What Is Bridge?

Blockchains cannot directly read each other's state, so intermediary mechanisms are needed to move assets. The most common method is the “lock and mint” model: the user locks their token on the source chain in the bridge's smart contract, and a wrapped token representing that asset is minted on the destination chain. On the way back, the wrapped token is burned and the original asset is released. Some bridges instead swap through liquidity pools that sit ready on both chains.

Bridges let users take advantage of lower fees or applications on different networks; official bridges are also used to move to layer 2 networks. The trust model varies from bridge to bridge: some rely on a small group of validators or a multisig, while others rely on light clients or cryptographic proofs.

Because they hold large amounts of locked assets, bridges have been the target of some of the biggest attacks in cryptocurrency history; in 2022, hundreds of millions of dollars in assets were stolen from the Ronin and Wormhole bridges. Smart contract bugs, compromised validator keys and wrapped tokens left without backing are the main risks, which is why a bridge's security model and audit history matter.