Goal: Build safe cross-chain transfers from Sui to other blockchains, avoiding the usual bridge hacks.

Step 1 — Understand the risk

Problem: Bridges are #1 hack vector in crypto. Why? • Bugs in message verification • Centralized multisigs compromised • Replay attacks

Step 2 — Core design choices

Option A: Lock & Mint • Lock assets on Chain A → Mint wrapped assets on Sui. Option B: Burn & Release • Burn wrapped assets on Sui → Release originals on Chain A.

Step 3 — Implementing on Sui 1. Create a BridgeCap controlled by relayers. 2. Lock assets: • User calls lock(asset, target_chain_addr). • Emit event with proof. 3. Off-chain relayers read event → trigger mint on target chain.

Step 4 — Verification problems

Problem: How to trust off-chain relayers?

Fixes: • Multi-relayer consensus (2-of-3 signatures). • Use light clients (verify other chain headers on Sui). • Time-lock withdrawals to reduce quick exploits.

Step 5 — Replay protection

Problem: Attacker replays the same event → double mint.

Fix: • Store event nonce on-chain. • Reject if already used.

Step 6 — Failure recovery

Problem: Relayer fails mid-bridge.

Solution: • Allow user to cancel after timeout → reclaim locked funds. • Events guarantee funds are not lost.