Starknet’s Account Abstraction Workshop

In this workshop you will learn how to create an account contract with a single signer that uses the STARK-friendly elliptic curve to sign transactions. The final code is inspired by Open Zeppelin’s account contract.

After completing each step, run the associated script to verify it has been implemented correctly.

Use the Cairo book and the Starknet docs as a reference.

Setup

1. Clone this repository
2. Create a new file called account.cairo inside the src folder
3. Copy the following starting code into the file

#[starknet::interface]
trait IAccount<T> {
    fn __execute__(self: @T);
    fn __validate__(self: @T);
}

#[starknet::contract(account)]
mod Account {
    use super::IAccount;

    #[storage]
    struct Storage {}

    #[abi(embed_v0)]
    impl AccountImpl of IAccount<ContractState> {
        fn __execute__(self: @ContractState){}
        fn __validate__(self: @ContractState){}
    }
}

Note: You'll be working on the account.cairo file to complete the requirements of each step. The file prev_solution.cairo will show up in future steps as a way to catch up with the workshop if you fall behind. Don't modify that file.

The next setup steps will depend on wether you prefer using Docker to manage global dependencies or not.

Option 1: Without Docker

4. Install the latest version of Scarb (instructions)
5. Install the latest version of Starknet Foundry (instructions)
6. Install Nodejs 20 or higher (instructions)
7. Install the Cairo 1.0 extension for VSCode (marketplace)
8. Run the tests to verify the project is setup correctly

$ scarb test

Option 2: With Docker

4. Make sure Docker is installed and running
5. Install the Dev Containers extension for VSCode (marketplace)
6. Launch an instance of VSCode inside of the container by going to View -> Command Palette -> Dev Containers: Rebuild and Reopen in Container
7. Open VSCode's integrated terminal and run the tests to verify the project is setup correctly

$ scarb test

Note: All the commands shown from this point on will assume that you are using the integrated terminal of a VSCode instance running inside the container. If you want to run the tests on a different terminal you'll need to use the command docker compose run test.

Step 1

Checkout the step1 branch to enable the verification tests for this section.

$ git checkout -b step1 origin/step1

Goal

Collect the public_key associated with a signer that is passed to the constructor, and make it public through a function also called public_key.

Verification

When completed, execute the test suite to verify you've met all the requirements for this section.

$ scarb test

Hints

• A public_key is defined with a single felt

Step 2

Checkout the step2 branch to enable the verification tests for this section.

$ git checkout -b step2 origin/step2

If you fell behind, the file prev_solution.cairo contains the solution to the previous step.

Goal

Implement the function is_valid_signature as defined by the SNIP-6 standard.

Requirements

• If the signature was created by the signer associated with the account contract the function should return the short string 'VALID'.
• If the signature was created by a signer not associated with the account contract, the function should return any other felt that is not the short string 'VALID'.

Verification

When completed, execute the test suite to verify you've met all the requirements for this section.

$ scarb test

Hints

• Use the stored public_key to check the signature.
• A "short string" is just an ascii representation of a single felt.
• You can check signatures on the STARK-friendly curve with the syscall check_ecdsa_signature available in the ecdsa module.
• The short string 'VALID' can be hardcoded or read from the module starknet::VALIDATED.

Step 3

Checkout the step3 branch to enable the verification tests for this section.

$ git checkout -b step3 origin/step3

If you fell behind, the file prev_solution.cairo contains the solution to the previous step.

Goal

Implement the function __validate__ as defined by the SNIP-6 standard. This function is similar to is_valid_signature but instead of expecting the signature to be passed as an argument it verifies the transaction's signature.

Requirements

• If the transaction signature was created by the signer associated with the account contract the function should return the short string 'VALID'.
• If the transaction signature was created by a signer not associated with the account contract, the transaction should be halted and reverted with an error message.

Verification

When completed, execute the test suite to verify you've met all the requirements for this section.

$ scarb test

Hints

• You can read the transaction details which includes the transaction signature using the syscall get_tx_info from the starknet module.
• You can stop and revert a transaction with an error message using the assert function.
• The Call struct can be found in the module starknet::account.

Step 4

Checkout the step4 branch to enable the verification tests for this section.

$ git checkout -b step4 origin/step4

If you fell behind, the file prev_solution.cairo contains the solution to the previous step.

Goal

Protect the __validate__ function by making it callable only by the protocol which uses the zero address.

Requirements

• If the function is invoked by any other address, the transaction should be halted and reverted with an error message.

Verification

When completed, execute the test suite to verify you've met all the requirements for this section.

$ scarb test

Hints

• You can read who the caller is by using the syscall get_caller_address available in the starknet module.

Step 5

Checkout the step5 branch to enable the verification tests for this section.

$ git checkout -b step5 origin/step5

If you fell behind, the file prev_solution.cairo contains the solution to the previous step.

Goal

Implement the functions __validate_declare__ and __validate_deploy__ with the exact same logic as __validate__ and make them publicly accessible. The signature of both functions is shown below.

fn __validate_declare__(
    self: @ContractState,
    class_hash: felt252
) -> felt252

fn __validate_deploy__(
    self: @ContractState,
    class_hash: felt252,
    salt: felt252,
    public_key: felt252
) -> felt252

Requirements

• The return value of both functions is the same as __validate__ ('VALID' or halted transaction).
• Both functions should only be callable by the Starknet protocol (same as __validate__).

Verification

When completed, execute the test suite to verify you've met all the requirements for this section.

$ scarb test

Hints

• Create a private function to encapsulate the logic of __validate__ so it can be reused by __validate_declare__ and __validate_deploy__.
• By grouping private functions into its own trait they can be called as methods of self and the smart contract state doesn’t need to be explicitly passed.
• You can auto generate a trait from an implementation using the attribute generate_trait.

Step 6

Checkout the step6 branch to enable the verification tests for this section.

$ git checkout -b step6 origin/step6

If you fell behind, the file prev_solution.cairo contains the solution to the previous step.

Goal

Implement the function __execute__ as defined by the SNIP-6 standard.

Requirements

• The function should be able to handle a single contract call or multiple contract calls in sequence.
• The result of each call should be collected and returned as an array.
• If an empty array of calls is passed, the function should halt and revert the transaction.
• The function should only be called by the protocol (the zero address).

Verification

When completed, execute the test suite to verify you've met all the requirements for this section.

$ scarb test

Hints

• You can call other contracts using the low level syscall call_contract_syscall available in the starknet module.
• You can iterate over an array by using the loop keyword and the array method pop_front.

Step 7

Checkout the step7 branch to enable the verification tests for this section.

$ git checkout -b step7 origin/step7

If you fell behind, the file prev_solution.cairo contains the solution to the previous step.

Goal

Implement the function supports_interface from the SNIP-5 standard for the SNIP-6 interface.

Requirements

• When providing the interface_id of the SNIP-6 trait the function should return true.
• When providing any other value for interface_id the function should return false.

Verification

When completed, execute the test suite to verify you've met all the requirements for this section.

$ scarb test

Hints

• The interface_id of the SNIP-6 trait is 1270010605630597976495846281167968799381097569185364931397797212080166453709

Step 8

Checkout the step8 branch to enable the verification tests for this section.

$ git checkout -b step8 origin/step8

If you fell behind, the file prev_solution.cairo contains the solution to the previous step.

Goal

Limit execution of the functions __execute__, __validate__, __validate_declare__ and __validate_deploy__ to transactions of the latest version.

Requirements

• Attempting to execute an invoke, declare, and deploy_account transaction that is not of the latest version should result in the transaction being halted and reverted.
• Simulated transactions should be supported.

Verification

When completed, execute the test suite to verify you've met all the requirements for this section.

$ scarb test

Hints

• Simulated transactions use the same version as their real counterpart but offset by 2^128.

If the test suite passes, congratulations, you have created your first custom Starknet account contract thanks to account abstraction!

To deploy your account contract to testnet you have two options, to use starknet.js or starknet.py. Choose which step to go next based on your preference of using Typescript or Python.

• Step 9A (Typescript)
• Step 9B (Python)

Step 9A (Typescript)

Checkout the step9-js branch to get a deployment script based on starknet.js.

$ git checkout -b step9-js origin/step9-js

If you fell behind, the file prev_solution.cairo contains the solution to the previous step.

Goal

To deploy your account contract to Starknet's testnet using the deploy.ts script found in the scripts folder.

Dependencies

Run the command below from the project's root folder to install the deployment script dependencies.

$ npm install

Deployer Wallet

Create a wallet that the script can use to pay for the declaration of your account contract.

Steps

1. Create a wallet on Starknet testnet using the Argent X or Braavos browser extension.
2. Fund the wallet by using the Faucet or the Bridge.
3. Create a file in the project's root folder called .env
4. Export the private key of the funded wallet and paste it in the .env file using the key DEPLOYER_PRIVATE_KEY.

DEPLOYER_PRIVATE_KEY=<YOUR_FUNDED_TESTNET_WALLET_PK>

RPC Endpoint

Provide an RPC URL that the script can use to interact with Starknet testnet.

Steps

1. Create an account on Infura.
2. Create a new API Key for a Web3.
3. Copy the RPC URL for Starknet's testnet.
4. Paste the RPC URL in the .env file using the key RPC_ENDPOINT.

DEPLOYER_PRIVATE_KEY=<YOUR_FUNDED_TESTNET_WALLET_PK>
RPC_ENDPOINT=<YOUR_RPC_URL_FOR_STARKNET_TESTNET>

Run the Script

Run the script that will declare, deploy and use your account contract to send a small amount of ETH to another wallet as a test.

Steps

1. From project's root folder run npm run deploy
2. Follow the instructions from the terminal

If the script finishes successfully your account contract is ready to be used on Starknet testnet.

Step 9B (Python)

WIP