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U2F authentication library

This is a simple library to register and check signatures provided by U2F clients/devices. It's intended to be used in Relying Parties - websites that want to add U2F 2-factor authentication for their users.

To use U2F, it is recommended to familiarize yourself with FIDO Alliance Specifications, although basic usage is shown below.

U2F Overview/properties

  • U2F provides hardware-based 2-nd factor authentication system. Public/private key infrastructure is used to ensure good security.
  • Provides proof of posession of hardware key, plus user presence flag.
  • Public/private key pairs are specific to website origin and 'application id'. Keys are useless if used from other origins.
  • Needs to be stored on server for each user: Key handle and public key (both strings).
  • Cannot be used as main authentication system because server needs to provide unique key handle to the user to get the signature.

Basic usage

User Registration Flow

// 1. Check that the user is logged in.

// 2. (On server) generate user registration request and save it in session:
var u2f = require('u2f');

var req = u2f.request("<appId>");
session.authRequest = req;

// 3. Send req to the client and use U2F API to request registration, then send result back.
// (On client)  u2f.register([req], [], function(res) { /* send res back to server */ })

// 4. (Server) Check registration result.
var checkres = u2f.checkRegistration(session.authRequest, res);

if (checkres.successful) {
    // Registration successful, save 
    // checkres.keyHandle and checkres.publicKey to user's account in your db.
} else {
    // checkres.errorMessage will contain error text.
}

User Authentication Flow

// 1. Check that the user is logged in using password authentication (or some other way).

// 2. (On server) generate user sign request using keyHandle from user account.
var req = u2f.request("<appId>", user.keyHandle);
session.authRequest = req;

// 3. (On client) use U2F API to request signature.
// u2f.sign([req], function(res) { /* send res back to server */ });

// 4. (On server) check signature using publicKey from user account.
var checkres = u2f.checkSignature(session.authRequest, res, user.publicKey);

if (checkres.successful) {
    // User is authenticated.
} else {
    // checkres.errorMessage will contain error text.
}

Useful links

http://demo.yubico.com/u2f
https://github.com/Yubico/python-u2flib-server

TODO

  • Provide instructions for client-side. How to get the 'u2f' namespace, what browsers are supported.
  • Change API to enable multiple keyhandle/publickey pairs for a single user.
  • Unpack registration certificate and check its own signature and time constraints.

License

MIT