Cross Chain Bridge

When to activate

• Building token bridges between EVM chains
• Implementing cross-chain messaging protocols
• Designing wrapped asset mechanisms (wrapped ETH on Polygon, etc.)
• Integrating existing bridges (LayerZero, Wormhole, Axelar)
• Building cross-chain NFT bridges

When NOT to use

• For single-chain applications
• For centralized exchange transfers
• For off-chain cross-database synchronization

Instructions

1. Choose bridge pattern. Lock-and-mint (canonical), liquidity network (fast), or message-passing (general).
2. Select verification. Validators (centralized), optimistic (fraud proofs), or light client (trustless but expensive).
3. Implement lock side. Deposit contract, event emission, nonce tracking, replay protection.
4. Implement mint side. Verification of source chain event, mint/claim function, replay protection.
5. Handle edge cases. Source chain reorgs, validator downtime, stuck transactions, partial fills.
6. Security. Multi-sig for validators, rate limiting, maximum bridge amounts, emergency pause.
7. Testing. Simulate both chains with Foundry. Test reorg scenarios, validator failures, concurrent bridges.

Example

Lock-and-Mint Bridge Flow:

Source Chain (Ethereum):
1. User deposits 1 ETH to Bridge contract
2. Bridge emits LockedEvent(user, amount, destinationChain, nonce)
3. Relayer picks up event

Destination Chain (Polygon):
4. Relayer submits proof of LockedEvent
5. Verifier confirms event authenticity (validator signatures)
6. Bridge mints 1 WETH on Polygon to user
7. User can redeem WETH back to ETH via reverse flow