Create passkey accounts

Prerequisites:

• @category-labs/mera installed.
• A PRF-capable authenticator (authenticator support).

Create the passkey

import { createPasskeyWithPrfOutput } from "@category-labs/mera";

const rpId = location.hostname;

const created = await createPasskeyWithPrfOutput({
  rp: { id: rpId, name: "Example" },
  user: { name: "account@example.com", displayName: "Example account" },
});

Every call creates a new passkey.

Remember the credential

The app can store the credential metadata and pass it back on the next sign-in, so the browser reuses the same passkey instead of offering a choice.

localStorage.setItem(
  "app.derivedCredential",
  JSON.stringify({
    credentialId: created.credentialId,
    transports: created.transports,
  }),
);

transports is optional and only a hint: the browser uses it to reach the authenticator directly (a platform prompt for a platform passkey, a QR flow for a phone) instead of offering every option.

Sign in

import { getPasskeyPrfOutput } from "@category-labs/mera";

const stored = localStorage.getItem("app.derivedCredential");
const known = stored ? JSON.parse(stored) : undefined;

const { prfOutput, credentialId } = await getPasskeyPrfOutput({
  rpId,
  credential: known,
});

// With no stored record, the browser may have used any discoverable passkey.
const record =
  known?.credentialId === credentialId ? known : { credentialId };
localStorage.setItem("app.derivedCredential", JSON.stringify(record));

Offer one button

On a visit with no stored record, a single “Continue with passkey” button can sign in when the device holds a passkey and offer the other paths when it does not. immediate asks only for passkeys already on this device and rejects at once, with no prompt, when there is none:

import { getPasskeyPrfOutput, MeraError } from "@category-labs/mera";

async function signInOnThisDevice(): Promise<Uint8Array | undefined> {
  try {
    const { prfOutput, credentialId } = await getPasskeyPrfOutput({
      rpId,
      immediate: true,
    });
    localStorage.setItem(
      "app.derivedCredential",
      JSON.stringify({ credentialId }),
    );
    return prfOutput;
  } catch (error) {
    if (
      !(error instanceof MeraError) ||
      error.code !== "PASSKEY_CANCELLED"
    ) {
      throw error;
    }
    return undefined;
  }
}

const prfOutput = await signInOnThisDevice();

The trade-off: immediate skips passkeys on other devices, so a person whose passkey is on their phone gets undefined too. When prfOutput is undefined, the app offers “Create a passkey” and “Use a passkey from another device”, a sign-in without immediate. Browsers without immediate mode ignore the option and show their usual prompt.

Derive numbered accounts

deriveEvmPrivateKey and deriveSolanaPrivateKey number accounts by accountIndex. These helpers open one account of each kind:

import {
  createEd25519SigningSession,
  createSecp256k1SigningSession,
  deriveEvmPrivateKey,
  deriveSolanaPrivateKey,
  getEvmAddress,
  getSolanaAddress,
} from "@category-labs/mera";

function openEvmAccount(prfOutput: Uint8Array, accountIndex: number) {
  const privateKey = deriveEvmPrivateKey({ prfOutput, accountIndex });
  const session = createSecp256k1SigningSession({ privateKey });
  privateKey.fill(0);
  return { session, address: getEvmAddress(session.publicKey) };
}

function openSolanaAccount(prfOutput: Uint8Array, accountIndex: number) {
  const privateKey = deriveSolanaPrivateKey({ prfOutput, accountIndex });
  const session = createEd25519SigningSession({ privateKey });
  privateKey.fill(0);
  return { session, address: getSolanaAddress(session.publicKey) };
}

Each session copies the key, so the helpers zero the derived key right away.

Build the account list from these helpers. The PRF output reproduces every account, so it is zeroed once they are open:

const accounts = [
  openEvmAccount(prfOutput, 0),
  openSolanaAccount(prfOutput, 0),
];
prfOutput.fill(0);

End the sessions

for (const account of accounts) {
  account.session.end();
}

Ending a session zeroes the private keys it owns.

See also

• Passkey accounts: the account model this recipe implements.
• Send a transaction with viem: sign and broadcast with a derived account.
• createPasskeyWithPrfOutput and getPasskeyPrfOutput: the two ceremonies this recipe runs.
• deriveEvmPrivateKey and deriveSolanaPrivateKey: the derivation paths and their @scure equivalents.
• React and Vue web demos: full browser apps that follow this recipe for one EVM account.