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FIDO2 Javacard Applet

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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](https://github.com/Yubico/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. Some CTAP 2.2+ features are also supported.

In order to run this outside a simulator, you will need
[a compatible smartcard](docs/requirements.md). 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](docs/security_model.md).

## Environment setup and building the application

1. Configure the `JC_HOME` environment variable to point to a JavacardKit directory (optionally from the `sdks` submodule of this repository).
   ```bash
   export JC_HOME=<path_to_your_jckit_directory>
   ```

2. Build the JavaCard application, producing a `.cap` file for installation in `build/javacard`.
    ```bash
   ./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**: You can use VSmartCard and JCardSim for quicker and easier testing.

### Detailed Steps for Virtual Testing

When running through VSmartCard and JCardSim, you can use
tools like SoloKey's `fido2-tests` or other test suites.
The `VSim` class in this repository might help you get started.

#### Python Tests

Navigate to the `python_tests` directory, which contains Python-language tests, and:

```bash
   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
   ```

These tests use the Python `python-fido2` library because there 
was, before FIDOk at the time this app was written, no FIDO2 client library
for the JVM. You can also test with `libfido2`, Python libraries, or the
official FIDO Standards Tests (Javascript).

By default, the Python tests use fast interprocess communication with the JVM,
bypassing PC/SC. The tests take less than thirty seconds to run, for me, even
though there are almost two hundred cases.

#### Advanced Settings

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 instead of the default IPC.

## 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](docs/installation.md).

I suggest [reading the FAQ](docs/FAQ.md) and perhaps [the security model](docs/security_model.md).

If you're a really detail-oriented person, you might enjoy reading
[about the implementation](docs/implementation.md).

## Implementation Status

| Feature                             | Status                                                |
|-------------------------------------|-------------------------------------------------------|
| CTAP1/U2F                           | Implemented (see [install guide](docs/certs.md))      |
| CTAP2.0 core                        | Implemented                                           |
| CTAP2.1 core                        | Implemented                                           |
| Resident keys / Discoverable creds  | Implemented                                           |
| User Presence                       | User always considered present: one verification only |
| ECDSA (SecP256r1)                   | Implemented                                           |
| Other crypto, like ed25519          | Not implemented - availability depends on hardware    |
| Self attestation                    | Implemented                                           |
| Basic attestation with ECDSA certs  | Implemented (see [install guide](docs/certs.md))      |
| Webauthn (NOT CTAP!) uvm extension  | Implemented                                           |
| Webauthn devicePubKey extension     | Not implemented                                       |
| CTAP2.1 hmac-secret extension       | Implemented                                           |
| CTAP2.2 hmac-secret-mc extension    | Not implemented                                       |
| CTAP2.1 alwaysUv option             | Implemented                                           |
| CTAP2.1 credProtect option          | Implemented                                           |
| CTAP2.1 PIN Protocol 1              | Implemented                                           |
| CTAP2.1 PIN Protocol 2              | Implemented                                           |
| CTAP2.1 credential management       | Implemented                                           |
| CTAP2.1 enterprise attestation      | Implemented in code, disabled                         |
| CTAP2.1 PIN complexity policies     | Not implemented (min length is supported though)      |
| CTAP2.1 authenticator config        | Implemented                                           |
| CTAP2.1 minPinLength extension      | Implemented, default max two RPIDs can receive        |
| CTAP2.1 credBlob extension          | Implemented, discoverable creds only                  |
| CTAP2.1 largeBlobKey extension      | Implemented                                           |
| CTAP2.1 authenticatorLargeBlobs     | Implemented, default 1024 bytes storage (max 4k)      |
| CTAP2.1 bio-stuff                   | Not implemented (doesn't make sense in this context?) |
| CTAP2.2 thirdPartyPayment extension | Not implemented                                       |
| CTAP2.2 persistent UV token         | Not implemented                                       |
| CTAP2.2 encIdentifier               | Not implemented                                       |
| CTAP2.2 uvCountSinceLastPinEntry    | Not implemented                                       |
| CTAP2.3 long touch for reset        | Not implemented (doesn't make sense in this context)  |
| CTAP2.2/2.3 hybrid authenticator    | Not implemented (doesn't make sense in this context)  |
| Key backups                         | Not implemented                                       |
| APDU chaining                       | Supported                                             |
| Extended APDUs                      | Supported                                             |
| Performance                         | Adequate (sub-3-second common operations)             |
| Resource consumption                | Reasonably optimized for avoiding flash wear          |
| Bugs                                | Probably? Many have been fixed. Appears to work OK.   |
| Code quality                        | No                                                    |
| Security                            | Theoretical, but see "bugs" row above                 |

## Software Compatibility

| Platform                  | Status           |
|---------------------------|------------------|
| Android (Google Play)     | CTAP1 only [1]   |
| Android (hwsecurity)      | Working          |
| Android (MicroG)          | Working          |
| Android (FIDOk)           | Working          |
| iOS                       | Reported working |
| Linux (libfido2)          | Working          |
| Linux (FIDOk)             | Working          |
| Windows 10                | Working          |

| Smartcard                                                                         | Status           |
|-----------------------------------------------------------------------------------|------------------|
| J3H145 (NXP JCOP3)                                                                | Working          |
| J3R180 (NXP JCOP4)                                                                | Working          |
| OMNI Ring (Infineon SLE78)                                                        | Working          |
| jCardSim                                                                          | Working          |
| [Vivokey FlexSecure (NXP JCOP4)](https://dangerousthings.com/product/flexsecure/) | Working          |
| A40CR                                                                             | Reported Working |

| Application         | Status                         |
|---------------------|--------------------------------|
| Chrome on Android   | Working [1]                    |
| Chrome on Linux     | Working, USBHID only [2]       |
| Chrome on Windows   | Working                        |
| Fennec on Android   | Working (Play Services [1])    |
| WebView on Android  | Working                        |
| Firefox on Linux    | Working, USBHID only [2]       |
| Firefox on Windows  | Working                        |
| MS Edge on Windows  | Working                        |
| Safari on iOS       | Reported working               |
| OpenSSH             | Working                        |
| pam_u2f             | Working                        |
| systemd-cryptenroll | Working                        |
| python-fido2        | Working                        |
| FIDOk               | Working                        |

There are two compatibility issues in the table above:
1. Since the Google Play Services update v26.03 of January 2026, NFC FIDO2 authenticators with
   resident credentials and PIN verification are supported for Android 9 and later.
   The Google Play Services do require the applet to be installed with the `CardReset` privilege
   as described in [the installation manual](docs/installation.md).

The system UI still does not allow for changing PIN or deleting credentials, for that you will
   need an application such as [Authnkey](https://github.com/mimi89999/Authnkey)
   ([F-Droid](https://f-droid.org/packages/pl.lebihan.authnkey/)
   / [Google Play](https://f-droid.org/packages/pl.lebihan.authnkey/)).

Previously, the Google Play Services only supported CTAP1 over the NFC transport which was
   restricted to the creation of *non-discoverable* credentials for second-factor authentication.
   MicroG already had 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.

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