Bridge
A bridge is a system that makes assets or information from one blockchain usable on another. Since blockchains cannot natively see each other, a bridge acts as the connection between them.
How bridges work
The most common design is lock and mint. You send tokens to a bridge contract on the source chain, where they are locked. The bridge then issues an equal amount of a representative token on the destination chain. To go back, the representative token is burned and the original is released.
Other designs use liquidity pools on both chains, swapping your tokens for ones already sitting on the other side, or pass general messages so that apps on different chains can interact. Rollups have official bridges to Ethereum that rely on the rollup's own proof system.
Who verifies the transfer
The key question is who confirms that tokens were really locked on the other chain. Some bridges rely on a small group of validators or a multi-signature wallet; others use light clients or cryptographic proofs. The fewer parties that must be trusted, the harder the bridge is to compromise, but also often the more complex or slower it is.
Why bridges are a major risk
Bridges hold large pools of locked assets, which makes them attractive targets. In February 2022 the Wormhole bridge lost about 120,000 wrapped ETH through a smart-contract bug, and in March 2022 attackers drained the Ronin bridge after gaining control of enough validator keys. If a bridge is drained, the tokens it issued on the other chain can lose their backing.
Bridged tokens also come in competing versions. A token named USDC on a new chain might be the issuer's native version or a bridged copy, and the two are not always interchangeable.
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Frequently asked questions
Are bridges safe to use?
No bridge is risk-free. Safety depends on its verification design, audits, track record and how much trust is placed in a few key holders.
How long does bridging take?
It varies from minutes to days. Withdrawals from optimistic rollups through the official bridge usually wait about a week, while third-party bridges can be faster.
What happens if I bridge to the wrong network?
Funds may arrive at an address you cannot use on that chain, or get stuck. Recovery is sometimes possible with the same keys, but not guaranteed.
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