In this tutorial, we will create a privacy preserving application on Starknet.
We will use Noir to write the circuit, Cairo for the smart contract, and finally Garaga for gluing everything together.

Follow the steps, or run the command below to install all the dependencies at once:

make install

curl -L noirup.dev | bash
noirup --version 1.0.0-beta.1

Barretenberg is a proving backend for Noir.

curl -L bbup.dev | bash
bbup --version 0.67.0

Scarb is a Cairo package manager and compiler toolchain.

curl --proto '=https' --tlsv1.2 -sSf https://docs.swmansion.com/scarb/install.sh | sh -s -- -v 2.9.2

Starknet Foundry is a smart contract development framework for Starknet.

curl -L https://raw.githubusercontent.com/foundry-rs/starknet-foundry/master/scripts/install.sh | sh
snfoundryup

Garaga is a code generation tool, SDK, and Cairo library.
It is shipped with a Python CLI:

pip install garaga

nargo new circuit
cd circuit
nargo check

Fill the Prover.toml file with the inputs:

x = "1"
y = "2"

Execute the circuit to generate a witness:

nargo execute witness

Prove the circuit:

bb prove_ultra_keccak_honk -b ./target/circuit.json -w ./target/witness.gz -o ./target/proof

Generate a verifying key and verify the proof:

bb write_vk_ultra_keccak_honk -b ./target/circuit.json -o ./target/vk
bb verify_ultra_keccak_honk -k ./target/vk -p ./target/proof

In the project folder, run:

garaga gen --system ultra_keccak_honk --vk circuit/target/vk.bin --project-name contract
cd contract
scarb build

Create a foundry config file named snfoundry.toml inside the contract folder:

[sncast.default]
account = "test"
url = "https://starknet-sepolia.public.blastapi.io/rpc/v0_7"

Create a Starknet account:

sncast account create --type oz --name test

Go to https://starknet-faucet.vercel.app/ and paste the address of the account you created.
Use STRK as the fee token.

On Starknet all accounts are contracts, even your wallet, so you need to deploy an account contract to interact with your application.

sncast account deploy --fee-token strk --name test

Create a .secrets file in the contract folder and add the following variables:

SEPOLIA_RPC_URL="https://free-rpc.nethermind.io/sepolia-juno"
SEPOLIA_ACCOUNT_PRIVATE_KEY=<your_private_key>
SEPOLIA_ACCOUNT_ADDRESS=<your_address>

The values can be obtained by running:

sncast account list -p

First we need to declare the contract ("upload it's code hash to the network"):

garaga declare --fee strk

Then we can instantiate it (change class-hash according to the output on the previous step):

garaga deploy --fee strk --class-hash 0x62412c03a6d8f5d1b721757a67e5e2d092ae0bbbdb487eb1c7c598835324a76

garaga verify-onchain \
    --system ultra_keccak_honk \
    --contract-address 0x52691054da2ae92e7dd55afe4201adc6da412c97539f0f5b8687d069581165b \
    --proof ../circuit/target/proof \
    --vk ../circuit/target/vk \
    --fee strk