What is Ethereum cross-chain bridge? How to achieve asset transfer?

Blockchain technology has spawned many independent networks, such as Ethereum, Binance Smart Chain, Polygon, etc. Each network has its own unique design and protocol. However, this independence also presents the challenge of difficult assets and information flowing freely between different chains. For example, ERC-20 tokens on Ethereum cannot be used directly on the Polygon network. In order to solve this isolation problem, cross-chain bridges emerged and became the key infrastructure to connect different blockchain networks.

What is a cross-chain bridge?

1. A cross-chain bridge is a tool or protocol that allows assets, data or information to be transferred between different blockchain networks.

2. They are essentially connectors between different chains, allowing users to send digital assets from one chain to another without leaving the blockchain ecosystem.

3. The Ethereum cross-chain bridge specifically refers to the bridge connecting Ethereum with other chains (such as the Layer 2 network or the independent Layer 1 network).

Overview of the working principle of cross-chain bridge

1. Most asset cross-chain bridges use the "lock-casting" or "destruction-casting" mechanism to achieve asset transfer.

2. When the user wants to transfer assets from Chain A to Chain B, the original assets on Chain A will be locked in a smart contract.

3. At the same time, on Chain B, an equal amount of "mapping tokens" or "encapsulated tokens" (such as WETH or WBNB) of the asset will be minted (issued) based on the number of assets locked on Chain A.

4. When the user wants to transfer assets from chain B to chain A, the mapping tokens on chain B will be destroyed, and the corresponding number of original assets on chain A will be unlocked and returned to the user.

Process of transferring assets through cross-chain bridge

1. The user selects the assets and target chains to be transferred and initiates a transfer request on the application interface of the cross-chain bridge.

2. The user approves the transaction and sends the assets to the cross-chain bridge to lock in the smart contract on the source chain.

3. Events on the source chain (assets have been locked) will be monitored by network participants such as Relayers, Validators, or Oracles.

4. This information is then safely transmitted to the target chain.

5. After the smart contract on the target chain verifys the validity of the information received, it will mint or release the corresponding number of mapped assets for the user at the address of the target chain.

6. Users can use these cross-chain assets on the target chain.

Several common types of cross-chain bridges

1. Centralized bridges rely on one or a few trusted third parties to keep assets and verify transactions. This method is simple and fast, but there are single-point risk and trust problems.

2. Alliance-style bridges are jointly managed and verified by a group of pre-determined validators or multiple signature parties. It is more decentralized than centralized bridges, but it still requires trust in most validators.

3. Decentralized/trustless bridges are designed to eliminate or minimize trust in third parties through cryptographic proofs, incentive mechanisms, or license-free verification networks. This type of bridge is complex in design but provides greater security and no trust.

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