Section 1: Bridge Overview

The zkEVM bridge is a smart contract that allows users to transfer assets between the LX and LY layers. L1-L2 in zkEVM is a decentralized bridge for secure access to assets. It is a combination of two smart contracts, one deployed on one chain and the second on another chain.

The L1 and L2 contracts in zkEVM are identical except for the deployment location. The Bridge L1 contract is located on the Ethereum mainnet and is used to manage asset transfers between Rollups, while the Bridge L2 contract is located on a specific Rollup and is responsible for asset transfers between the mainnet and a Rollup (or multiple Rollups).

Layer 2 interoperability allows assets to be migrated between different L2 networks using native mechanisms. The solution is embedded into the bridge smart contract.

Use the following figure to understand the Bridge protocol:

Bridge

Consider two networks; L1 and L2. Bridges interconnect assets between L1 and L2. To move from L1 to L2, users must lock assets in the source network (or Layer 1). The smart contract then mints an equivalent value representing the asset in the target network L2. Such minted assets are called “wrapped tokens”.

Once minting is complete, the user or recipient can claim the assets in the target network (L2).

The opposite operation can also be performed. That is, after destroying the Wrapped Token, the bridge unlocks the original assets in the original network.

As mentioned before, there is the possibility of a third channel, a bridge for cross-chain messaging. That is, sending data payloads from one network to another can be achieved using the Bridge and Claim operations of a bridge.