Testnet Deployment

This chapter guides developers through the process of compiling, deploying, and interacting with a Starknet smart contract written in Cairo on the testnet. Earlier, the focus was on deploying contracts using a local node, Katana. This time, the deployment and interaction target the Starknet testnet.

Ensure the following commands run successfully on your system. If not, see the Basic Installation section:

    scarb --version  # For Cairo code compilation
    starkli --version  # To interact with Starknet

Smart Wallet Setup

A smart wallet comprises a Signer and an Account Descriptor. The Signer is a smart contract with a private key for signing transactions, while the Account Descriptor is a JSON file detailing the wallet’s address and public key.

In order for an account to be used as a signer it must be deployed to the appropriate network, Starknet Sepolia or mainnet, and funded. For this example we are going to use Sepolia Testnet. To deploy your wallet, visit Smart Wallet Setup. Now you’re ready to interact with Starknet smart contracts.

Creating a Signer

The Signer is an essential smart contract capable of signing transactions in Starknet. You’ll need the private key from your smart wallet to create one, from which the public key can be derived.

Starkli enables secure storage of your private key through a keystore file. This encrypted file can be accessed using a password and is generally stored in the default Starkli directory.

First, create the default directory:

    mkdir -p ~/.starkli-wallets/deployer

Then generate the keystore file. The signer command contains subcommands for creating a keystore file from a private key or completely create a new one. In this tutorial, we’ll use the private key option which is the most common use case. You need to provide the path to the keystore file you want to create. You can give any name to the keystore file, you will likely have several wallets. In this tutorial, we will use the name my_keystore_1.json.

    starkli signer keystore from-key ~/.starkli-wallets/deployer/my_keystore_1.json
    Enter private key:
    Enter password:

In the private key prompt, paste the private key of your smart wallet. In the password prompt, enter a password of your choice. You will need this password to sign transactions using Starkli.

How to get the private key?

Export the private key from your Braavos or Argent wallet. For Argent X, you can find it in the "Settings" section → Select your Account → "Export Private Key". For Braavos, you can find it in the "Settings" section → "Privacy and Security" → "Export Private Key".

While knowing the private key of a smart wallet is necessary to sign transactions, it’s not sufficient. We also need to inform Starkli about the signing mechanism employed by our smart wallet created by Braavos or Argent X. Does it use an elliptic curve? If yes, which one? This is the reason why we need an account descriptor file.

[OPTIONAL] The Architecture of the Starknet Signer

This section is optional and is intended for those who want to learn more about the Starknet Signer. If you are not interested in the details, you can skip it.

The Starknet Signer plays an instrumental role in securing your transactions. Let’s demystify what goes on under the hood.

Key Components:

  1. Private Key: A 256-bit/32-byte/64-character (ignoring the 0x prefix) hexadecimal key that is the cornerstone of your wallet’s security.

  2. Public Key: Derived from the private key, it’s also a 256-bit/32-byte/64-character hexadecimal key.

  3. Smart Wallet Address: Unlike Ethereum, the address here is influenced by the public key, class hash, and a salt. Learn more in Starknet Documentation.

To view the details of the previously created keystore file:

    cat ~/.starkli-wallets/deployer/my_keystore_1.json

Anatomy of the keystore.json File:

{
  "crypto": {
    "cipher": "aes-128-ctr",
    "cipherparams": {
      "iv": "dba5f9a67456b121f3f486aa18e24db7"
    },
    "ciphertext": "b3cda3df39563e3dd61064149d6ed8c9ab5f07fbcd6347625e081fb695ddf36c",
    "kdf": "scrypt",
    "kdfparams": {
      "dklen": 32,
      "n": 8192,
      "p": 1,
      "r": 8,
      "salt": "6dd5b06b1077ba25a7bf511510ea0c608424c6657dd3ab51b93029244537dffb"
    },
    "mac": "55e1616d9ddd052864a1ae4207824baac58a6c88798bf28585167a5986585ce6"
  },
  "id": "afbb9007-8f61-4e62-bf14-e491c30fd09a",
  "version": 3
}

  • version: The version of the smart wallet implementation.

  • id: A randomly generated identification string.

  • crypto: Houses all encryption details.

Inside crypto:

  • cipher: Specifies the encryption algorithm used, which in this case is AES-128-CTR.

    • AES (Advanced Encryption Standard): A globally accepted encryption standard.

    • 128: Refers to the key size in bits, making it a 128-bit key.

    • CTR (Counter Mode): A specific mode of operation for the AES cipher.

  • cipherparams: Contains an Initialization Vector (IV), which ensures that encrypting the same plaintext with the same key will produce different ciphertexts.

    • iv (Initialization Vector): A 16-byte hex string that serves as a random and unique starting point for each encryption operation.

  • ciphertext: This is the private key after encryption, securely stored so that only the correct password can reveal it.

  • kdf and kdfparams: KDF stands for Key Derivation Function. This adds a layer of security by requiring computational work, making brute-force attacks harder.

    • dklen: The length (in bytes) of the derived key. Typically 32 bytes.

    • n: A cost factor representing CPU/memory usage. A higher value means more computational work is needed, thus increasing security.

    • p: Parallelization factor, affecting the computational complexity.

    • r: Block size for the hash function, again affecting computational requirements.

    • salt: A random value that is combined with the password to deter dictionary attacks.

  • mac (Message Authentication Code): This is a cryptographic code that ensures the integrity of the message (the encrypted private key in this case). It is generated using a hash of both the ciphertext and a portion of the derived key.

Before to continue, we have to choose a rpc provider

Choosing an RPC Provider

There are three main options for RPC providers, sorted by ease of use:

  1. Infura or Alchemy: A step up in complexity. You’ll need to set up an API key and choose an endpoint. For Infura, it would look like https://starknet-sepolia.infura.io/v3/<API_KEY>. Learn more in the Infura documentation.

  2. Your Own Node: For those who want full control. It’s the most complex but offers the most freedom. Check out Chapter 3 of the Starknet Book or Kasar for setup guides.

  3. Free RPC vendor: These 2 networks are eligible for free RPC vendors: mainnet and sepolia. You can choose Blast or Nethermind

Creating an Account Descriptor

An Account Descriptor informs Starkli about your smart wallet’s unique features, such as its signing mechanism. You can generate this descriptor using Starkli’s fetch subcommand under the account command. The fetch subcommand takes your on-chain wallet address as input and generates the account descriptor file. The account descriptor file is a JSON file that contains the details of your smart wallet. We also have to pass the rpc provider here.

    starkli account fetch <SMART_WALLET_ADDRESS> --output ~/.starkli-wallets/deployer/my_account_1.json --rpc https://starknet-sepolia.public.blastapi.io/rpc/v0_7

Note: Here we used the Public RPC Endpoint v0.7 Starknet (Sepolia) Testnet from Blast. If you don't specify the rpc provider, Starkli will use Blast Sepolia endpoint anyway.

⚠️ Contract not found?

In case you face an error like this:

    Error: ContractNotFound

🟩 Solution:

It means you probably just created a new wallet and it has not been deployed yet. To accomplish this you have to fund your wallet with tokens and transfer tokens to a different wallet address. For Sepolia tokens you can check this faucet. For more ways to get Sepolia tokens, a detailed instructions can be found in the Get Sepolia Tokens section.

Still doesn't work?

Check if your wallet's testnet network isn't yet set with Sepolia, try again with your blast rpc url.

starknet account fetch ... --rpc https://starknet-sepolia.public.blastapi.io

After this process, search your wallet address on the Starknet explorer. To see the details, go back to Smart Wallet Setup.

After running the command, you’ll see a message like the one below. We’re using a Braavos wallet as an example, but the steps are the same for an Argent wallet.

    Account contract type identified as: Braavos
    Description: Braavos official proxy account
    Downloaded new account config file: ~/.starkli-wallets/deployer/my_account_1.json

After the acount descriptor file is generated, you can see its details, run:

    cat ~/.starkli-wallets/deployer/my_account_1.json

Here’s what a typical descriptor might look like:

{
  "version": 1,
  "variant": {
    "type": "braavos",
    "version": 1,
    "implementation": "0x5dec330eebf36c8672b60db4a718d44762d3ae6d1333e553197acb47ee5a062",
    "multisig": {
      "status": "off"
    },
    "signers": [
      {
        "type": "stark",
        "public_key": "0x49759ed6197d0d385a96f9d8e7af350848b07777e901f5570b3dc2d9744a25e"
      }
    ]
  },
  "deployment": {
    "status": "deployed",
    "class_hash": "0x3131fa018d520a037686ce3efddeab8f28895662f019ca3ca18a626650f7d1e",
    "address": "0x6dcb489c1a93069f469746ef35312d6a3b9e56ccad7f21f0b69eb799d6d2821"
  }
}

Note: The structure will differ if you use an Argent wallet.

Setting up Environment Variables

To simplify Starkli commands, you can set environment variables. Two key variables are crucial: one for the Signer’s keystore file location and another for the Account Descriptor file.

    export STARKNET_ACCOUNT=~/.starkli-wallets/deployer/my_account_1.json
    export STARKNET_KEYSTORE=~/.starkli-wallets/deployer/my_keystore_1.json
    export STARKNET_RPC=https://starknet-sepolia.public.blastapi.io/rpc/v0_7

Setting these variables makes running Starkli commands easier and more efficient.

Declaring Smart Contracts in Starknet

Deploying a smart contract on Starknet involves two steps:

  • Declare your contract’s code.
  • Deploy an instance of the declared code.

To get started, navigate to the src/ directory in the examples/Ownable-Starknet directory of the Starknet Book repo. The src/lib.cairo file contains a basic contract to practice with.

First, compile the contract using the Scarb compiler. If you haven’t installed Scarb, follow the installation guide in the basic installation section.

    scarb build

This creates a compiled contract in target/dev/ as ownable_starknet_ownable.compiled_contract_class.json (in Chapter 2 of the book we will learn more details about Scarb).

Declaring Your Contract

Run this command to declare your contract using the default Starknet Sequencer’s Gateway:

    starkli declare ./target/dev/ownable_starknet_ownable.contract_class.json

According to the STARKNET_RPC url, starkli can recognize the target blockchain network, in this case "sepolia", so it is not necessary explicitly specify it.

Unless you’re working with custom networks where it’s infeasible for Starkli to detect the right compiler version, you shouldn’t need to manually choose a version with --network and --compiler-version.

If you encounter an "Error: Invalid contract class," it likely means your Scarb’s compiler version is incompatible with Starkli. Follow the steps above to align the versions. Starkli usually supports compiler versions accepted by mainnet, even if Scarb’s latest version is not yet compatible.

After running the command, you’ll receive a contract class hash. This unique hash serves as the identifier for your contract class within Starknet. For example:

    Class hash declared: 0x04c70a75f0246e572aa2e1e1ec4fffbe95fa196c60db8d5677a5c3a3b5b6a1a8

You can think of this hash as the contract class’s address. Use a block explorer like StarkScan to verify this hash on the blockchain.

If the contract class you’re attempting to declare already exists, it is ok we can continue. You’ll receive a message like:

    Not declaring class as its already declared. Class hash:
    0x04c70a75f0246e572aa2e1e1ec4fffbe95fa196c60db8d5677a5c3a3b5b6a1a8

Deploying Smart Contracts on Starknet

To deploy a smart contract, you’ll need to instantiate it on Starknet’s testnet. This process involves executing a command that requires two main components:

  1. The class hash of your smart contract.

  2. Any constructor arguments that the contract expects.

In our example, the constructor expects an owner address. You can learn more about constructors in Chapter 13 of The Cairo Book.

The command would look like this:

    starkli deploy \
        <CLASS_HASH> \
        <CONSTRUCTOR_INPUTS>

Here’s a specific example with an actual class hash and constructor inputs (as the owner address use the address of your smart wallet so you can invoke the transfer_ownership function later):

    starkli deploy \
        0x04c70a75f0246e572aa2e1e1ec4fffbe95fa196c60db8d5677a5c3a3b5b6a1a8 \
        0x02cdAb749380950e7a7c0deFf5ea8eDD716fEb3a2952aDd4E5659655077B8510

After executing the command and entering your password, you should see output like the following:

    Deploying class 0x04c70a75f0246e572aa2e1e1ec4fffbe95fa196c60db8d5677a5c3a3b5b6a1a8 with salt 0x065034b27a199cbb2a5b97b78a8a6a6c6edd027c7e398b18e5c0e5c0c65246b7...
    The contract will be deployed at address 0x02a83c32d4b417d3c22f665acbc10e9a1062033b9ab5b2c3358952541bc6c012
    Contract deployment transaction: 0x0743de1e233d38c4f3e9fb13f1794276f7d4bf44af9eac66e22944ad1fa85f14
    Contract deployed:
    0x02a83c32d4b417d3c22f665acbc10e9a1062033b9ab5b2c3358952541bc6c012

The contract is now live on the Starknet testnet. You can verify its status using a block explorer like StarkScan. On the "Read/Write Contract" tab, you’ll see the contract’s external functions.

Interacting with the Starknet Contract

Starkli enables interaction with smart contracts via two primary methods: call for read-only functions and invoke for write functions that modify the state.

Calling a Read Function

The call command enables you to query a smart contract function without sending a transaction. For instance, to find out who the current owner of the contract is, you can use the get_owner function, which requires no arguments.

    starkli call \
        <CONTRACT_ADDRESS> \
        owner

Replace <CONTRACT_ADDRESS> with the address of your recently deployed contract. The command will return the owner’s address, which was initially set during the contract’s deployment:

    [
        "0x02cdab749380950e7a7c0deff5ea8edd716feb3a2952add4e5659655077b8510"
    ]

Invoking a Write Function

You can modify the contract’s state using the invoke command. For example, let’s transfer the contract’s ownership with the transfer_ownership function.

    starkli invoke \
        <CONTRACT_ADDRESS> \
        transfer_ownership \
        <NEW_OWNER_ADDRESS>

Replace <CONTRACT_ADDRESS> with the address of the contract and <NEW_OWNER_ADDRESS> with the address you want to transfer ownership to. If the smart wallet you’re using isn’t the contract’s owner, an error will appear. Note that the initial owner was set when deploying the contract:

    Execution was reverted; failure reason: [0x43616c6c6572206973206e6f7420746865206f776e6572].

The failure reason is encoded as a felt. o decode it, use the starkli’s parse-cairo-string command.

    starkli parse-cairo-string <ENCODED_ERROR>

For example, if you see 0x43616c6c6572206973206e6f7420746865206f776e6572, decoding it will yield "Caller is not the owner."

After a successful transaction on L2, use a block explorer like StarkScan or Voyager to confirm the transaction status using the hash provided by the invoke command.

To verify that the ownership has successfully transferred, you can call the get_owner function again:

    starkli call \
        <CONTRACT_ADDRESS> \
        owner

If the function returns the new owner’s address, the transfer was successful.

Congratulations! You’ve successfully deployed and interacted with a Starknet contract.