OBSOLETE: This project is no longer maintained. U2F has been superseded by Web Authentication, and this project is superseded by java-webauthn-server. We recommend using WebAuthn instead.

Server-side U2F library for Java. Provides functionality for registering U2F devices and authenticating with said devices.

Migrating to WebAuthn

See the Migrating from U2F section in the java-webauthn-server documentation.





repositories{ mavenCentral() }
dependencies {
  compile 'com.yubico:u2flib-server-core:0.19.12'

Example Usage

Make sure that you have read Using a U2F library before continuing.
private abstract Iterable<DeviceRegistration> getRegistrations(String username);

public View startAuthentication(String username) throws NoEligibleDevicesException {

    // Generate a challenge for each U2F device that this user has registered
    SignRequestData requestData
        = u2f.startSignature(SERVER_ADDRESS, getRegistrations(username));

    // Store the challenges for future reference
    requestStorage.put(requestData.getRequestId(), requestData.toJson());

    // Return an HTML page containing the challenges
    return new AuthenticationView(requestData.toJson(), username);

public String finishAuthentication(SignResponse response, String username) throws
        DeviceCompromisedException {

    // Get the challenges that we stored when starting the authentication
    SignRequestData signRequest
        = requestStorage.remove(response.getRequestId());

    // Verify the that the given response is valid for one of the registered devices

    return "Successfully authenticated!";

In the above example getRegistrations() will return the U2F devices currently associated with a given user. This is most likely stored in a database. See u2flib-server-demo for a complete demo server (including registration and storage of U2F devices).



The attestation module (u2flib-server-attestation) enables you to restrict registrations to certain U2F devices (e.g. devices made by a specific vendor). It can also provide metadata for devices.


All relevant classes implement Serializable, so instead of using toJson(), you can use Java’s built in serialization mechanism. Internally the classes use Jackson to serialize to and from JSON, and the ObjectMapper from Jackson can be used.