🛡️ VeilLend

Private Lending. Starknet Speed.

VeilLend is a privacy-first decentralized lending protocol built on Starknet. It leverages Zero-Knowledge (ZK) cryptography to enable users to deposit, borrow, and transact with complete financial privacy.

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🏆 Hackathon Track: Privacy

This project is built specifically for the Privacy Track, implementing:

• Confidential Transactions: Shielded pools for depositing and withdrawing assets without revealing the link between sender and receiver.
• ZK Protocol Implementation: Custom implementation of a Commit-Reveal Scheme using Poseidon Hashing (Starknet's native hash).
• Shielded Wallet UI: A privacy-focused mobile interface that masks sensitive balances and integrates directly with Starknet wallets.

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🏗️ Architecture

The project follows a modern, layered architecture:

Component	Tech Stack	Description
Smart Contracts	Cairo 2.x	On-chain logic for Lending Pools, ZK Shielding, and Asset Management.
Mobile App	React Native (Expo)	Cross-platform mobile wallet interface with "Privacy Mode" and Starknet SDK integration.
Backend API	NestJS	Relayer service, indexer, and off-chain data aggregator backed by Supabase.
Database	PostgreSQL (Supabase)	Stores encrypted user profiles, transaction history, and active positions.

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🔐 Smart Contracts (Cairo)

Located in /contracts, our smart contracts power the privacy engine:

1. ZK Shielded Pool (zk_shield.cairo)

• Implements a Commit-Reveal privacy scheme.
• Deposit: Users generate a secret off-chain, hash it (Poseidon), and deposit funds with the commitment.
• Withdraw: Users provide the secret (nullifier) to prove ownership without revealing their identity.
• Privacy: The on-chain state only tracks hashed commitments, breaking the link between deposit and withdrawal.

2. Lending Pool (lending_pool.cairo)

• Standard DeFi logic for Supply, Borrow, and Repay.
• Integrated with ERC20 tokens (ETH, USDC).
• Emits events for real-time indexing.

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📱 Mobile App Features

• 🛡️ Shielded Dashboard: Toggle "Privacy Mode" to mask balances and positions from prying eyes (or shoulder surfers).
• 🔑 Starknet Login: Authenticate securely using cryptographic signatures (Argent/Braavos) via starknet-react.
• ⚡ Fast Actions: One-tap Deposit, Borrow, and Repay flows.
• 🔄 Real-time Updates: Live synchronization with on-chain data via the Backend API.

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🚀 Getting Started

Prerequisites

• Node.js (v18+)
• Scarb (for Cairo contracts)
• Expo Go (for mobile testing)

1. Smart Contracts

cd contracts
scarb build
# Deploy artifacts from target/dev/

2. Backend API

cd veilend-backend
npm install
# Setup .env with SUPABASE_URL and SUPABASE_KEY
npm run start:dev
# Swagger Docs available at http://localhost:3000/api

3. Mobile App

cd mobile-app
npm install --legacy-peer-deps
npx expo start
# Scan QR code with Expo Go

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🛠️ Tech Deep Dive: ZK Privacy Flow

1. Client-Side: User selects "Shielded Deposit". App generates a random secret.
2. Hashing: App computes commitment = Poseidon(secret).
3. On-Chain: App calls deposit_shielded(amount, commitment).
4. Storage: Contract stores commitment mapped to amount.
5. Withdrawal: User provides secret to a fresh address. Contract verifies Poseidon(secret) == commitment and transfers funds.

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📜 License

MIT