🔐 zk-Age Verification in Noir

This project demonstrates a zero-knowledge circuit that verifies whether a user's private age meets a public minimum age threshold without revealing the actual age.

It integrates:

• A Noir circuit
• Proof generation via bb.js and bb CLI
• Solidity verifier tested with Foundry

Introduction

An example repo to verify Noir circuits (with bb backend) using a Solidity verifier.

• /circuits - contains the Noir circuits.
• /contract - Foundry project with a Solidity verifier and a Test contract that reads proof from a file and verifies it.
• /js - JS code to generate proof and save as a file.

Tested with Noir 1.0.0-beta.3 and bb 0.82.2

🔹 Prerequisites Section

• Noir 1.0.0-beta.3
• bb CLI version 0.82.2
• Foundry
• Node.js >= 18
• Yarn (npm install -g yarn)

🔹 Example Use Case or Circuit Summary

• Circuit Logic The circuit checks:

if age ≥ minimum_age {
flag = 1
} else {
flag = 0
}

Only the result (flag) is revealed publicly; the actual age remains private.

Installation / Setup

# Foundry
git submodule update

# Build circuits, generate verifier contract
(cd circuits && ./build.sh)

# Install JS dependencies
(cd js && yarn)

Proof generation in JS

# Use bb.js to generate proof and save to a file
(cd js && yarn generate-proof)

# Run foundry test to read generated proof and verify
(cd contract && forge test --optimize --optimizer-runs 5000 --gas-report -vvv)

Proof generation with bb cli

cd circuits

# Generate witness
nargo execute

# Generate proof
bb prove -b ./target/noir_solidity.json -w target/noir_solidity.gz -o ./target --oracle_hash keccak

# Split this proof and public inputs into two files

# Convert proof to hex, and slice first 4 bytes of metadata
PROOF_HEX=$(cat ./target/proof | od -An -v -t x1 | tr -d $' \n' | sed 's/^.\{8\}//')

NUM_PUBLIC_INPUTS=2
HEX_PUBLIC_INPUTS=${PROOF_HEX:0:$((32 * $NUM_PUBLIC_INPUTS * 2))}
SPLIT_HEX_PUBLIC_INPUTS=$(sed -e 's/.\{64\}/0x&,/g' <<<$HEX_PUBLIC_INPUTS)
PROOF_WITHOUT_PUBLIC_INPUTS="${PROOF_HEX:$((NUM_PUBLIC_INPUTS * 32 * 2))}"

# Save proof and public inputs to files
echo $PROOF_WITHOUT_PUBLIC_INPUTS | xxd -r -p > ./target/proof
echo "[\"$SPLIT_HEX_PUBLIC_INPUTS\"]" > ./target/public-inputs

# Run foundry test to read generated proof and verify
cd ..
(cd contract && forge test --optimize --optimizer-runs 5000 --gas-report -vvv)

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🧭 Ecosystem Attribution

This project is indexed in the Electric Capital Crypto Ecosystems Map.

Source: Electric Capital Crypto Ecosystems
Link: https://github.com/electric-capital/crypto-ecosystems
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Thank you for contributing and for reading the contribution guide! ❤️