Add Accounts to the SDK

Add accounts with the account (viewing/privacy) key.

Because all notes representing value on Aztec network are encrypted, the SDK requires access to a user's account key in order to decrypt the notes and calculate the account balance.

Please review the page on Accounts if you haven't already as it will help you understand the difference between Ethereum and Aztec accounts.

Aztec will support the same elliptic curve as Ethereum in the future so Ethereum accounts will be Aztec accounts.

Account Keys

Privacy keys can be any random 32 bytes. The SDK allows you to generate keys deterministically from Ethereum accounts by deriving Aztec keys from signed Ethereum messages.

Generate

You can generate the account key from an Ethereum private key by signing this message:

Sign this message to generate your Aztec Privacy Key. This key lets the application decrypt your balance on Aztec.\n\nIMPORTANT: Only sign this message if you trust the application.

and taking the first 32 bytes of the resulting signed message. You can find an example in the SDK here.

const { publicKey, privateKey } = sdk.generateAccountKeyPair(ethereumAccount);

Add to SDK

With the account key, adding the user to the SDK is as simple as passing the key and the nonce for the account.

const account = await sdk.addUser(accountKey);

Read

Now just make sure the SDK account has synced and you can read account balances:

await account.awaitSynchronised();
const zkEthBalance = await account.getBalance(sdk.getAssetIdBySymbol("ETH"));

Spending Keys

Once a spending key has been registered, either the account key or a registered spending key can be used to spend notes. This creates a useful separation between account (or "viewing/privacy keys") and spending keys. The sender of a note can specify whether the note is spendable by the account key or a registered spending key. This is specified with the recipientSpendingKeyRequired flag when setting up a controller. See the TransferController for an example.

It is considered best practice to register a new spending key as soon as possible. You can read more about registering new accounts for users on the Register Users page. Here, we will briefly review how to add a spending key to the SDK that has already been registered.

You can create an Aztec signer by passing the signing key to the createSchnorrSigner(privateKey: Buffer) method. It returns a signer that you can pass to various Controllers to sign transactions on the network on behalf of the account.

const signer = await sdk.createSchnorrSigner(signingPrivateKey);

Like account keys, spending keys can be 32 random bytes, but the SDK allows you to generate them deterministically from Ethereum accounts by deriving them from a signed message. The message used for creating signing keys is:

Sign this message to generate your Aztec Spending Key. This key lets the application spend your funds on Aztec.\n\nIMPORTANT: Only sign this message if you trust the application.

You can see an example in the SDK source code here.

Add User

sdk.addUser(accountPrivateKey: Buffer, noSync?: boolean): Promise<AztecSdkUser>;

Get User

sdk.getUser(userId: GrumpkinAddress): Promise<AztecSdkUser>;