Linea Bridge: How to Move Assets Between Ethereum and Linea

The Linea Bridge is an official tool for moving ETH and ERC-20 tokens from the Ethereum mainnet to the Layer 2 zkEVM network called Linea. It allows deposits from Ethereum to Linea and withdrawals from Linea to Ethereum, but in different ways and with various timing.

What Linea Is

Linea is a Layer 2 (type 2) network, which is zkEVM. In other words, it is an Ethereum Virtual Machine implementation with zero-knowledge proof processing transactions. The transactions are processed off-chain on the Linea network and submitted to Ethereum for validity proof verification in a compressed form.

The "EVM-compatible" feature implies that Ethereum smart contracts, wallets, and development tools work on Linea out of the box or with minimal changes. An Ethereum smart contract can be deployed on Linea similarly, and Linea DApp interactions happen with the same wallet addresses that are used on Ethereum.

The Linea gas token is ETH. There is no separate Linea chain-specific gas token. Users pay fees in ETH on Linea and Ethereum.

How the Linea Bridge Works

The Linea Bridge works on the basis of the canonical bridge architecture, which means that the Linea Bridge is not just a third-party liquidity bridge but an integral part of the Linea protocol. The zero-knowledge proof system that secures the Linea protocol ensures better security than the one required by an external third-party liquidity bridge.

The process of deposit from Ethereum to Linea works by locking the tokens on the Ethereum side (in the canonical bridge contract). The Linea network notices the action and mints a corresponding representation of the asset. The native Linea ETH and an ERC-20 token are bridged as their respective equivalents.

Withdrawals from Linea to Ethereum require a more complex procedure. The Linea network generates a zero-knowledge proof covering the batch of transactions that includes the withdrawal transaction. This proof is verified on Ethereum and then assets are released from the Linea bridge contract on the Ethereum side. This proof generation and verification stage is the reason why withdrawals from the zkEVM network take more time than deposits.

The Official Linea Bridge Interface

The official Linea Bridge interface is located at bridge.linea.build and it is run by Consensys, the creator of MetaMask and Infura. This is the canonical bridge for Linea and a starting point recommended in Linea documentation. Third-party bridges also support the route between Ethereum and Linea, but the official bridge is more connected to Linea protocol's security.

The interface supports MetaMask directly because of Consensys' ownership of this product. Other EVM-compatible wallets can be used via WalletConnect or direct injection. To use the Linea Bridge, Linea should be added to your wallet. Network parameters: chain ID 59144, RPC URL https://rpc.linea.build, currency symbol ETH. The information can be added via Chainlist or directly in MetaMask's network settings.

Depositing from Ethereum to Linea

Deposits are performed faster than withdrawals because of the absence of the proof generation process. Upon the lock transaction on Ethereum, the Linea sequencer detects the transaction and credits the Linea account usually within a few minutes to twenty minutes, depending on the Ethereum block times and processing queue of the sequencer.

Step 1: Connect Your Wallet

Go to bridge.linea.build and connect your wallet. Make sure that the network selected in your wallet is Ethereum mainnet.

Step 2: Select the Asset and the Amount

Select ETH or one of the ERC-20 tokens from the asset list. If your ERC-20 token is not in the list, enter the contract address manually. The amount of tokens to deposit is shown, as well as the amount of tokens that you are going to receive after the fee deduction.

Step 3: Approve and Bridge

For ERC-20 tokens, you will first need to authorize the bridge contract to spend the tokens on your behalf. It is done only once for each token. Then click "Bridge". The gas fee on Ethereum is shown in the interface prior to the transaction approval.

Step 4: Verify the Receipt on Linea

Connect the Linea network to your wallet and verify the receipt of the deposited tokens. In case your ERC-20 token is not shown automatically, add it using the contract address on Linea. Lineascan (lineascan.build) is a Linea explorer and it shows the token balances on Linea.

Withdrawing from Linea to Ethereum

Withdrawing tokens from Linea requires a longer process. The Linea protocol generates a zero-knowledge proof that covers the transaction batch including your withdrawal and sends it to Ethereum.

There are three stages of the process: the withdrawal transaction submission on Linea, generation of the proof by the prover, verification of the proof by the verifier contract on Ethereum and release of the assets from the canonical bridge contract.

The withdrawing process requires two transactions on the Ethereum side: one to claim the withdrawal, and sometimes a separate claiming transaction. The bridge interface shows the status of the withdrawal process and lets you know when it is time to claim your assets.

Withdrawal Time

Linea claims a target proof generation and finalization time of several hours to over a day for canonical bridge withdrawals. The exact withdrawal time depends on network activity and proof generation pipeline of Linea. This is not a bug but the required time of the proof generation process. Those who require quick exit from Linea to Ethereum can use third-party liquidity bridges that are explained below.

Fees When Using the Linea Bridge

Ethereum Gas Fees

Both deposits and withdrawals require Ethereum transactions, and the cost of the transaction is measured in ETH gas. In case of deposits, the cost of the transaction is the gas for the lock transaction on the Ethereum side. In case of withdrawals, the additional gas fee for the claiming transaction is required on Ethereum. The Ethereum gas fee varies with network congestion and ranges from a few dollars up to much more during busy times.

Linea Gas Fees

All transactions on Linea are paid in ETH but at lower rates in comparison with Ethereum. The lower rates are the main benefit of using the Layer 2 - the same ETH gas token is used, but the cost of each transaction is much lower. Linea's fee structure includes the execution fee for processing the transaction on Linea and the data availability fee for posting compressed data on Ethereum.

Bridge Protocol Fee

The canonical Linea Bridge does not charge any additional protocol fee beyond the gas fees paid on each side. The total cost you pay is the cost of transactions that you perform on Ethereum and Linea. In case of third-party bridges supporting the Ethereum-Linea route, they charge an additional fee for the speed or liquidity they provide.

Third-Party Bridges for Faster Transfer

There are some third-party bridges that provide the Ethereum-Linea route and allow performing a transfer faster than the canonical bridge, especially for withdrawals. Such bridges use liquidity pools where a liquidity provider on the Ethereum side releases the tokens immediately, and the bridge settles the cross-chain transfer in the background.

Across Protocol, Stargate, and Jumper Exchange (which aggregates several bridges) all support the Linea route and allow completing the transfer in a few minutes instead of a few hours. The drawback is the fee charged by the liquidity provider and the different security model - you are trusting the third-party protocol smart contracts and liquidity instead of the canonical bridge proof system.

In case of small transfers where the canonical bridge withdrawal time is a practical problem, the third-party bridges are acceptable. But for large transfers where security is the primary concern, the canonical bridge provides better guarantees because of its direct connection to the security of the Linea protocol.

What the zkEVM Architecture Means for Bridge Security

ZK in zkEVM stands for zero-knowledge - it is a cryptographic technique where a party can prove that a statement is true without disclosing the data. In the case of Linea, the prover generates a zero-knowledge proof that the batch of transactions was executed correctly according to Ethereum rules without posting the whole data of each transaction on Ethereum.

The zero-knowledge proof is checked by the verifier contract on Ethereum. If the proof is valid, Ethereum accepts the transaction batch as correct and processes the state changes. Otherwise, the proof is rejected and no state change happens. Thus, it is mathematically difficult to submit an incorrect state on Ethereum, which is the reason why zkEVM bridges have a better security model than bridges that rely on fraud proofs or external validators.

The practical conclusion for the users of the canonical Linea Bridge is that it inherits this security feature. The withdrawal that has been finalized through zero-knowledge proof verification on Ethereum is proven cryptographically, not by the reputation or economic incentives of a third party.

Supported Assets

The canonical Linea Bridge has native support for ETH and a list of ERC-20 tokens selected by Consensys. All other ERC-20 tokens can be bridged manually with the help of the contract address but the bridged token on Linea will be a newly wrapped token.

Tokens that are officially listed by Linea or the token issuer are preferable for DeFi activities on Linea, because the Linea decentralized exchanges and other protocols are configured in a way to use the canonical bridged versions of the most popular tokens. Bridging the manually added token instead of the officially listed token can cause compatibility problems with some protocols.

In case of stablecoins, some token issuers deployed the native version of the token on the Linea network rather than using the bridge. For example, USDC from Circle may have a native version of the token issued on Linea by Circle itself, not the bridge-wrapped one from Ethereum. Using the native version of the token is preferable because it does not depend on the bridge contract.

Risks to Consider Before Bridging

Smart Contract Risk

The canonical bridge contracts on both sides have been audited, but no smart contract can be considered risk-free. Any vulnerability in the bridge smart contract may allow an attacker to access the locked funds. Consensys has published the audit report of the core contracts of Linea and it is available on the Linea documentation website.

Withdrawal Delay

Withdrawal delay of the canonical bridge is the known characteristic of the bridge, not a bug, but this is a practical constraint. If you need quick access to funds on Ethereum, plan for the withdrawal time or use a third-party bridge. Bridging to Linea and expecting quick access back to Ethereum may lead to a misunderstanding about the canonical bridge.

Sequencer Centralization

Linea is now using the centralized sequencer run by Consensys. The sequencer orders transactions and batches them for zero-knowledge proof generation. If the sequencer goes down, transaction processing is paused. Consensys promised decentralization of the sequencer in the future, but as of now, it is a single point of operation dependency. This does not affect the funds' security because the zero-knowledge proofs still make impossible to deceive Ethereum but affects the liveness of the system.

Phishing and Unofficial Bridges

As with any bridge, the fake interface that mimics the official one is a risk. Never go to the bridge via links from social media or community channels. Always check the URL carefully before connecting your wallet or signing any transactions.

DeFi ecosystem of Linea and the Reasons to Bridge

There are various decentralized finance protocols on Linea, such as decentralized exchanges, lending platforms, and yield protocols. Some of them are Lynex and Nile Exchange. Several bigger protocols also deployed versions of their products on Linea. The bridge is the gateway to all this activity - without it, there is no way to bridge the tokens from Ethereum to the Linea DeFi ecosystem.

The liquidity on Linea is smaller for most assets in comparison with Ethereum mainnet. That is why large trades on Linea may have slippage. It is a normal characteristic of the growing layer 2 ecosystem. With the growth of the liquidity bridged from Ethereum and the deployment of new protocols, the liquidity improves. Verification of the liquidity on Linea DEXes before bridging helps set realistic expectations for swap efficiency.

Common Mistakes When Using the Linea Bridge

Not leaving some ETH for gas is the most frequent mistake. The canonical bridge spends ETH for gas on both the Ethereum and Linea sides. Bridging your entire ETH balance to Linea means that there will be no ETH for the gas on Ethereum when you want to withdraw.

Expecting fast withdrawals from the canonical bridge causes frustration. The proof generation cycle takes several hours. In case of time constraint, use a third-party bridge for withdrawals but keep in mind the different security assumptions of that solution.

Not completing the claim process on Ethereum is another mistake that causes many problems. The canonical Linea Bridge requires the manual claiming transaction on the Ethereum side after the zero-knowledge proof is verified. In case you do not go to the bridge interface to complete the claim, your funds will remain in the bridge contract in the claimable state. The pending claims can be viewed on the bridge interface.

Key Points to Remember

The Linea Bridge bridges the tokens from Ethereum to Linea and vice versa using the canonical bridge that is integrated directly with the Linea protocol and secured with zero-knowledge proofs. Deposits from Ethereum to Linea are quick (usually a few minutes), while withdrawals from Linea to Ethereum require zero-knowledge proof generation and verification and take several hours. The gas for the transactions is spent on both sides and is paid in ETH. The third-party bridges like Across or Stargate allow completing the withdrawals in minutes but have different security assumptions. The interface of the official bridge is at bridge.linea.build and always checking the URL before connecting the wallet prevents phishing.