Cross-chain bridge

A bridge does not move tokens from one chain to another: it acts as a messaging layer. The dominant model is lock-and-mint. The user locks the native asset in a custody contract on the origin chain and the bridge mints an equivalent wrapped token on the destination, such as WBTC or whETH. To return, the wrapped token is burned on the destination and the original is released. The critical invariant is that every wrapped token in circulation stays fully backed by what is locked.

What sets one bridge apart from another is who verifies the origin event. Some bridges rely on a federation or multisig of validators that attest the event, some use a light client that cryptographically verifies the origin's consensus proofs, optimistic bridges assume validity unless a fraud proof is filed, and liquidity networks use pools on both sides without minting. The marketing label trust-minimized matters less than the concrete question of who validates.

It is the practical piece of interoperability: moving stablecoins or ETH to a cheaper L2, connecting appchains, or bringing BTC into Ethereum DeFi. It also concentrates value, so verification design and key custody are decisive. The sector's track record leaves verifiable engineering lessons: Ronin (Sky Mavis) suffered a compromise of 5 of 9 validator keys in March 2022; Wormhole had its guardian signatures forged in February 2022; Nomad had a contract initialization flaw in August 2022. The design takeaway is clear: for tokenized RWA, compliance control (ERC-3643, KYC) must travel with the asset, not just its value.