Cross-Chain Bridges
Cross-chain bridges enable asset and message transfer between independent blockchains by locking assets on the source chain and minting representations on the destination — with trust models ranging from multisig committees (trusted) to light client verification (trustless) to optimistic verification with fraud proofs.
Bridges solve blockchain isolation — assets and data on Ethereum can't natively move to Polygon, Arbitrum, or Solana. The lock-and-mint pattern dominates: lock ETH on Ethereum, mint wrapped ETH on the destination chain. When bridging back, burn the wrapped token and unlock the original. Bridge security varies dramatically: trusted bridges use multisig committees (fast but trust-dependent), optimistic bridges assume messages are valid unless challenged with fraud proofs (delayed withdrawal), and trustless bridges verify source chain state via light clients or ZK proofs (strongest security, highest cost). Bridges are the most attacked DeFi primitive — over $2.5B stolen in bridge hacks (Ronin $625M, Wormhole $326M, Nomad $190M). The fundamental challenge: verifying one chain's state on another chain without trusting an intermediary.
Tradeoffs
Strengths
- Enable the multi-chain ecosystem by connecting isolated blockchains
- Liquidity network bridges provide fast, native-asset transfers
- ZK bridges offer trustless verification with strong cryptographic guarantees
- Native rollup bridges inherit L1 security
Weaknesses
- Bridges are the most hacked DeFi primitive ($2.5B+ stolen)
- Multisig bridges concentrate trust in a small group of signers
- Wrapped assets introduce counterparty risk (bridge insolvency = worthless tokens)
- Bridge latency (hours to days for high-security bridges) degrades user experience
Likely Follow-Up Questions
- Why are bridges the most attacked primitive in DeFi?
- How does IBC achieve trustless cross-chain communication?
- Compare the security models of multisig, optimistic, and ZK bridges.
- What is the interoperability trilemma and how do different bridges address it?
- How do liquidity network bridges differ from lock-and-mint bridges?
- What defense mechanisms could have prevented the Ronin bridge hack?
Source: editorial — Synthesized from bridge postmortems, IBC specification, LayerZero and Wormhole documentation, and Li.Fi bridge aggregation research