Token Extensions: Immutable Owner

With the Token Program, the SetAuthority instruction can be used to change a Token Account's owner to another account. The ImmutableOwner extension ensures that ownership of a Token Account cannot be reassigned.

In this guide, we WILL walk through an example of using Solana Playground. Here is the final script.

Understanding the Implications

So, why is this important? The addresses for Associated Token Accounts are derived based on the owner and the mint. This makes it easy to find the related Token Account for a specific owner.

If the owner of an existing Associated Token Account is changed, users may unintentionally transfer funds to an account under the assumption that it belongs to the original owner.

With Token Extensions, Associated Token Accounts have the ImmutableOwner extension enabled by default, preventing the ownership from being changed.

The ImmutableOwner extension can also be enabled for any new Token Account created by the Token Extension program.

Getting Started

Start by opening this Solana Playground link with the following starter code.

// Client
console.log("My address:", pg.wallet.publicKey.toString());
const balance = await pg.connection.getBalance(pg.wallet.publicKey);
console.log(`My balance: ${balance / web3.LAMPORTS_PER_SOL} SOL`);

If it is your first time using Solana Playground, you'll first need to create a Playground Wallet and fund the wallet with devnet SOL.

Info

If you do not have a Playground wallet, you may see a type error within the editor on all declarations of pg.wallet.publicKey. This type error will clear after you create a Playground wallet.

To get devnet SOL, run the solana airdrop command in the Playground's terminal, or visit this devnet faucet.

solana airdrop 5

Once you've created and funded the Playground wallet, click the "Run" button to run the starter code.

Add Dependencies

Let's start by setting up our script. We'll be using the @solana/web3.js and @solana/spl-token libraries.

Replace the starter code with the following:

import {
  clusterApiUrl,
  sendAndConfirmTransaction,
  Connection,
  Keypair,
  SystemProgram,
  Transaction,
} from "@solana/web3.js";
import {
  createAssociatedTokenAccount,
  createMint,
  createInitializeImmutableOwnerInstruction,
  createInitializeAccountInstruction,
  getAccountLen,
  ExtensionType,
  TOKEN_2022_PROGRAM_ID,
  setAuthority,
  AuthorityType,
} from "@solana/spl-token";
 
// Playground wallet
const payer = pg.wallet.keypair;
 
// Connection to devnet cluster
const connection = new Connection(clusterApiUrl("devnet"), "confirmed");
 
// Transaction signature returned from sent transaction
let transactionSignature: string;

Mint Setup

We'll first need to create a new Mint Account before we can create Token Accounts.

// Authority that can mint new tokens
const mintAuthority = pg.wallet.publicKey;
// Decimals for Mint Account
const decimals = 2;
 
// Create Mint Account
const mint = await createMint(
  connection,
  payer, // Payer of the transaction and initialization fees
  mintAuthority, // Mint Authority
  null, // Optional Freeze Authority
  decimals, // Decimals of Mint
  undefined, // Optional keypair
  undefined, // Options for confirming the transaction
  TOKEN_2022_PROGRAM_ID, // Token Extension Program ID
);

Associated Token Account

The ImmutableOwner extension is enabled by default for Associated Token Accounts created for Mint Accounts that are owned by the Token Extension Program.

Let's demonstrate this concept by creating an Associated Token Account for the Playground wallet.

// Create Associated Token Account for Playground wallet
const associatedTokenAccount = await createAssociatedTokenAccount(
  connection,
  payer, // Payer to create Token Account
  mint, // Mint Account address
  payer.publicKey, // Token Account owner
  undefined, // Confirmation options
  TOKEN_2022_PROGRAM_ID, // Token Extension Program ID
);

Attempting to change the owner of the Associated Token Account will result in an error.

try {
  // Attempt to change owner of Associated Token Account
  await setAuthority(
    connection, // Connection to use
    payer, // Payer of the transaction fee
    associatedTokenAccount, // Associated Token Account
    payer.publicKey, // Owner of the Associated Token Account
    AuthorityType.AccountOwner, // Type of Authority
    new Keypair().publicKey, // New Account Owner
    undefined, // Additional signers
    undefined, // Confirmation options
    TOKEN_2022_PROGRAM_ID, // Token Extension Program ID
  );
} catch (error) {
  console.log("\nExpect Error:", error);
}

Run the script by clicking the Run button. You can then inspect the error in the Playground terminal. You should see a message similar to the following:

Expect Error: { [Error: failed to send transaction: Transaction simulation failed: Error processing Instruction 0: custom program error: 0x22]
  logs:
   [ 'Program TokenzQdBNbLqP5VEhdkAS6EPFLC1PHnBqCXEpPxuEb invoke [1]',
     'Program log: Instruction: SetAuthority',
     'Program log: The owner authority cannot be changed',
     'Program TokenzQdBNbLqP5VEhdkAS6EPFLC1PHnBqCXEpPxuEb consumed 3057 of 200000 compute units',
     'Program TokenzQdBNbLqP5VEhdkAS6EPFLC1PHnBqCXEpPxuEb failed: custom program error: 0x22' ] }

Immutable Owner Token Account

Next, let's build a transaction to enable the ImmutableOwner extension for a new Token Account. Note that this can only be done for new Token Accounts.

First, let's generate a new keypair to use as the address of the Token Account.

// Random keypair to use as owner of Token Account
const tokenAccountKeypair = Keypair.generate();
// Address for Token Account
const tokenAccount = tokenAccountKeypair.publicKey;

Next, let's determine the size of the new Token Account and calculate the minimum lamports needed for rent exemption.

// Size of Token Account with extension
const accountLen = getAccountLen([ExtensionType.ImmutableOwner]);
// Minimum lamports required for Token Account
const lamports = await connection.getMinimumBalanceForRentExemption(accountLen);

With Token Extensions, the size of the Token Account will vary based on the extensions enabled.

Build Instructions

Next, let's build the set of instructions to:

Create a new account
Initialize the ImmutableOwner extension
Initialize the remaining Token Account data

First, build the instruction to invoke the System Program to create an account and assign ownership to the Token Extensions Program.

// Instruction to invoke System Program to create new account
const createAccountInstruction = SystemProgram.createAccount({
  fromPubkey: payer.publicKey, // Account that will transfer lamports to created account
  newAccountPubkey: tokenAccount, // Address of the account to create
  space: accountLen, // Amount of bytes to allocate to the created account
  lamports, // Amount of lamports transferred to created account
  programId: TOKEN_2022_PROGRAM_ID, // Program assigned as owner of created account
});

Next, build the instruction to initialize the ImmutableOwner extension for the Token Account.

// Instruction to initialize the ImmutableOwner Extension
const initializeImmutableOwnerInstruction =
  createInitializeImmutableOwnerInstruction(
    tokenAccount, // Token Account address
    TOKEN_2022_PROGRAM_ID, // Token Extension Program ID
  );

Lastly, build the instruction to initialize the rest of the Token Account data.

// Instruction to initialize Token Account data
const initializeAccountInstruction = createInitializeAccountInstruction(
  tokenAccount, // Token Account Address
  mint, // Mint Account
  payer.publicKey, // Token Account Owner
  TOKEN_2022_PROGRAM_ID, // Token Extension Program ID
);

Send Transaction

Next, let's add the instructions to a new transaction and send it to the network. This will create a Token Account with the ImmutableOwner extension enabled.

// Add instructions to new transaction
const transaction = new Transaction().add(
  createAccountInstruction,
  initializeImmutableOwnerInstruction,
  initializeAccountInstruction,
);
 
// Send transaction
transactionSignature = await sendAndConfirmTransaction(
  connection,
  transaction,
  [payer, tokenAccountKeypair], // Signers
);
 
console.log(
  "\nCreate Token Account:",
  `https://solana.fm/tx/${transactionSignature}?cluster=devnet-solana`,
);

Run the script by clicking the Run button. You can then inspect the transaction details on SolanaFM.

If you attempt to change the owner of the Token Account, then you should see the same error as before.

try {
  // Attempt to change owner of Token Account
  await setAuthority(
    connection, // Connection to use
    payer, // Payer of the transaction fee
    tokenAccount, // Token Account
    payer.publicKey, // Owner of the Token Account
    AuthorityType.AccountOwner, // Type of Authority
    new Keypair().publicKey, // New Account Owner
    undefined, // Additional signers
    undefined, // Confirmation options
    TOKEN_2022_PROGRAM_ID, // Token Extension Program ID
  );
} catch (error) {
  console.log("\nExpect Error:", error);
}

Conclusion

The ImmutableOwner extension prevents a vulnerability that was previously possible by reassigning the owner of Associated Token Accounts. This security feature can also be applied to any new Token Account, guarding against unintended ownership changes.

How to use the Immutable Owner extension

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