What is a crypto bridge, and is it safe?

Blockchains can't see each other. Ethereum doesn't know what happens on Base, and Base doesn't know what happens on Arbitrum. A bridge is the service that moves value between them. It is useful, and it is also where some of crypto's largest thefts have happened.

The three ways bridges work

1. Lock and mint

You lock your tokens in a contract on the first network, and the bridge creates (“mints”) a matching wrapped token on the second. The wrapped token is only worth something as long as the locked originals are safe. USDbC on Base is an example.

2. Burn and mint by the issuer

Some token issuers run their own crossing. Circle, which issues USDC, can destroy (“burn”) USDC on one network and create new, native USDC on another. You end up with the real token on both sides, not a wrapped copy.

3. Liquidity networks

A provider who already holds tokens on the destination network pays you there, usually within minutes, and collects your tokens on the source network. Nothing new is minted. You are relying on the provider's system to settle correctly.

Why bridges get hacked

A bridge that locks tokens ends up holding a large pile of them in one place, which makes it a target. In 2022 alone, the Ronin bridge lost about $625 million, Wormhole about $320 million and Nomad about $190 million. The causes were stolen keys, a bug in how messages were verified, and a faulty software upgrade.

How to bridge more safely

• Prefer native tokens. Receiving native USDC is safer than holding a wrapped copy that depends on a bridge staying solvent.
• Don't park funds in wrapped tokens longer than you need to.
• Use established routes, and check what you will receive and on which network before you sign.
• Send a small test amount first for large moves or unfamiliar routes.
• Type the site address yourself. Fake bridge sites are a common trap, especially through search ads and links in messages.

How the swap page handles it

When you pick a different destination network on the swap page, the swap and the bridge are handled in one flow by CoW Protocol and the bridge providers it works with. The quote shows the bridge details and the amount you will receive before you sign, and your tokens go from your wallet straight into that flow. This site never holds them.

Nothing here is financial advice. Crypto transactions cannot be reversed.