How bridges work
Three main architectures:
- Lock-and-mint — source-chain tokens are locked in a bridge contract; equivalent wrapped tokens are minted on the destination chain. Burning the wrapped version unlocks the originals. WBTC on Ethereum (wrapping Bitcoin) is the most well-known example.
- Liquidity-network — a bridge maintains pools of assets on both chains; a swap on one side pays out from the pool on the other. Across and Stargate use this model.
- Canonical rollup bridge — Ethereum L2s have official bridges (Arbitrum, Optimism, Base) where withdrawals are cryptographically anchored to L1. Deposits are fast (minutes); withdrawals take 7 days (for optimistic rollups) because of the fraud-proof window.
Validators or multisigs usually sign off on lock-and-mint bridges — which is exactly where most bridge exploits have targeted. Compromise the signers, drain the locked collateral, the wrapped tokens become worthless.
Major bridge exploits
A short list of the ones that shaped the industry:
- Ronin (2022) — $625M drained; 5 of 9 validators compromised.
- Wormhole (2022) — $320M exploit via a signature-verification bug; Jump Crypto covered the loss.
- Nomad (2022) — $190M via a flawed initialization; anyone could copy an earlier valid message and drain the contract.
- Multichain (2023) — ~$200M “exit” by the team; collateral locked in contracts no one can unlock.
- Orbit Bridge (2024) — $80M exploit via signature verification.
The pattern repeats: complex cryptography + multisig trust assumptions + billions in locked collateral = a target with a huge payoff and often a single point of failure.
Risks and considerations
Bridges remain crypto’s weakest link. Before using one:
- Check the bridge’s security model — canonical rollup bridges are structurally safer than third-party multisigs.
- Look at TVL and age — bridges with $100M+ TVL running for years without incident (Across, Connext, LayerZero’s canonical deployments) are better bets than new entrants.
- Minimize the amount bridged — only move what you need for the specific operation. Don’t park long-term capital on a destination chain unless you need to.
- Prefer native-asset bridges where available — USDC on Arbitrum has a native Circle-issued version, not just a wrapped one. This eliminates bridge risk for that specific asset.
- Avoid wrapped versions of wrapped versions — a BTC → wBTC → wwBTC path inherits the risk of both bridges.
For active traders, the fastest stablecoin bridges (Across, Stargate, Hop) move USDC between rollups in 2-5 minutes for 5-10 bps. For retail moving $50, gas cost often exceeds the bridge fee — batch the move with other activity to amortize the cost.