development environment.

Getting Started

1. The 1-of-N Security Model

Union uses optimistic verification. When BTC is locked on Bitcoin, a "Challenge-Response" window opens. Functionaries monitor the chain; if an invalid peg-out is attempted, a single honest functionary can trigger a BitVMX fraud proof to stop the transaction.

2. Performing a Peg-In

To move BTC to Rootstock, you must lock funds into a BitVMX-secured VMXO.

1. Request a Deposit Address: The Union API generates a unique Taproot address for your session.
2. Lock Funds: Send your BTC to the generated address.
3. Wait for Confirmations: The bridge requires 6 Bitcoin block confirmations (~60 minutes) to ensure finality before minting uBTC on Rootstock.

3. Performing a Peg-Out

Peg-outs are facilitated by "Operators" who front the BTC to you on the mainchain in exchange for the locked VMXO on the bridge.

// Example: Initiating a Peg-out via the Union SDK
const tx = await unionBridge.initiatePegOut({
  amount: parseUnits("0.05", 8),
  destinationBtcAddress: "bc1p..."
});

Troubleshooting

• Timelock Delays: If a dispute is raised, funds may be locked during the "Chess Clock" dispute period. This is a security feature of BitVMX to allow verifiers to submit fraud proofs.

• Address Compatibility: Ensure you are not sending BTC from a legacy (P2PKH) address to a Taproot deposit address, as some older wallets may fail to calculate the correct witness.

Related Use Cases or Resources

• BitVMX Whitepaper

• Fast Bridging with Flyover

• Institutional Asset Custody