Cross-chain bridge

Blockchains cannot read each other's state natively, so bridges act as connectors. In the common lock-and-mint model, you deposit tokens into a contract on the source chain and receive a wrapped version on the destination chain; burning the wrapped tokens later releases the originals. Other designs use liquidity pools on both sides, or burn and re-mint tokens issued natively on several chains.

Bridges differ in who verifies transfers: a small group of signers, an external validator network, a light client or a zero-knowledge proof. The fewer and more centralized the verifiers, the more trust users must place in them.

Because they hold large pools of locked assets, bridges are prime targets. The Ronin bridge lost more than $600 million in 2022 after attackers obtained validator keys, and Wormhole and Nomad were also drained that year.