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FIDO2 CTAP2 Javacard Applet

Overview

This repository contains sources for a feature-rich, FIDO2 CTAP2.1 compatible applet targeting the Javacard Classic system, version 3.0.4. In a nutshell, this lets you take a smartcard, install an app onto it, and have it work as a FIDO2 authenticator device with a variety of features. You can generate and use OpenSSH ecdsa-sk type keys, including ones you carry with you on the key (-O resident). You can securely unlock a LUKS encrypted disk with systemd-cryptenroll. You can log in to a Linux system locally with pam-u2f.

100% of the FIDO2 CTAP2.1 spec is covered, with the exception of features that aren't physically on an ordinary smartcard, such as biometrics or other on-board user verification. The implementation in the default configuration passes the official FIDO certification test suite version 1.7.17 in "CTAP2.1 full feature profile" mode.

In order to run this outside a simulator, you will need a compatible smartcard. Some smartcards which describe themselves as running Javacard 3.0.1 also work - see the detailed requirements.

You might be interested in reading about the security model.

Environment Setup and Building the application

1. Download JavacardKit: Obtain a copy of JavacardKit version 3.0.4 (or jckit_303 if you prefer).

2. Set Environment Variable: Configure the JC_HOME environment variable to point to your JavacardKit directory.

   export JC_HOME=<path_to_your_jckit_directory>
   

3. Run Gradle Build: Execute the following command to build the JavaCard application, which will produce a .cap file for installation.

   ./gradlew buildJavaCard
   

Testing the Application

Overview

You have multiple options for testing the JavaCard application:

1. Actual Smartcard: You can test on a physical smartcard.
2. Virtual SmartCard: Alternatively, you can use VSmartCard and JCardSim for quicker and easier testing.

Detailed Steps

Option 1: Using Actual Smartcard

Simply install the .cap file onto the smartcard and proceed with testing.

Option 2: Using Virtual SmartCard and JCardSim

1. VSmartCard and JCardSim: Use these tools for a simulated environment.
2. Third-Party Testing Suites: Utilize tools like SoloKey's fido2-tests for comprehensive analysis. The VSim class can help you get started.

Python Tests

1. Python Test Suite: Navigate to the python_tests directory, which contains Python-language tests.
2. Run the Tests: Execute the following commands to set up and run the tests.

   export JC_HOME=<your_jckit>
   ./gradlew jar testJar
   python -m venv venv
   ./venv/bin/pip install -U -r requirements.txt
   ./venv/bin/python -m unittest discover -s python_tests
   

3. Interoperability: These tests use the Python python-fido2 library because there is currently no FIDO2 client library for the JVM. You can also test with libfido2, Python libraries, or the official FIDO Standards Tests (Javascript).

Advanced Settings

• Fast IPC: By default, the tests use fast interprocess communication with the JVM, bypassing PC/SC. The tests take less than fifteen seconds to run, for me, even though there are almost two hundred cases.
• Customization: You can modify settings in python_tests/ctap/ctap_test.py to enable CTAP traffic logging, allow JVM remote debugging, or use a VSmartCard PC/SC connection.

Contributing

• If you wish to contribute to the project, feel free to raise a pull request or open an issue.

Where to go Next

If you just want to install the app, look at what you can configure.

I suggest reading the FAQ and perhaps the security model.

If you're a really detail-oriented person, you might enjoy reading about the implementation.

Implementation Status

Software Compatibility

There are two compatibility issues in the table above:

1. Google Play Services on Android contains a complete webauthn implementation, but it appears to be hardwired to use only "passkeys". If a site explicitly requests a non-discoverable credential, you will be prompted to use an NFC security key, but this is only CTAP1 and not CTAP2. There's nothing fundamentally preventing this from working on Android but the current state of Chrome and Fennec are that CTAP2 doesn't, because both use the broken Play Services library. MicroG has a fully-working implementation, though! See https://github.com/microg/GmsCore/pull/2194 for PIN support.
2. Some browsers support FIDO2 in theory but only allow USB security keys - this implementation is for PC/SC, and doesn't implement USB HID, so it will only work with FIDO2 implementations that can handle e.g. NFC tokens instead of being restricted to USB. In order to use a smartcard in these situations you'll need https://github.com/StarGate01/CTAP-bridge , https://github.com/BryanJacobs/fido2-hid-bridge/ , https://github.com/BryanJacobs/FIDOk/ or similar, bridging USB-HID traffic to PC/SC.