Key Gateway

The Key Gateway adds new keys to the Key Registry.

If you want to add a new public key to a Farcaster account, use the Key Gateway.

Read

nonces

Returns the next available nonce for an address. Used for generating EIP-712 signatures in addFor.

Parameter	type	Description
owner	address	The address to query the nonce for

Write

add

Add a new key for the caller's fid and set its state to Added. Revert if the key is already registered.

Parameter	type	Description
keyType	uint32	Must be set to 1. This is currently the only supported keyType.
key	bytes	The public key to add
metadataType	uint8	Must be set to 1. This is currenlty the only supported metadataType.
metadata	bytes	Encoded SignedKeyRequestMetadata

addFor

Add a key on behalf of another fid by providing a signature. The owner must sign an EIP-712 Add message approving the key. Reverts if the key is already registered.

Parameter	type	Description
fidOwner	address	Address of the fid owner
keyType	uint32	Must be set to 1. This is currently the only supported keyType.
key	bytes	The public key to add
metadataType	uint8	Must be set to 1. This is currenlty the only supported metadataType.
metadata	bytes	Encoded SignedKeyRequestMetadata
deadline	uint256	Signature expiration timestamp
sig	bytes	EIP-712 Add signature from fidOwner

Add signature

To add a key on behalf of another account, you must provide an EIP-712 typed signature from the account in the following format:

Add(address owner,uint32 keyType,bytes key,uint8 metadataType,bytes metadata,uint256 nonce,uint256 deadline)

Parameter	type	Description
owner	address	Address that owns the fid. The typed message must be signed by this address.
keyType	uint32	Must be set to 1. This is currently the only supported keyType.
key	bytes	The public key to add
metadataType	uint8	Must be set to 1. This is currenlty the only supported metadataType.
metadata	bytes	Encoded SignedKeyRequestMetadata
nonce	uint256	Current nonce of the owner address
deadline	uint256	Signature expiration timestamp

@farcaster/hub-web

import { ViemWalletEip712Signer } from '@farcaster/hub-web';
import { walletClient, account } from './clients.ts';
import { getPublicKey } from './signer.ts';
import { readNonce, getDeadline } from './helpers.ts';

const publicKey = await getPublicKey();
const metadata = await getMetadata();
const nonce = await readNonce();
const deadline = getDeadline();

const eip712Signer = new ViemWalletEip712Signer(walletClient);
const signature = await eip712signer.signAdd({
  owner: account,
  keyType: 1,
  key: publicKey,
  metadataType: 1,
  metadata,
  nonce,
  deadline,
});

Viem

import { KEY_GATEWAY_EIP_712_TYPES } from '@farcaster/hub-web';
import { bytesToHex } from 'viem';
import { walletClient, account } from './clients.ts';
import { getPublicKey } from './signer.ts';
import { getMetadata } from './metadata.ts';
import { readNonce, getDeadline } from './helpers.ts';

const publicKey = await getPublicKey();
const metadata = await getMetadata();
const nonce = await readNonce();
const deadline = getDeadline();

const signature = await walletClient.signTypedData({
  account,
  ...KEY_GATEWAY_EIP_712_TYPES,
  primaryType: 'Add',
  message: {
    owner: account,
    keyType: 1,
    key: bytesToHex(publicKey),
    metadataType: 1,
    metadata,
    nonce,
    deadline,
  },
});

helpers.ts

import { KEY_GATEWAY_ADDRESS, keyGatewayABI } from '@farcaster/hub-web';
import { publicClient, account } from './clients.ts';

export const getDeadline = () => {
  const now = Math.floor(Date.now() / 1000);
  const oneHour = 60 * 60;
  return now + oneHour;
};

export const readNonce = async () => {
  return await publicClient.readContract({
    address: KEY_GATEWAY_ADDRESS,
    abi: keyGatewayABI,
    functionName: 'nonces',
    args: [account],
  });
};

metadata.ts

import { ViemLocalEip712Signer } from '@farcaster/hub-web';
import { privateKeyToAccount } from 'viem/accounts';
import { getDeadline } from './helpers.ts';
import { getPublicKey } from './signer.ts';

// App account
export const appAccount = privateKeyToAccount('0x...');

const deadline = getDeadline();
const publicKey = await getPublicKey();

export const getMetadata = async () => {
  const eip712signer = new ViemLocalEip712Signer(appAccount);
  const metadata = await eip712signer.getSignedKeyRequestMetadata({
    requestFid: 9152n, // App fid
    key: publicKey,
    deadline,
  });
  if (metadata.isOk()) {
    return metadata.value;
  }
};

signer.ts

import * as ed from '@noble/ed25519';
import { NobleEd25519Signer } from '@farcaster/hub-web';

const privateKeyBytes = ed.utils.randomPrivateKey();
export const accountKey = new NobleEd25519Signer(privateKeyBytes);

export const getPublicKey = async () => {
  const accountKeyResult = await accountKey.getSignerKey();
  if (accountKeyResult.isOk()) {
    return accountKeyResult.value;
  }
};

clients.ts

import { createWalletClient, createPublicClient, custom, http } from 'viem';
import { privateKeyToAccount } from 'viem/accounts';
import { optimism } from 'viem/chains';

export const publicClient = createPublicClient({
  chain: optimism,
  transport: http(),
});

export const walletClient = createWalletClient({
  chain: optimism,
  transport: custom(window.ethereum),
});

// JSON-RPC Account
export const [account] = await walletClient.getAddresses();

// Local Account
export const account = privateKeyToAccount('0x...');

Errors

Error	Selector	Description
InvalidMetadata	bcecb64a	The signed metadata provided with the key is invalid.
InvalidSignature	8baa579f	The provided signature is invalid. It may be incorrectly formatted, or signed by the wrong address.
SignatureExpired	0819bdcd	The provided signature has expired. Collect a new signature from the signer with a later deadline timestamp.

Source

KeyGateway.sol