🛡️ ShadowBid — Private Sealed-Bid Auction Platform

A privacy-preserving sealed-bid auction platform built on Starknet, powered by zero-knowledge proofs.

Built for the Re{define} Hackathon — Privacy Track.

---

Overview

ShadowBid enables truly private auctions on-chain. Bids are committed as cryptographic hashes during the bidding phase and only revealed after the deadline. Zero-knowledge proofs ensure bid validity without exposing amounts.

How It Works

┌──────────┐    ┌──────────┐    ┌──────────┐    ┌──────────┐
│  CREATE   │───▶│   BID     │───▶│  REVEAL  │───▶│  SETTLE  │
│  AUCTION  │    │ (sealed)  │    │ (verify) │    │ (winner) │
└──────────┘    └──────────┘    └──────────┘    └──────────┘
     Seller         Bidders        Bidders        Anyone
  sets params    submit hash    reveal amount    settle & claim

1. Create — Seller creates an auction with item details, minimum price, and deadline
2. Bid — Bidders submit Poseidon hash commitments of their bids (amount stays hidden)
3. Reveal — After bidding closes, bidders reveal their bids; contract verifies against commitments
4. Settle — Highest valid bid wins; losers can claim refunds

Key Privacy Features

• 🔒 Sealed bids — Amounts hidden via Poseidon hash commitments
• 📜 ZK range proofs — Noir circuits prove bid ≥ min_price without revealing the amount
• 🛡️ Front-running protection — Nobody can see bids during the bidding phase
• ⚡ STARK verification — Garaga verifies Noir proofs on-chain

---

Tech Stack

Layer	Technology	Purpose
Smart Contracts	Cairo (Starknet)	Auction logic, bid storage, state machine
ZK Proofs	Noir + Garaga	Prove bid validity without revealing amounts
Frontend	Next.js + Starknet.js	User-facing auction interface
Wallet	StarknetKit	Wallet connection (Argent, Braavos)
Scaffold	Scaffold-Stark 2	Development framework

---

Project Structure

shadow-bid/
├── packages/
│   ├── snfoundry/          # Cairo smart contracts
│   │   ├── contracts/
│   │   │   └── src/
│   │   │       ├── lib.cairo
│   │   │       └── shadow_bid.cairo    # Main auction contract
│   │   └── scripts-ts/
│   │       └── deploy.ts               # Deployment script
│   ├── circuits/            # Noir ZK circuits
│   │   ├── Nargo.toml
│   │   └── src/
│   │       └── main.nr                 # Bid range proof circuit
│   └── nextjs/              # Frontend application
│       ├── app/
│       └── components/
├── package.json
└── README.md

---

Getting Started

Prerequisites

• Node.js (>= v22)
• Yarn
• Scarb (Cairo package manager)
• Starknet Foundry

Installation

# Clone the repository
git clone https://github.com/degenspot/shadow-bid.git
cd shadow-bid

# Install dependencies
yarn install

Development

# Terminal 1: Start local Starknet devnet
yarn chain

# Terminal 2: Deploy contracts
yarn deploy

# Terminal 3: Start the frontend
yarn start

Visit http://localhost:3000 to interact with the app.

Cairo Contract Development

# Compile contracts
yarn compile

# Run tests
yarn test

---

Hackathon Context

Detail	Value
Hackathon	Re{define} by Starknet Foundation
Track	Privacy ($9,675 STRK)
Timeline	Feb 1 – Feb 28, 2026
Submission	DoraHacks

---

Key Resources

• Starknet Docs
• Cairo Book
• Garaga Documentation
• Tongo SDK
• Scaffold-Stark 2

---

Team

Built with ❤️ for the Starknet Re{define} Hackathon.

License

MIT