NFT và Digital Assets - Sở hữu Kỹ thuật số trên Blockchain

NFT và Digital Assets - Sở hữu Kỹ thuật số trên Blockchain

NFT (Non-Fungible Tokens) đã trở thành hiện tượng, thay đổi cách chúng ta sở hữu và giao dịch digital assets. Bài viết này khám phá thế giới NFT.

NFT là gì?

Non-Fungible Token

NFT là token unique, không thể thay thế, đại diện cho quyền sở hữu một asset cụ thể.

Fungible vs Non-Fungible

Fungible (ERC-20)	Non-Fungible (NFT)
Interchangeable	Unique
1 BTC = 1 BTC	Each NFT is different
Divisible	Indivisible (usually)
Example: Tokens	Example: Art, collectibles

Characteristics

• Unique: Mỗi NFT là duy nhất
• Indivisible: Không thể chia nhỏ (thường)
• Ownership: Provenance trên blockchain
• Verifiable: Dễ dàng verify authenticity

NFT Standards

ERC-721

Standard cho unique tokens trên Ethereum.

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

Basic ERC-721 Implementation

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import "@openzeppelin/contracts/token/ERC721/ERC721.sol";

contract MyNFT is ERC721 {
    uint256 private _tokenIds;
    mapping(uint256 => string) private _tokenURIs;
    
    constructor() ERC721("MyNFT", "MNFT") {}
    
    function mint(address to, string memory tokenURI) public returns (uint256) {
        _tokenIds++;
        uint256 newTokenId = _tokenIds;
        
        _mint(to, newTokenId);
        _setTokenURI(newTokenId, tokenURI);
        
        return newTokenId;
    }
    
    function tokenURI(uint256 tokenId) public view override returns (string memory) {
        return _tokenURIs[tokenId];
    }
}

ERC-1155

Multi-token standard, có thể represent cả fungible và non-fungible tokens.

// ERC-1155 allows both
contract MyMultiToken is ERC1155 {
    // Fungible: amount > 1
    // Non-fungible: amount = 1
    function mint(
        address to,
        uint256 id,
        uint256 amount,
        bytes memory data
    ) public {
        _mint(to, id, amount, data);
    }
}

So sánh Standards

Feature	ERC-721	ERC-1155
Use Case	Unique items	Both fungible & unique
Batch Transfer	No	Yes
Gas Efficiency	Higher	Lower (for batches)
Metadata	Per token	Per token ID

NFT Metadata

Token URI

NFTs thường store metadata off-chain:

{
  "name": "My Awesome NFT",
  "description": "This is a unique digital artwork",
  "image": "https://ipfs.io/ipfs/QmXxXxXx...",
  "attributes": [
    {
      "trait_type": "Color",
      "value": "Blue"
    },
    {
      "trait_type": "Rarity",
      "value": "Legendary"
    }
  ]
}

Storage Options

• IPFS: Decentralized storage (recommended)
• Arweave: Permanent storage
• Centralized: HTTP/HTTPS URLs (not recommended)

NFT Use Cases

Digital Art

• Artists: Sell artwork directly
• Collectors: Build collections
• Platforms: OpenSea, Foundation, SuperRare

Gaming

• In-game Items: Weapons, skins, characters
• Play-to-Earn: Earn NFTs by playing
• Virtual Real Estate: Land in metaverse

Music

• Albums: Exclusive releases
• Royalties: Artists earn from resales
• Concerts: Access tokens

Collectibles

• Sports: NBA Top Shot, Sorare
• Trading Cards: Digital collectibles
• Memes: Viral content as NFTs

Identity và Credentials

• Certificates: Educational certificates
• Memberships: Club memberships
• Licenses: Professional licenses

Real Estate

• Property Titles: Ownership records
• Fractional Ownership: Share properties
• Rental Agreements: Smart contracts

NFT Marketplaces

OpenSea

• Largest: Most popular marketplace
• Multi-chain: Ethereum, Polygon, Solana
• User-friendly: Easy to use interface

Other Marketplaces

• Foundation: Curated platform
• SuperRare: Exclusive art
• Rarible: Community-owned
• LooksRare: Token rewards for trading

Building NFT Marketplace

contract NFTMarketplace {
    struct Listing {
        address seller;
        uint256 price;
        bool active;
    }
    
    mapping(uint256 => Listing) public listings;
    IERC721 public nftContract;
    
    function listNFT(uint256 tokenId, uint256 price) external {
        require(nftContract.ownerOf(tokenId) == msg.sender, "Not owner");
        require(nftContract.isApprovedForAll(msg.sender, address(this)), "Not approved");
        
        listings[tokenId] = Listing({
            seller: msg.sender,
            price: price,
            active: true
        });
    }
    
    function buyNFT(uint256 tokenId) external payable {
        Listing memory listing = listings[tokenId];
        require(listing.active, "Not for sale");
        require(msg.value >= listing.price, "Insufficient payment");
        
        nftContract.safeTransferFrom(listing.seller, msg.sender, tokenId);
        payable(listing.seller).transfer(listing.price);
        
        delete listings[tokenId];
    }
}

Royalties và Secondary Sales

Royalty Mechanism

Artists có thể earn từ mỗi resale:

contract RoyaltyNFT is ERC721 {
    uint256 public royaltyPercentage = 5; // 5%
    address public artist;
    
    function _calculateRoyalty(uint256 salePrice) internal view returns (uint256) {
        return (salePrice * royaltyPercentage) / 100;
    }
}

EIP-2981 (Royalty Standard)

interface IERC2981 {
    function royaltyInfo(uint256 tokenId, uint256 salePrice)
        external
        view
        returns (address receiver, uint256 royaltyAmount);
}

NFT Minting Strategies

Standard Minting

function mint(address to) public {
    uint256 tokenId = totalSupply() + 1;
    _mint(to, tokenId);
}

Presale và Whitelist

mapping(address => bool) public whitelist;
bool public presaleActive;

function presaleMint() external {
    require(presaleActive, "Presale not active");
    require(whitelist[msg.sender], "Not whitelisted");
    // Mint logic
}

Dutch Auction

Giá giảm dần theo thời gian:

uint256 public startPrice = 1 ether;
uint256 public endPrice = 0.1 ether;
uint256 public duration = 1 hours;

function getCurrentPrice() public view returns (uint256) {
    uint256 elapsed = block.timestamp - startTime;
    if (elapsed >= duration) return endPrice;
    
    uint256 priceRange = startPrice - endPrice;
    return startPrice - (priceRange * elapsed / duration);
}

Gas Optimization cho NFTs

Batch Minting

// Inefficient ❌
function mintMultiple(address[] memory to) public {
    for (uint i = 0; i < to.length; i++) {
        _mint(to[i], i + 1);
    }
}

// More efficient ✅
function batchMint(address[] memory to) public {
    for (uint i = 0; i < to.length; i++) {
        _mint(to[i], totalSupply() + i + 1);
    }
}

Storage Optimization

• Use uint8 for small numbers
• Pack structs
• Use events for non-essential data

Security Considerations

Reentrancy Protection

bool private locked;

modifier nonReentrant() {
    require(!locked, "Reentrant call");
    locked = true;
    _;
    locked = false;
}

Access Control

mapping(address => bool) public authorizedMinters;

modifier onlyAuthorized() {
    require(authorizedMinters[msg.sender] || msg.sender == owner, "Not authorized");
    _;
}

Input Validation

function mint(address to, string memory uri) external {
    require(to != address(0), "Invalid address");
    require(bytes(uri).length > 0, "Empty URI");
    // Mint logic
}

NFT Analytics

Key Metrics

• Floor Price: Lowest listed price
• Volume: Total trading volume
• Holders: Number of unique owners
• Rarity: Statistical rarity scores

Tools

• NFTGo: NFT analytics platform
• Rarity.tools: Rarity rankings
• DappRadar: NFT market data

Future of NFTs

Trends

• Utility NFTs: More than just art
• Gaming: Play-to-earn integration
• Metaverse: Virtual items
• Fractionalization: Split ownership

Challenges

• Gas Costs: Expensive on Ethereum
• Scams: Rug pulls và fake projects
• Market Volatility: Price fluctuations

Kết luận

NFTs đang mở ra khả năng mới cho digital ownership và creativity. Hiểu về standards, marketplaces và security best practices giúp bạn tham gia ecosystem một cách an toàn và hiệu quả.

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