OTPAuth

One Time Password library for Node.js, Deno, Bun and browsers.

It supports the generation and validation of HMAC-Based One-Time Passwords (HOTP) as specified in RFC 4226 and Time-Based One-Time Passwords (TOTP) as specified in RFC 6238. Frequently used in Multi-Factor Authentication (MFA) / Two-Factor Authentication (2FA) systems.

[!TIP] You can try the library with the demo application available at otpauth.molinero.dev.

If you wish to interact with the library in your browser console, the following snippet can be used:

const OTPAuth = await import("otpauth");

Usage

This section presents an overview of the most common usage patterns, along with some security recommendations.

Node.js / Bun

import * as OTPAuth from "otpauth";
// import * as OTPAuth from "otpauth/slim"; // Slim build without bundled dependencies.
// import * as OTPAuth from "otpauth/bare"; // Bare build with no bundled crypto (requires providing a custom HMAC function).

// Create a new TOTP object.
let totp = new OTPAuth.TOTP({
  // Provider or service the account is associated with.
  issuer: "ACME",
  // Account identifier.
  label: "Alice",
  // Algorithm used for the HMAC function, possible values are:
  //   "SHA1", "SHA224", "SHA256", "SHA384", "SHA512",
  //   "SHA3-224", "SHA3-256", "SHA3-384" and "SHA3-512".
  algorithm: "SHA1",
  // Length of the generated tokens.
  digits: 6,
  // Interval of time for which a token is valid, in seconds.
  period: 30,
  // Arbitrary key encoded in base32 or `OTPAuth.Secret` instance
  // (if omitted, a cryptographically secure random secret is generated).
  secret: "US3WHSG7X5KAPV27VANWKQHF3SH3HULL",
  //   or: `OTPAuth.Secret.fromBase32("US3WHSG7X5KAPV27VANWKQHF3SH3HULL")`
  //   or: `new OTPAuth.Secret()`
  // Custom HMAC function (required for bare build, optional otherwise).
  // hmac: (algorithm, key, message) => Uint8Array,
});

// Unless you know what you are doing, it is recommended to use the default
// values for the algorithm, digits, and period options, as these are the most
// common values used by most services.

// Generate a cryptographically secure random secret.
// It is NOT recommended to use less than 128 bits (16 bytes).
let secret = new OTPAuth.Secret({ size: 20 });

// Generate a token (returns the current token as a string).
let token = totp.generate();

// Get the counter value (number of intervals since the Unix epoch).
let timestamp = Date.now();
let counter = totp.counter({ timestamp });

// Validate a token (returns the token delta or null if it is not found in the
// search window, in which case it should be considered invalid). Since a valid
// token can return 0 and null is coerced to 0 in comparisons, always check
// `delta !== null` explicitly.
//
// A search window is useful to account for clock drift between the client and
// server; however, it should be kept as small as possible to prevent brute
// force attacks. In most cases, a value of 1 is sufficient. Furthermore, it is
// essential to implement a throttling mechanism on the server.
//
// For further details on the security considerations, it is advised to refer
// to Section 7 of RFC 4226 and Section 5 of RFC 6238:
//   https://datatracker.ietf.org/doc/html/rfc4226#section-7
//   https://datatracker.ietf.org/doc/html/rfc6238#section-5
let delta = totp.validate({ token, window: 1 });

// Alternatively, to prevent token reuse, pass the counter of the last accepted
// token as `afterCounter` and use the same timestamp as `counter`.
let lastCounter = null; // Persisted by the application (null if none).
delta = totp.validate({ token, timestamp, window: 1, afterCounter: lastCounter });
if (delta !== null) lastCounter = counter + delta;

// Get the remaining milliseconds until the current token changes.
let remaining = totp.remaining();

// Convert to Google Authenticator key URI format.
// Usually the URI is encoded in a QR code that can be scanned by the user.
// This functionality is outside the scope of the project, but there are many
// libraries that can be used for this purpose, such as npmjs.com/package/qr
let uri = totp.toString();
//   or:      `OTPAuth.URI.stringify(totp)`
//   returns: `otpauth://totp/ACME:Alice?issuer=ACME&secret=US3WHSG7X5KAPV27VANWKQHF3SH3HULL&algorithm=SHA1&digits=6&period=30`

// Convert from Google Authenticator key URI format.
totp = OTPAuth.URI.parse(uri);

Deno

import * as OTPAuth from "jsr:@hectorm/otpauth";

// Same as above.

Browsers (ESM)

<script type="importmap">
  {
    "imports": { "otpauth": "https://cdn.jsdelivr.net/npm/otpauth@%VERSION%/dist/otpauth.esm.min.js" },
    "integrity": { "https://cdn.jsdelivr.net/npm/otpauth@%VERSION%/dist/otpauth.esm.min.js": "%HASH%" }
  }
</script>
<script type="module">
  import * as OTPAuth from "otpauth";

  // Same as above.
</script>

Browsers (UMD)

<script
  src="https://cdn.jsdelivr.net/npm/otpauth@%VERSION%/dist/otpauth.umd.min.js"
  integrity="%HASH%"
  crossorigin="anonymous"
  referrerpolicy="no-referrer"
></script>
<script>
  // Same as above.
</script>

Documentation

For additional information, please refer to the documentation page at hectorm.github.io/otpauth/.

License

MIT License © Héctor Molinero Fernández.