YubiKit Core Module

This module contains the base library, with common definitions and utilities used throughout the rest of the modules. This module is typically not used alone, but as a dependency of the other modules. For example, see the Android module which contains implementations for the interfaces defined in this module.


You typically don’t have to depend on this module explicitly, as it will be pulled in as a dependency to other modules.

To add the Core module as a dependency to your project, add the following to your gradle configuration:

dependencies {
  implementation 'com.yubico.yubikit:core:(insert version here)'

Core interfaces


This class represents a YubiKey, connected over a transport, such as USB or NFC. To use it, create a connection to transmit data to it. See the Android module for how to get a reference to a YubiKeyDevice.


There may be several types of connections available, depending on the transport used. This module defines three types: SmartCardConnection, OtpConnection, and FidoConnection. Only one connection may be open at a time.


This represents an open session with an application on a YubiKey. Subclasses handling a specific application are available in the various application modules

Raw smart card communication (APDUs)

While using the higher-level abstractions for the YubiKey applications provided as separate modules is generally recommended, it is possible to communicate with a YubiKey over a lower-level "smart card like" interface. This modules provides a SmartCardProtocol helper class for that purpose, which will handle protocol details like APDU encoding and chaining:

// Connect to the YubiKey / start the connection
device.requestConnection(SmartCardConnection.class, result -> {
  // The result is a Result<SmartCardConnection, IOException>, which represents either a successful connection, or an error.
  try {
    SmartCardConnection connection = result.getValue();  // This may throw an IOException
    // The SmartCardProtocol offers a the ability of sending APDU-based smartcard commands
    SmartCardProtocol protocol = new SmartCardProtocol(connection);
    byte[] aid = new byte[] {0xA0, 0x00, 0x00, 0x03, 0x08};
    protocol.select(aid);  // Select a smartcard application (this may throw an ApplicationNotAvailableException)
    try {
      // Send a command
      byte[] response = protocol.sendAndReceive(new Apdu(0x00, 0xA4, 0x00, 0x00)));
      // Response contains the response payload, if the command was successful.
    } catch(ApduException e) {
      // The response was an error, e.getSw() contains the status code.
  } catch(ApplicationNotAvailableException | IOException e) {
    // Handle errors