How Bridges Work

At a high level, every token bridge solves the same problem: Chain B must believe something true happened on Chain A before it moves value. The differences lie in who attests to that truth — smart contracts, validator sets, relayers, or light clients — and what happens if they lie.

Relayers are off-chain actors that watch events and submit proofs. Validator sets — often multisigs or proof-of-stake committees — vote on whether a transfer is valid. Some designs run optimistic verification with a challenge window; others use zero-knowledge proofs tied to L1 state.

Speed and cost vary with the verification model. A small multisig can confirm in seconds; a trustless light client may cost more gas and take longer. Bridges are engineering compromises, not magic portals.