How Crypto Bridges Work, and How to Use Them Carefully

Blockchains don’t natively talk to each other. A token on one chain can’t simply be sent to an address on another. A bridge is a protocol that makes it look like you moved tokens between chains. Bridges are useful, but they’ve also been behind some of the largest hacks in crypto history, so they’re worth understanding before you use one.

This guide is educational and does not recommend any specific bridge.

Why people use bridges

• To use an app or layer 2 network with lower fees.
• To move a stablecoin or other token to a chain where they want to use it.
• To consolidate funds onto one network.

If you only want to move funds from an exchange to a wallet on a particular network, you often don’t need a bridge at all. Many exchanges let you withdraw directly on several networks. See How to Send Crypto Safely.

Main bridge designs

Lock and mint

1. You send Token A to the bridge’s contract on Chain 1, where it’s locked.
2. The bridge mints a “wrapped” version of Token A on Chain 2.
3. To go back, you burn the wrapped token on Chain 2 and the original is unlocked on Chain 1.

The wrapped token is only as good as the bridge holding the originals. If the locked funds are stolen, the wrapped tokens may lose their backing.

Burn and mint (native)

Some token issuers run their own system that burns tokens on one chain and mints the same native token on another. There’s no separate wrapped version, but you rely on the issuer’s system working correctly.

Liquidity networks

The bridge holds pools of tokens on each chain. You deposit on Chain 1 and receive tokens from the pool on Chain 2. These can be fast, but depend on pool liquidity and the security of the contracts and whoever verifies transfers.

Rollup “canonical” bridges

Layer 2 networks usually have an official bridge to and from Ethereum. Withdrawals from some types of rollup back to Ethereum can take about a week by design, because of how they’re verified. Third-party bridges may offer faster exits for a fee and extra risk.

Why bridges get hacked

Bridges often hold large amounts of locked funds and depend on complex code and sets of validators or signers. Attackers have exploited:

• Smart contract bugs.
• Compromised validator or multisig keys. Several high-profile hacks came from attackers gaining control of enough signing keys.
• Faulty verification logic that accepted fake deposit messages.

Billions of dollars have been lost to bridge exploits over the years. That’s not a reason to never use one, but it is a reason to limit how much you hold in bridged assets and for how long.

Risks to you as a user

1. Bridge exploit draining locked funds behind your wrapped tokens.
2. Fake bridge sites that look identical to real ones but drain your wallet. See phishing.
3. Wrong token. Several wrapped versions of the same asset can exist on one chain and may not be interchangeable.
4. Stuck transfers if a bridge pauses or a chain has problems.
5. Unlimited token approvals left behind after you bridge.
6. Fees on both sides, including gas on each chain and a bridge fee.

Safety checklist before you bridge

1. Ask if you need to bridge at all. A direct exchange withdrawal on the target network may be simpler.
2. Get the bridge’s address from an official source, such as the network’s or token issuer’s documentation. Bookmark it. Don’t click ads or links in DMs.
3. Check what you’ll receive. Native token or wrapped version? Which contract address? Is it the version apps on that chain actually use?
4. Check you’ll have gas on the destination chain. Otherwise your tokens may arrive but you can’t move them.
5. Read the time estimate. Some routes take minutes; some take days.
6. Send a small test first.
7. Review the approval. Approve only the amount you’re bridging if the interface allows it.
8. Keep the transaction hashes from both chains until the transfer completes.
9. Revoke approvals afterward. See How to Review and Revoke Token Approvals.
10. Don’t leave large balances in bridged assets longer than you need to.

Step-by-step: a typical bridge transfer

1. Open the official bridge site from your bookmark.
2. Connect your wallet. Check the site’s address in your browser bar.
3. Choose source chain, destination chain and token.
4. Enter a small test amount and review the fees and estimated time.
5. Approve the token (one transaction) and confirm the bridge transfer (another).
6. Wait. Track progress in the bridge interface or on block explorers.
7. Check the token arrived in your wallet on the destination chain. You may need to add the token’s contract address to see it.
8. Repeat with the full amount.

Taxes (US, general)

Whether moving tokens through a bridge is a taxable event is not settled for every case. Receiving a different wrapped token could be viewed as an exchange. Keep detailed records and consult a tax professional.

Common mistakes

• Using a fake bridge from a search ad or DM.
• Arriving with no gas on the destination chain.
• Receiving an unsupported wrapped token.
• Bridging large amounts without a test.
• Leaving unlimited approvals in place.
• Panicking during normal delays and falling for “support” scammers who promise to speed it up.

Key takeaways

• Bridges let tokens appear to move between chains, usually by locking and minting or using liquidity pools.
• They’ve been frequent hacking targets, so limit exposure.
• Use official links, check what token you’ll receive, test small and revoke approvals afterward.