✍️ 필사 모드: Blockchain & Web3 Fully Explained — How Bitcoin, Ethereum, DeFi, NFTs, and DAOs Work

Table of Contents

1. Blockchain Fundamentals
2. Bitcoin
3. Ethereum and Smart Contracts
4. Layer 2 Scaling
5. DeFi — Decentralized Finance
6. NFTs — Digital Ownership
7. DAOs — Decentralized Autonomous Organizations
8. Web3 Vision vs Reality
9. 2026 Blockchain Trends
10. Blockchain for Developers

1. Blockchain Fundamentals

1.1 What Is a Blockchain?

A blockchain is a distributed ledger technology that bundles transaction records into blocks and chains them together. Without any central authority, all network participants share the same ledger, and once data is recorded, it is practically immutable.

Key properties:

1.2 Block Structure

Each block consists of a Header and a Body.

+------------------------------+
|        Block Header          |
| - Previous block hash        |
| - Timestamp                  |
| - Nonce                      |
| - Merkle Root                |
+------------------------------+
|        Block Body            |
| - Transaction 1              |
| - Transaction 2              |
| - ...                        |
+------------------------------+

Because the current block header includes the hash of the previous block, modifying any past block would require recalculating every subsequent block. This is the fundamental principle behind blockchain's immutability.

1.3 Hash Functions and Merkle Trees

The most critical cryptographic tool in blockchain is the hash function. Taking SHA-256 as an example, it produces a fixed-length (256-bit) output from any input, and even the smallest change in input produces a completely different hash.

import hashlib

data = "Hello, Blockchain!"
hash_value = hashlib.sha256(data.encode()).hexdigest()
print(hash_value)
# Output: a fixed-length 64-character hexadecimal string

A Merkle Tree repeatedly hashes pairs of transaction hashes to produce a single root hash. This allows efficient verification of whether a specific transaction is included in a block without downloading all the data.

1.4 Consensus Algorithms

Consensus algorithms determine "what goes into the next block" in a distributed network.

Proof of Work (PoW)

Miners repeatedly compute hashes to find a nonce value that satisfies certain conditions. Because this requires enormous computational resources, an attacker would need to control more than 51% of the total computing power to manipulate the network.

Goal: Find a nonce where hash starts with 0000

nonce=0  -> hash: a3f2b1c9...  (does not meet condition)
nonce=1  -> hash: 8d1e7f4a...  (does not meet condition)
...
nonce=N  -> hash: 0000ab3f...  (condition met! Block created!)

The advantage is proven security; the disadvantage is massive power consumption.

Proof of Stake (PoS)

Validators stake (deposit) a certain amount of tokens and earn the right to create blocks proportional to their stake. Energy consumption drops by over 99% compared to PoW, and malicious behavior results in slashing of staked assets.

Other variants include DPoS (Delegated Proof of Stake), PBFT (Practical Byzantine Fault Tolerance), and PoA (Proof of Authority).

1.5 Public vs Private Blockchains

2. Bitcoin

2.1 Satoshi Nakamoto and the Birth of Bitcoin

In October 2008, a pseudonymous figure called Satoshi Nakamoto published a whitepaper titled "Bitcoin: A Peer-to-Peer Electronic Cash System." On January 3, 2009, the genesis block (Block 0) was mined, launching the Bitcoin network.

Bitcoin was designed to be a system that enables online payments without a trusted third party.

2.2 The UTXO Model

Bitcoin uses the UTXO (Unspent Transaction Output) model rather than an account balance model.

[Transaction Example]
Input:  5 BTC received from a previous TX (UTXO)
Output: 3 BTC to recipient (new UTXO created)
        1.999 BTC back to sender (change UTXO)
        0.001 BTC fee (goes to miner)

Every UTXO is either "spent" or "unspent." This model is advantageous for parallel processing and structurally prevents double spending.

2.3 The Halving

Bitcoin's block reward is halved approximately every four years (every 210,000 blocks).

The total supply is capped at 21 million BTC, with the last bitcoin expected to be mined around 2140. This deflationary design is one reason Bitcoin is called "digital gold."

2.4 The Lightning Network

Bitcoin's main chain can process only about 7 transactions per second. The Lightning Network was created to solve this scalability problem.

Two parties open a payment channel, conduct unlimited transactions within the channel, and then record only the final balance on the main chain. This enables micropayments to be processed almost instantly with extremely low fees.

Alice --- [Payment Channel] --- Bob
  |                              |
  |  Off-chain transactions      |
  |  (instant, low cost)         |
  |                              |
  +--- Final settlement ----> Main chain

3. Ethereum and Smart Contracts

3.1 Ethereum's Innovation

Proposed by Vitalik Buterin in 2013 and launched in 2015, Ethereum added programmable logic (smart contracts) to blockchain. If Bitcoin is "programmable money," Ethereum aims to be a "programmable world computer."

3.2 What Are Smart Contracts?

Smart contracts are code that automatically executes when predefined conditions are met. Once deployed on the blockchain, nobody can modify or stop them.

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

contract SimpleStorage {
    uint256 private storedValue;

    event ValueChanged(uint256 newValue);

    function set(uint256 value) public {
        storedValue = value;
        emit ValueChanged(value);
    }

    function get() public view returns (uint256) {
        return storedValue;
    }
}

This is a simple storage contract written in Solidity. The set function stores a value and get reads it. Once deployed, the code itself cannot be modified (except through upgrade patterns).

3.3 The EVM (Ethereum Virtual Machine)

The EVM is a Turing-complete virtual machine that runs identically on every node in the Ethereum network. It executes smart contract bytecode and guarantees deterministic execution so that all nodes reach the same result.

With many EVM-compatible chains (Polygon, BSC, Avalanche, Arbitrum, etc.), an ecosystem has formed where Solidity contracts can be deployed across multiple chains.

3.4 Gas and Fees

Every computation on Ethereum consumes Gas. Gas is a mechanism that prevents network abuse and rewards validators.

Transaction Cost = Gas Used x Gas Price (in Gwei)

Examples:
- Simple ETH transfer: 21,000 Gas
- ERC-20 token transfer: ~65,000 Gas
- Uniswap swap: ~150,000 Gas
- NFT minting: ~100,000-200,000 Gas

After EIP-1559 (London fork), the fee structure changed to Base Fee + Priority Fee, where the Base Fee is burned, reducing the ETH supply.

3.5 The Merge — Transition to PoS

In September 2022, Ethereum transitioned its consensus mechanism from PoW to PoS (The Merge). This resulted in:

• Approximately 99.95% reduction in energy consumption
• A minimum of 32 ETH required to become a validator
• Significantly reduced annual ETH issuance
• Block times stabilized at approximately 12 seconds

The Ethereum roadmap continues with the Surge, Verge, Purge, and Splurge, ultimately targeting over 100,000 transactions per second.

4. Layer 2 Scaling

4.1 Why Is Layer 2 Needed?

Ethereum's mainnet (Layer 1) can process only about 15-30 transactions per second. When usage surges, Gas prices skyrocket, making even simple transfers cost tens of dollars. Layer 2 solutions scale throughput by tens to hundreds of times while maintaining mainnet security.

4.2 Rollups

Rollups process multiple transactions off-chain and record compressed data on Layer 1.

Optimistic Rollups

Transactions are assumed valid by default (optimistic), with a challenge period (approximately 7 days) during which fraud proofs can be submitted.

• Representative projects: Optimism, Arbitrum, Base
• Advantage: High EVM compatibility allows deploying existing Solidity code with minimal changes
• Disadvantage: 7-day wait for withdrawals

ZK Rollups

Zero-Knowledge Proofs mathematically prove transaction validity. Validity proofs are submitted alongside data to Layer 1, enabling immediate finality.

• Representative projects: zkSync, StarkNet, Polygon zkEVM, Scroll, Linea
• Advantage: Immediate finality, higher security
• Disadvantage: Implementing EVM compatibility is technically challenging

4.3 Sidechains and Validium

Sidechains are independent chains with their own consensus mechanisms. Assets move between the mainnet and sidechain via bridges. Polygon PoS is a prime example.

Validium uses ZK proofs but stores data off-chain to further reduce costs. There is a trade-off between security and cost, as data availability (DA) is delegated externally.

4.4 Layer 2 Comparison

5. DeFi — Decentralized Finance

5.1 What Is DeFi?

DeFi (Decentralized Finance) is an ecosystem that provides financial services through smart contracts without traditional intermediaries like banks, brokerages, or insurance companies. Anyone with an internet connection and a wallet can participate.

5.2 DEX — Decentralized Exchanges

Unlike centralized exchanges (CEXs), DEXs primarily use the AMM (Automated Market Maker) model instead of order books.

Uniswap's core formula:

x * y = k

x = quantity of Token A
y = quantity of Token B
k = constant (liquidity pool size)

When a user deposits Token A and withdraws Token B, x increases and y decreases, automatically adjusting the price. This simple formula enables 24/7 trading without any central administrator.

Key DEXs:

• Uniswap: Pioneer of Ethereum-based AMMs; introduced concentrated liquidity in V3
• Curve Finance: Optimized for stablecoin swaps
• dYdX: Derivatives (futures/options) DEX
• Raydium / Jupiter: Solana-based DEXs

5.3 Lending Protocols

Lending protocols like Aave and Compound work as follows:

1. Lenders deposit assets into a pool
2. Borrowers provide collateral and take loans
3. Interest rates are determined algorithmically based on supply and demand
4. Automatic liquidation occurs when the collateral ratio falls below a threshold

[Liquidity Pool]
  Lender A: 100 ETH -> earns interest
  Lender B: 50 ETH  -> earns interest

  Borrower C: 200 USDC collateral -> borrows 1 ETH
  (Collateral ratio: ~150%)
  If collateral value drops -> automatic liquidation

5.4 Stablecoins

Stablecoins are tokens pegged to assets like the US dollar to reduce price volatility.

The 2022 Terra/LUNA collapse, where the algorithmic stablecoin UST depegged and wiped out approximately 40 billion dollars, powerfully illustrated the systemic risks of DeFi.

5.5 Liquidity Pools and Yield Farming

Liquidity providers (LPs) deposit token pairs into pools and receive a share of trading fees as rewards. When protocol token rewards are added on top, this becomes Yield Farming.

An important caveat is Impermanent Loss: if the deposited token pair experiences significant price divergence, the LP may suffer losses compared to simply holding.

6. NFTs — Digital Ownership

6.1 What Are NFTs?

NFTs (Non-Fungible Tokens) are unique, non-interchangeable tokens. While regular tokens (ERC-20) are interchangeable, each NFT (ERC-721) has a unique identifier.

// ERC-721 core interface (simplified)
interface IERC721 {
    function ownerOf(uint256 tokenId) external view returns (address);
    function transferFrom(address from, address to, uint256 tokenId) external;
    function approve(address to, uint256 tokenId) external;
}

6.2 NFT Use Cases

Digital Art and Collectibles: The most well-known use case. CryptoPunks and BAYC have sold for millions of dollars.

Gaming Items: In-game items and characters are issued as NFTs, granting true ownership and tradeability. Axie Infinity was an early representative example.

Music and Content: Artists sell directly to fans without intermediaries and automatically receive royalties on secondary sales.

Domain Names: Through ENS (Ethereum Name Service), users can own domains like yourname.eth as NFTs.

Real-World Asset Certificates: Experiments with issuing real estate ownership, event tickets, and memberships as NFTs are ongoing.

6.3 Utility NFTs

While the early NFT market was speculation-driven, the current trend is toward providing tangible utility.

• Community membership and access rights
• Tokens redeemable for physical goods
• Event admission tickets (POAPs, etc.)
• Voting and governance participation rights

6.4 The Current NFT Market

After the 2021-2022 hype, the NFT market went through a significant correction. Trading volumes have declined substantially from the peak, but the underlying technology infrastructure has matured. Standards continue to evolve from ERC-721 to ERC-1155 (multi-token) and ERC-6551 (token-bound accounts).

7. DAOs — Decentralized Autonomous Organizations

7.1 The DAO Concept

A DAO (Decentralized Autonomous Organization) is an organization governed by smart contracts. Instead of traditional boards of directors or CEOs, decisions are made through token holder votes.

[DAO Decision-Making Flow]
1. A member creates a Proposal
2. Token holders vote (set period, e.g., 7 days)
3. Quorum met + majority in favor -> execution
4. Smart contract auto-executes (fund transfers, parameter changes, etc.)

7.2 Governance Tokens

Governance tokens grant the right to participate in DAO decision-making.

Notable governance tokens:

• UNI: Uniswap protocol governance
• AAVE: Aave lending protocol governance
• MKR: MakerDAO (manages DAI issuance)
• ARB: Arbitrum chain governance
• ENS: Ethereum Name Service governance

7.3 Voting Mechanisms

Beyond simple majority voting, various methods are being explored.

Quadratic Voting: Tokens are used to vote, but casting n votes requires n-squared tokens. This prevents a few whales from monopolizing votes.

1 vote: 1 token required
2 votes: 4 tokens required
3 votes: 9 tokens required

Delegated Voting: A system where token holders delegate their voting power to experts. Designed for participants who cannot vote directly on every proposal.

7.4 Challenges Facing DAOs

• Low voter turnout: Most DAOs see actual participation rates below 10%
• Plutocracy: Large token holders dominate decisions
• Unclear legal status: Legal personhood of DAOs under existing frameworks
• Slow decision-making: On-chain voting takes days to weeks

8. Web3 Vision vs Reality

8.1 The Evolution of the Web

The core promise of Web3 is that users truly own their data and digital assets.

8.2 The Web3 Ideal

• Data sovereignty: Users own their data, not platforms
• Censorship resistance: Content cannot be deleted by central authorities
• Economic participation: Users share in network value
• Self-sovereign identity: Managing your own identity through DIDs
• Composability: Combining protocols like building blocks

8.3 Real-World Challenges

The UX barrier: Seed phrase management, Gas fees, and complex transaction signing present high entry barriers for average users.

Scalability: While Layer 2 has improved, the user experience still falls short of Web2 standards.

Security incidents: Smart contract hacks, bridge vulnerabilities, and phishing cause billions of dollars in losses annually.

Environmental concerns: The PoS transition has greatly improved things, but Bitcoin mining energy consumption remains contentious.

Regulatory uncertainty: Without established regulatory frameworks across jurisdictions, the business environment remains unstable.

8.4 The Decentralization Paradox

Despite Web3's goal of decentralization, centralized points exist in practice:

• Dependence on a few node service providers like Infura and Alchemy
• Dominant wallet software like MetaMask
• Hash rate concentration among a few large mining pools
• Token distribution skewed by VC investment
• The existence of admin keys in smart contracts

9. 2026 Blockchain Trends

9.1 RWA — Real World Asset Tokenization

The biggest topic in the 2025-2026 blockchain industry is RWA (Real World Assets) tokenization — issuing real estate, bonds, equities, and art as on-chain tokens.

• BlackRock BUIDL Fund: An on-chain fund tokenizing US Treasuries
• Ondo Finance: Tokenized US Treasury and bond products
• Centrifuge: Tokenizing corporate loans and invoices

Benefits of RWA:

• 24/7 trading
• Fractional ownership (own a portion of expensive real estate)
• Improved global accessibility
• Transparent audit trail

9.2 Institutional Adoption

Starting with the approval of Bitcoin spot ETFs in 2024, traditional financial institutions have rapidly accelerated their blockchain participation.

• Global banks building tokenization platforms
• Expansion of institutional-grade custody services
• Introduction of stablecoin payment infrastructure
• Development of regulatory frameworks (EU MiCA, US FIT21, etc.)

9.3 CBDCs — Central Bank Digital Currencies

Central banks worldwide are researching and issuing CBDCs (Central Bank Digital Currencies).

• Digital yuan (e-CNY): Already in pilot operation in China
• Digital euro: ECB in preparation phase
• Digital won: Bank of Korea conducting pilot programs

CBDCs use blockchain technology but are legal tender issued and managed by central banks. While philosophically opposed to decentralized cryptocurrencies, they may contribute to the mainstream adoption of blockchain infrastructure.

9.4 Convergence of AI and Blockchain

With the rapid growth of AI, blockchain integration use cases are increasing:

• AI agent payments: AI agents autonomously transacting with cryptocurrency
• Decentralized AI training: Data providers earning token rewards for contributing to AI training
• On-chain AI inference verification: Verifying AI model inference processes via blockchain
• AI DAOs: AI assisting or autonomously executing DAO governance processes

9.5 Account Abstraction

Account abstraction, represented by ERC-4337, is a game changer for Web3 UX:

• Wallet creation via social login instead of seed phrases
• Gas fee sponsorship by projects (Paymaster)
• Batched transactions
• Custom security rules like spending limits and time locks

10. Blockchain for Developers

10.1 Smart Contract Languages

Solidity is the de facto standard language for Ethereum and EVM-compatible chains.

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

import "@openzeppelin/contracts/token/ERC20/ERC20.sol";

contract MyToken is ERC20 {
    constructor(uint256 initialSupply) ERC20("MyToken", "MTK") {
        _mint(msg.sender, initialSupply * 10 ** decimals());
    }
}

Other languages:

• Vyper: Python-style Ethereum language focused on security
• Rust: Used on Solana (Anchor framework) and NEAR
• Move: Resource-oriented language used on Aptos and Sui
• Cairo: StarkNet-specific language

10.2 Development Tools

Hardhat — The most widely used Ethereum development environment

# Initialize project
npx hardhat init

# Compile contracts
npx hardhat compile

# Run tests
npx hardhat test

# Start local network
npx hardhat node

# Deploy
npx hardhat run scripts/deploy.js --network sepolia

Foundry — Rust-based high-speed development tools

# Initialize project
forge init my-project

# Build
forge build

# Test (tests written in Solidity)
forge test -vvv

# Deploy
forge script script/Deploy.s.sol --rpc-url sepolia --broadcast

10.3 Frontend Integration

Ethers.js is a JavaScript library for interacting with Ethereum.

import { ethers } from "ethers";

// Connect wallet
const provider = new ethers.BrowserProvider(window.ethereum);
const signer = await provider.getSigner();
const address = await signer.getAddress();

console.log("Connected:", address);

// Call contract
const contract = new ethers.Contract(contractAddress, abi, signer);
const result = await contract.get();
console.log("Stored value:", result.toString());

The Wagmi + Viem combination has recently gained popularity for React-based dApp development.

// Wallet connection with wagmi (React Hook)
import { useAccount, useConnect, useDisconnect } from "wagmi";

function WalletConnect() {
  const { address, isConnected } = useAccount();
  const { connect, connectors } = useConnect();
  const { disconnect } = useDisconnect();

  if (isConnected) {
    return (
      <div>
        <p>Connected: {address}</p>
        <button onClick={() => disconnect()}>Disconnect</button>
      </div>
    );
  }

  return (
    <button onClick={() => connect({ connector: connectors[0] })}>
      Connect Wallet
    </button>
  );
}

10.4 Security Best Practices

Smart contract security is critically important. Contracts are difficult to modify after deployment, and vulnerabilities directly translate to asset losses.

Key vulnerabilities:

Security tools:

• Slither: Static analysis tool
• Mythril: Symbolic execution-based security analysis
• OpenZeppelin: Audited security standard library
• Echidna: Fuzz testing tool

10.5 Blockchain Learning Roadmap

Stage 1: Fundamentals
  - Blockchain principles, cryptography basics
  - Solidity syntax, Remix IDE
  - ERC-20, ERC-721 standard understanding

Stage 2: Hands-on Development
  - Set up Hardhat or Foundry environment
  - Write tests and deploy
  - Frontend integration with Ethers.js / Viem

Stage 3: DeFi / NFT Projects
  - Implement AMMs and lending protocols
  - Build an NFT marketplace
  - Gas optimization

Stage 4: Advanced
  - Upgradeable contracts (Proxy patterns)
  - Cross-chain communication
  - ZK proof utilization
  - MEV (Miner Extractable Value) understanding

Conclusion

Blockchain technology is maturing beyond its early hype cycles. With RWA tokenization, institutional participation, and UX improvements through account abstraction converging, blockchain is no longer merely a vehicle for cryptocurrency speculation — it is becoming a pillar of financial infrastructure.

For developers, blockchain remains a challenging but rewarding field. Learning Solidity, understanding DeFi protocol architecture, and mastering smart contract security will be significant assets for future technology careers.

Whether Web3 will fully realize its ultimate promise of "an internet where individuals truly own their digital assets" remains to be seen. But the technological innovations emerging along the way — zero-knowledge proofs, distributed consensus, programmable money — are already transforming the real world.