Cross-Chain Bridge
A bridge moves assets between blockchains, usually by locking them on one chain and issuing a representation on another — bridges have been a frequent target of hacks.
Blockchains cannot see each other, so moving a token from one to another needs a bridge. Bridges are useful, but they hold large pools of locked assets and have been among the biggest targets for hackers.
- Category
- Cryptocurrency and Blockchain
- Reading time
- 4 min
- Also called
- Blockchain bridge, Crypto bridge
- Updated
A bridge in plain words
Bridges exist to connect blockchain networks.1
A common design is “lock and mint”: the asset is locked on the original chain and a matching token is created on the other one.1
The minted copy is known as a wrapped asset, and it is only as good as the bridge backing it.2
How a lock-and-mint bridge works
Send to the bridge
Send the asset to the bridge's contract, where it is held.2
Message the other chain
The bridge registers the deposit and signals its counterpart contract.
Receive a wrapped asset
The destination contract creates a wrapped copy of the locked asset.2
Use it on the new chain
Trade or lend the wrapped token like any native asset there.
Burn to return
Burn the wrapped token, and the source contract unlocks the original.2
Assess the security model
Bridges using external validators are usually less secure than natively secured ones.1
Worked examples
Example 1 — Bridge fee cost
$45 in costsHypothetically you bridge 10 ETH at a 0.1% fee plus a $15 network fee, with ETH at $3,000.
| Value sent | 10 × $3,000 = $30,000 |
| Bridge fee | $30,000 × 0.001 = $30 |
| Total cost | $30 + $15 = $45 |
The wrapped ETH you receive is backed by the 10 ETH locked on the source chain.2
Example 2 — Backing shortfall
−4 ETH in backingHypothetically a bridge locks 1,000 ETH backing 1,000 wrapped ETH, and an attacker drains 400 ETH.
| Remaining backing | 1,000 − 400 = 600 ETH |
| Backing per wrapped token | 600 ÷ 1,000 = 0.60 ETH |
| Loss on 10 wrapped | 10 × (1 − 0.60) = 4 ETH |
Bridges often keep a central store of funds backing the bridged assets, and that store is a target.3
Example 3 — Round trip
−$40 for the round tripHypothetically you bridge 5 ETH out and back, paying $20 each way.
| Fees | 2 × $20 = $40 |
| ETH returned | 5 ETH |
On the way back the wrapped token is burned and the original unlocked.2
Trusted vs trustless bridges
| Aspect | Trusted bridge | Trustless bridge |
|---|---|---|
| Who verifies | External operators | The connected chains' validators |
| Extra trust assumption | Yes | No new assumptions |
| Security | Generally lower | Generally higher |
| Main risk | Collusion or key theft | Smart contract bugs |
Where bridges are used
Cheaper fees
Move funds to a chain with lower Trading Fees and Commissions.
Accessing DeFi
Use Liquidity on another network.
Arbitrage
Capture price gaps for the same Trading Pair across chains.
Stablecoin transfers
Move a Stablecoin to where it is needed.
Advantages and disadvantages
Advantages
- Connects otherwise isolated blockchains.
- Opens DeFi and trading on other networks.
- Lets you use cheaper or faster chains.
- Wrapped assets keep price exposure to the original.
Disadvantages
- Bridges are major hacking targets.
- Wrapped tokens depend on the bridge's backing.
- Fees and delays on both chains.
- Complex security models are hard to judge.
Going deeper
Read as far as you need. Each level builds on the one before it.
Common mistakes
Treating wrapped as native
Forgetting a wrapped token depends on the bridge.
Ignoring the trust model
Not checking who verifies transfers.
Using unofficial links
Falling for fake bridge front-ends.
Leaving funds parked
Holding large wrapped balances longer than needed.
Check your understanding
Test yourself before moving on. Each answer comes with an explanation.
Key points to remember
- Bridges move value between blockchains.
- Lock-and-mint creates wrapped tokens.
- Wrapped tokens are only as safe as the bridge.
- Bridges are frequent hack targets.
- Check the trust model before using one.
Frequently asked questions
Is a wrapped token the same as the original?
Why are bridges hacked so often?
Are bridges regulated?
Further learning
- Counterparty Risk
Who you rely on with a bridge.
- Stablecoin
A common asset to bridge.
- Liquidity
Why people bridge to other chains.
- Trading Fees and Commissions
Costs on both chains.
Sources
This article is written in our own words. The sources below support the specific facts, rules and figures marked with a number in the text. Links open the original publisher’s page.
- ethereum.org. Introduction to blockchain bridges (opens in a new tab) Checked .
- Chainalysis. Introduction to Cross-Chain Bridges (opens in a new tab) Checked .
- U.S. Department of the Treasury. Illicit Finance Risk Assessment of Decentralized Finance (2023) (opens in a new tab) Checked .
- Chainalysis. Vulnerabilities in Cross-chain Bridge Protocols Emerge as Top Security Risk (opens in a new tab) Checked .
Educational content, not financial advice. Examples use hypothetical prices and simplified costs; actual fees, margin rules and regulations vary by broker, market and country. We are not affiliated with any publisher linked above. Last reviewed . Report an error or request a source credit.