How Does a Blockchain Bridge Work?

A blockchain bridge is a system that moves crypto assets or data from one blockchain to another. Separate networks can’t read each other’s records directly, so if you want to use ETH from Ethereum on a Layer 2 or another chain, you need a bridge. It locks or burns the asset on the source chain and creates or releases its counterpart on the destination chain.

Bridges make cross-chain activity possible, but some of the biggest hacks in crypto history have targeted them. That’s why it pays to know which bridge you’re using and how it works.

Why doesn’t switching networks in your wallet move your balance?

On EVM-compatible networks, your wallet shows the same address everywhere, but each network keeps its own separate ledger. Switching your wallet from Ethereum to Arbitrum doesn’t move anything; it only changes which ledger you’re looking at. For 1 ETH on Ethereum to show up on Arbitrum, an on-chain bridge transaction has to happen.

How do bridges work?

• Lock and mint: the asset is locked in a bridge contract on the source chain, and the same amount of a wrapped token is minted on the destination. On the way back, the wrapped token is burned and the original released.
• Burn and mint: for tokens controlled by their issuer, the asset is burned on the source chain and freshly minted on the destination. Circle’s CCTP for USDC works this way, producing native, Circle-issued USDC on the destination chain.
• Liquidity networks: the bridge holds token pools on both chains. You deposit into the pool on the source chain and get paid out of the pool on the destination. It’s fast, but depends on the pool having enough liquidity.

Official rollup bridges, such as Arbitrum’s or Base’s own, rely largely on Ethereum and the rollup’s proof system for security. Third-party bridges like Across, Stargate and Wormhole rely on their own validators, oracles or liquidity providers.

Native vs bridged tokens

The token a bridge creates on the destination chain isn’t necessarily the same as the issuer’s native token there. A network might have both Circle’s native stablecoin USDC and an older bridged version labeled something like “USDC.e.” They share a name but have different contract addresses.

That matters in practice: an exchange may only accept the native version for deposits, and a DeFi app may only support the other. A bridged token’s value also depends on the security of the bridge behind it; if the bridge is hacked, the wrapped token can end up unbacked.

Bridge or exchange withdrawal?

Many centralized exchanges let you withdraw directly to Layer 2s and other networks. Depositing to an exchange and withdrawing on the network you want can be cheaper and simpler than bridging, but the exchange takes custody of your funds in the meantime. Bridging keeps the assets in your own wallet, at the cost of taking on the bridge contract’s risk. Either way, choosing the right network is the ground rule.

How to use a bridge, step by step

1. Pick the bridge: where possible, use the destination network’s official bridge or the method the token issuer recommends. Get the address from a bookmark or official docs.
2. Set the source and destination: connect your wallet on the source network, then choose the destination network and token.
3. Check the recipient: most bridges default to your own address. If you enter a different one, make sure you control it on the destination network.
4. Work out the total cost: add up source-chain gas, the bridge fee and the net amount that will arrive.
5. Have gas on the destination: networks like Arbitrum and Base need ETH. Some bridges offer to send a little gas token along automatically.
6. Track it: save the source transaction’s TXID and check arrival on the bridge’s status page or the destination chain’s block explorer.

How long does a bridge transfer take?

It varies widely by bridge type and direction. Depositing from Ethereum to a rollup through the official bridge usually takes minutes. Withdrawing from an optimistic rollup back to Ethereum through its official bridge takes around seven days because of the challenge period.

Fast bridges built on liquidity networks cut that wait to minutes by paying you from their own pools on the destination chain. They charge an extra fee, and you take on that bridge’s contract risk. If a transfer is taking a while, confirm the source transaction first, then check the bridge’s status page, and don’t send the same transfer again.

Are blockchain bridges safe?

Because bridges hold large pools of locked assets, they’re a prime target. In 2022, attacks on the Ronin, Wormhole and Nomad bridges led to hundreds of millions of dollars in stolen funds. Some of those incidents stemmed from compromised validator keys, others from smart contract bugs.

To reduce your risk:

• Favor bridges that have operated for a long time, have been audited and clearly document their security model.
• Rather than holding large amounts of bridged tokens long-term, switch to the issuer’s native version where possible.
• Send a small test amount the first time you use a bridge.
• Watch out for fake bridge sites and for “support” accounts claiming your transfer is stuck and asking for your recovery phrase.

Frequently asked questions

My bridged token isn’t showing up on the destination chain. What should I do?

First check the bridge’s status page to see whether the transfer has completed. If it has, make sure your wallet is set to the destination network, and if the token still doesn’t appear, add it manually using its contract address. Whether you received the native or bridged version determines which contract address to add.

How is Bitcoin bridged to other chains?

On smart contract networks like Ethereum, bitcoin is usually represented by wrapped tokens such as WBTC. The BTC backing them is held by a custodian or bridge structure, so wrapped BTC depends on that structure’s security in a way that native BTC does not.

Sources

• Ethereum: cross-network bridges
• Circle: cross-chain USDC transfer
• Arbitrum: network and bridge documentation