**3. Data trust in the virtual world**

After the 4th industrial revolution, the virtual world has grown rapidly. The real thing has been converted into data from the virtual world, and the virtual world has even played a role in leading the real world. Here, we have a question about the reliability of data about whether the real thing is becoming data accurately in the virtual world. In the virtual world, trust technology is emerging as an important issue. We can think of blockchain as one of these trust technologies.

Blockchain was first proposed in 2008 in Satoshi Nakamoto's paper "Bitcoin: P2P Electronic Money System". Blockchain can be said to be a technology that gives trust in transactions between individuals. A blockchain consists of blocks containing data and a chain that connects them. It is a blockchain to create and connect blocks, and consensus algorithms are used in this process. Any of the nodes participating in the network can create blocks, but not all generated blocks are connected, and only one block is recognized and connected. Since only one block among many blocks is connected to the previous block and the remaining blocks are discarded, consensus among participating nodes to select one block is essential. As a method of reaching consensus, consensus algorithms such as Proof of Work (PoW) and Proof of Stake (PoS) are used. If it is recognized as a unique block by all nodes, the node that created the block will receive cryptocurrency as a reward. This action is called mining, and a blockchain connected only with blocks created by mining is called a Canonical Chain.

Blockchain is developing and evolving as shown in **Table 1** [9]. Blockchain 1.0 was a period of innovation in the financial system with the advent of Bitcoin. Bitcoin is meaningful in that it attempts a single global financial system based on decentralization and decentralization, which are the core values of blockchain.


#### **Table 1.**

*Blockchain paradigm evolution direction.*

Blockchain 2.0 is a period of contract automation centered on Ethereum smart contracts. It made it possible to execute contracts with legal effect online only with computer code without a transaction intermediary. It is a period that showed the potential for development as an online trading platform. Blockchain 3.0 is the stage in which blockchain technology is spread and applied to various industries. In order to solve the problems of the previous blockchain, technological improvements such as changes in consensus algorithms, improvement of transaction processing speed, and in-house decision-making functions are being made [10]. While it is expected that artificial intelligence will be applied to more expanded fields in Blockchain 3.0, more various applications of blockchain and artificial intelligence are expected to appear in the Metaverse environment.

### **4. Blockchain-based Metaverse**

#### **4.1 Ethereum code**

Ethereum is a platform network designed to operate various decentralized applications (DApps), based on its own blockchain. Just as the basic framework and details of Internet standards were documented as RFCs, Ethereum Request for Comment (ERC) documents the details of Ethereum. In DApps using the Ethereum network, the basic protocol for issuing tokens is expressed as ERC-number as shown in **Table 2**. ERC-number is a protocol to follow when issuing tokens from DApps using the Ethereum network. Ethereum standard documents start with ERC-20, ERC-165, ERC-223, ERC-621, ERC-721, ERC-777, ERC-827, ERC-884, ERC-998, ERC-1155, ERC-1404 etc. [11].

Among them, ERC-20 is a protocol related to replaceable tokens, and ERC-20 tokens have the same value and function and can be exchanged with each other. The Ethereum project is issuing tokens based on ERC-20 and allowing investment and various businesses to take place.

ERC-721 is a protocol for NFT (Non-Fungible Tokens). NFT guarantees uniqueness by keeping encrypted transaction history permanently on the blockchain. Each token has a unique recognition value, authenticating the ownership of digital assets and assigning a value to the transaction. NFT has been mainly used to commemorate special moments or to collect digital assets, and recently it is creating a new digital content business by combining it with Metaverse.


**Table 2.** *ERC(Ethereum request for comment)-number.*
