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. ```solidity // 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 ```solidity // 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. ```solidity // 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: ```json { "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 ```solidity 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: ```solidity 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) ```solidity interface IERC2981 { function royaltyInfo(uint256 tokenId, uint256 salePrice) external view returns (address receiver, uint256 royaltyAmount); } ``` ## NFT Minting Strategies ### Standard Minting ```solidity function mint(address to) public { uint256 tokenId = totalSupply() + 1; _mint(to, tokenId); } ``` ### Presale và Whitelist ```solidity 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: ```solidity 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 ```solidity // 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 ```solidity bool private locked; modifier nonReentrant() { require(!locked, "Reentrant call"); locked = true; _; locked = false; } ``` ### Access Control ```solidity mapping(address => bool) public authorizedMinters; modifier onlyAuthorized() { require(authorizedMinters[msg.sender] || msg.sender == owner, "Not authorized"); _; } ``` ### Input Validation ```solidity 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. 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