Bonus 5: Privacy-Focused Smart Contracts

🎯 Goal

Explore the bleeding edge of privacy-preserving smart contract platforms and zero-knowledge virtual machines. We’ll build an understanding of tools like Aztec (zkRollups + ZKVM), Noir (Rust-inspired zk language), and DarkFi (anonymous smart contracts using mixnets and ZK).

🧠 1. Why Privacy in Smart Contracts?

Smart contracts on public blockchains (e.g., Ethereum):

• Are fully transparent by default
• Leak user balances, interactions, and logic
• Cannot natively enforce confidentiality

✨ Enter ZK Smart Contracts

These platforms aim to:

• Obfuscate who interacts with what
• Hide balances, logic, state
• Enable private voting, anonymous DAOs, confidential DeFi

🧩 2. Key Platforms Overview

🛠 3. Toolchain: Noir (by Aztec)

Noir is a high-level DSL for writing zero-knowledge circuits, powering Aztec’s ZKVM.

📦 Install nargo (Noir CLI)

curl -L https://github.com/noir-lang/noirup/releases/latest/download/noirup-x86_64-unknown-linux-gnu.tar.gz | tar xz
sudo mv noirup /usr/local/bin/
noirup

Or with cargo:

cargo install --locked --git https://github.com/noir-lang/noir noirup
noirup

🧪 4. Write a Private Circuit

📝 program/src/main.nr

fn main(private x: Field, public y: Field) {
    assert(x * x == y);
}

This proves you know the square root of a public value without revealing the root.

🔧 Build + prove

nargo new square_proof
cd square_proof
# Paste code into `src/main.nr`
nargo build
nargo prove
nargo verify

If successful:

Proof verified successfully

🧪 5. Advanced Noir Ideas

You can encode:

• Private auctions (sealed bids)
• Private voting (no voter exposure)
• Hidden transfer logic
• Mixers, ZK games

Explore:

git clone https://github.com/noir-lang/noir-examples
cd noir-examples

Try:

cd voting
nargo build && nargo prove && nargo verify

🌑 6. DarkFi (Darknet Smart Contracts)

DarkFi is a new anonymous smart contract platform designed for activism, counter-economics, and encrypted societies.

Key Features:

• Mixnet-layer routing
• Anonymous accounts
• Private DAOs & governance
• Ring sigs + ZKPs for authentication

📦 Try the CLI

git clone https://git.dark.fi/darkfi
cd darkfi
make
./target/release/darkfi-wallet

Create an Identity:

darkfi-wallet keygen
darkfi-wallet balance

Join IRC (via Cwtch or Element) to coordinate and test early contracts.

⚖️ 7. Aztec (Encrypted zkRollup on Ethereum)

Aztec combines zkRollups with a private Ethereum-like VM for fully encrypted smart contracts.

💡 Encrypted State

• All user data, contract logic, and execution is encrypted
• ZK proofs enforce correctness

As of mid-2025:

• Aztec 3 is launching public devnet
• Noir is the core contract language
• Onboarding soon for devs via https://aztec.network

🧠 8. Compare Platforms

📝 9. Journal & Git Commit

✍️ Reflect on Smart Contract Privacy

echo "Bonus 5: Explored privacy-preserving smart contracts using Noir, Aztec, and DarkFi. Built a ZK circuit in Noir, proved secret knowledge without leaking inputs. Learned about encrypted state VMs and darknet-oriented smart contract chains." >> notes/bonus5_privacy_contracts.md

📦 Git Commit

git add .
git commit -S -m "Bonus 5 – Privacy Smart Contracts with Noir, Aztec, and DarkFi"

✅ Bonus 5 Checklist

• Installed Noir and nargo
• Built and verified a private computation
• Explored Noir examples: voting, auctions
• Explored DarkFi for full anonymity
• Compared contract platforms
• Journaled and signed commit

🧭 Up Next Bonus Options

• Bonus 6: I2P & Garlic Routing
• Bonus 7: Post-Quantum Cryptography (Kyber, Dilithium)
• Bonus 8: Running a Private Relay Node (mixnet, Tor bridge, Nym)

📌 Notes

• Noir + Aztec aim to make ZK coding feel like Rust + Solidity
• DarkFi is built from scratch as a “darknet for smart contracts”
• These tools will power future anonymous orgs, ZK-DAOs, and financial privacy layers