Simple Circuit: Your First Zero Knowledge Proof Project

This is your first project using Noir for generating zero knowledge proofs!

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📋 Project Overview

This project demonstrates a complete workflow for building, compiling, and verifying zero knowledge circuits using Noir. It serves as both a learning resource and a practical example for beginners.

Key Technologies

• Language: Noir (.nr file extension)
• Proving Backend: Barretenberg
• Proving Scheme: ultra_honk
• Project Type: Binary crate
• Creator: Aztec Network

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🎯 Your First Simple Circuit

Basic Circuit Example

fn main(x: Field, y: pub Field) {
    assert(x != y);
}

#[test]
fn test_circuit() {
    main(1, 2);
}

This circuit proves that you know a private value (x) that is not equal to a public value (y), without revealing x.

How It Works

1. Private Input x: Only known to the prover
2. Public Input y: Known to both prover and verifier
3. Assertion: assert(x != y) creates a constraint
4. Proof: Generates a zero knowledge proof that the constraint is satisfied

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📁 Repository Structure

simple_circuit/
├── README.MD                      # This file - Project overview
├── Basics.MD                      # Detailed guide to Noir basics & concepts
├── NOIR_GUIDE.md                  # Complete guide to Noir language
├── Nargo.toml                     # Project manifest
├── Prover.toml                    # Input values for testing
├── src/
│   └── main.nr                    # Main circuit entry point
├── 0. Installation/
│   └── README.MD                  # Installation & setup guide for macOS/Windows
└── target/
    ├── simple_circuit.json        # Compiled circuit bytecode
    ├── simple_circuit.gz          # Witness file
    ├── vk                         # Verification key
    ├── proof                      # Generated proof
    └── public_inputs              # Public inputs

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🚀 Quick Start

1. Install Dependencies

Follow the Installation Guide for:

• macOS or Windows setup
• Rust, Nargo, and Barretenberg installation
• Verification of all tools

2. Understand the Basics

Read Basics.MD to learn:

• Variable types in Noir
• Input visibility (private vs public)
• Testing functions
• Complete workflow (check → compile → execute → prove → verify)

3. Learn the Language

Check NOIR_GUIDE.md for:

• Language features and syntax
• Common patterns
• Best practices
• Resources and documentation

4. Install compatible Barretenberg version

bbup --noir-version 1.0.0-beta.14

5. Run Your First Proof

# 1. Compile circuit
nargo compile

# 2. Generate verification key (one-time)
bb write_vk -b ./target/simple_circuit.json -o ./target

# 3. Execute to generate witness
nargo execute

# 4. Generate proof
bb prove -b ./target/simple_circuit.json -w ./target/simple_circuit.gz -o ./target

# 5. Verify proof
bb verify -k ./target/vk -p ./target/proof

6. Run the Frontend Demo

node server.js
# Open http://localhost:3000

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📖 Documentation Files

File	Purpose
README.MD (this file)	Project overview and quick start
Basics.MD	Detailed Noir basics, types, and workflow
NOIR_GUIDE.md	Comprehensive Noir language guide
0. Installation/README.MD	Step-by-step installation for macOS & Windows

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🔍 Understanding the Workflow

1. Nargo Check ✓

• Validates circuit structure
• Creates Prover.toml for inputs

2. Nargo Compile 📦

• Compiles Noir to ACIR (Arithmetic Circuit IR)
• Creates circuit bytecode

3. Nargo Execute ⚙️

• Executes circuit with test inputs
• Generates witness file (simple_circuit.gz)
• Stores witness in /target

4. BB Write VK 🔑

• Generates verification key from circuit
• Creates vk file for proof verification

5. BB Prove 🎯

• Uses Barretenberg to create proof
• Combines circuit + witness
• Outputs proof and public_inputs

6. BB Verify ✅

• Verifies proof off-chain
• Uses verification key
• Confirms proof validity without executing circuit

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💡 Key Learnings

About Noir

• DSL for ZKPs: Designed specifically for zero knowledge proofs
• Rust-like Syntax: Familiar to modern programmers
• Type-Safe: Strong type system prevents errors
• Backend Agnostic: Can compile to different proving systems

About Circuits

• Private vs Public: Control input visibility
• Assertions: Create constraints that must be satisfied
• Witness: The satisfying assignment that proves the constraint
• Proof: Cryptographic evidence without revealing witness

About Barretenberg

• Ultra-Honk Scheme: Modern proving system
• High Performance: Optimized for production use
• Multi-threaded: Uses parallel processing for efficiency
• Aztec-Built: Developed by Aztec for their privacy network

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🔧 Project Files Explained

Nargo.toml - Project Manifest

[package]
name = "simple_circuit"
type = "bin"
authors = ["Your Name"]
compiler_version = "0.21.0"

• Type: bin means binary crate (executable)
• Dependencies: Add libraries here as needed

Prover.toml - Test Inputs

x = "1"
y = "2"

• Private Inputs: Values for x, z, etc.
• Public Inputs: Values for pub parameters
• Updated after each nargo execute

src/main.nr - Circuit Code

fn main(x: Field, y: pub Field) {
    assert(x != y);
}

• Entry Point: Main circuit logic
• Functions: Define circuit behavior
• Tests: Validate circuit logic

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📚 Additional Resources

Official Documentation

• Noir Book: https://noir-lang.org/docs/
• Aztec Network: https://aztec.network/
• GitHub Repository: https://github.com/noir-lang/noir

Community

• Discord: Aztec Network community
• GitHub Discussions: Ask questions
• Forum: https://forum.aztec.network/

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🎓 Next Steps

Beginner

• ✅ Understand basic circuit structure
• ✅ Learn input visibility (private vs public)
• ✅ Generate your first proof
• 🔲 Write custom constraints

Intermediate

• 🔲 Build more complex circuits
• 🔲 Use cryptographic functions (SHA256, ECDSA)
• 🔲 Create reusable code patterns
• 🔲 Optimize circuit size

Advanced

• 🔲 Build library crates
• 🔲 Integrate with smart contracts
• 🔲 Create proving backends
• 🔲 Contribute to Noir ecosystem

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💫 About This Repository

This is a learning project for exploring:

• Zero knowledge proof fundamentals
• Noir programming language
• Barretenberg proving system
• ZK circuit development workflow

Feel free to fork, modify, and learn!

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📝 Notes

• All examples use the BN254 elliptic curve (Barretenberg default)
• Proofs are verified using ultra_honk scheme
• Generated proofs are non-interactive and publicly verifiable
• This project uses test inputs for demonstration

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