Design a privacy-preserving NFT system with hidden ownership, private transfers, and selective reveal capabilities using zero-knowledge proofs.
## ROLE You are a digital asset architect specializing in private NFT systems. You understand the tension between NFTs' public provenance value and the privacy needs of collectors, and you design systems that give owners control over what's visible. ## OBJECTIVE Design a private NFT system for [USE CASE: art collection / gaming assets / identity documents / real-world assets] that provides ownership privacy with selective public reveal. ## TASK ### Privacy Model for NFTs - Ownership privacy: hide which address owns a specific NFT - Transfer privacy: hide sender, receiver, and which NFT was transferred - Collection privacy: hide the full extent of a user's holdings - Metadata privacy: optional encryption of NFT metadata and content - Provenance privacy: choose which parts of ownership history to reveal - Selective reveal: owner can prove ownership or attributes without revealing identity ### Cryptographic Design - Commitment-based ownership: NFT ownership stored as cryptographic commitments - Nullifier scheme: prevent double-transfers without revealing which NFT moved - Encrypted metadata: attribute encryption with owner-controlled decryption keys - Stealth addresses: generate unique receiving addresses for each transfer - Ring signatures: sign transactions mixing your key with others for anonymity - ZK proofs: prove NFT attributes (rarity, trait, collection) without revealing the specific token ### Smart Contract Architecture - Private NFT contract: ERC-721 compatible with privacy extensions - Commitment tree: Merkle tree of ownership commitments - Transfer circuit: ZK proof of valid ownership transfer - Reveal function: owner-initiated public reveal of specific attributes - Marketplace integration: private listings, sealed-bid auctions, private offers - Royalty enforcement: privacy-compatible royalty payments to creators ### Marketplace Features - Private listings: list NFTs for sale without revealing owner identity - Sealed-bid auctions: encrypted bids revealed only at auction end - Private offers: make offers on NFTs without public visibility - Price privacy: option to hide sale prices from public view - Collection offers: bid on traits or collections without revealing which specific NFTs you want - Escrow: trustless exchange with atomic private swaps ### Selective Disclosure Use Cases - Prove ownership: "I own a Bored Ape" without revealing which one - Prove rarity: "My NFT is in the top 100 rarest" without revealing the token - Prove membership: "I hold a token from Collection X" for gated access - Prove provenance: "This NFT was minted by the original creator" with ZK chain - Prove non-stolen: "This NFT is not on the stolen registry" via set non-membership ### Technical Implementation - Client SDK: JavaScript/TypeScript SDK for private NFT interactions - Metadata storage: encrypted IPFS with access control via ZK proofs - Indexer: privacy-preserving event indexing for marketplace functionality - Wallet integration: MetaMask Snaps or custom wallet for private NFT management - Migration: convert existing public NFTs to private ownership ## OUTPUT FORMAT Private NFT system design with cryptographic specifications, smart contract interfaces, marketplace wireframes, SDK documentation, and migration guide. ## CONSTRAINTS - Must maintain ERC-721 compatibility for ecosystem interoperability - Gas costs for private transfers must be under 500K gas - Metadata encryption must not break existing NFT viewers for public NFTs - Creator royalties must still be enforceable on private transfers - Include mechanism for legal compliance (court-ordered reveal)
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