OpenSK

This repository contains a Rust implementation of a FIDO2 authenticator.

We developed this as a Tock OS application and it has been successfully tested on the following boards:

• Nordic nRF52840-DK
• Nordic nRF52840-dongle

Disclaimer

This project is proof-of-concept and a research platform. It is NOT meant for a daily usage. It's still under development and as such comes with a few limitations:

FIDO2

Although we tested and implemented our firmware based on the published CTAP2.0 specifications, our implementation was not reviewed nor officially tested and doesn't claim to be FIDO Certified. We started adding features of the upcoming next version of the CTAP2.1 specifications. The development is currently between 2.0 and 2.1, with updates hidden behind a feature flag. Please add the flag --ctap2.1 to the deploy command to include them.

Cryptography

We're currently still in the process on making the ARM® CryptoCell-310 embedded in the Nordic nRF52840 chip work to get hardware-accelerated cryptography. In the meantime we implemented the required cryptography algorithms (ECDSA, ECC secp256r1, HMAC-SHA256 and AES256) in Rust as a placeholder. Those implementations are research-quality code and haven't been reviewed. They don't provide constant-time guarantees and are not designed to be resistant against side-channel attacks.

Installation

For a more detailed guide, please refer to our installation guide.

1. If you just cloned this repository, run the following script (Note: you only need to do this once):

   ./setup.sh

2. Next step is to install Tock OS as well as the OpenSK application on your board (Warning: it will erase the locally stored credentials). Run:

   # Nordic nRF52840-DK board
   ./deploy.py --board=nrf52840dk --opensk
   # Nordic nRF52840-Dongle
   ./deploy.py --board=nrf52840_dongle --opensk

3. On Linux, you may want to avoid the need for root privileges to interact with the key. For that purpose we provide a udev rule file that can be installed with the following command:

   sudo cp rules.d/55-opensk.rules /etc/udev/rules.d/ &&
   sudo udevadm control --reload

Customization

If you build your own security key, depending on the hardware you use, there are a few things you can personalize:

1. If you have multiple buttons, choose the buttons responsible for user presence in main.rs.
2. Decide whether you want to use batch attestation. There is a boolean flag in ctap/mod.rs. It is mandatory for U2F, and you can create your own self-signed certificate. The flag is used for FIDO2 and has some privacy implications. Please check WebAuthn for more information.
3. Decide whether you want to use signature counters. Currently, only global signature counters are implemented, as they are the default option for U2F. The flag in ctap/mod.rs only turns them off for FIDO2. The most privacy preserving solution is individual or no signature counters. Again, please check WebAuthn for documentation.
4. Depending on your available flash storage, choose an appropriate maximum number of supported residential keys and number of pages in ctap/storage.rs.
5. Change the default level for the credProtect extension in ctap/mod.rs. When changing the default, resident credentials become undiscoverable without user verification. This helps privacy, but can make usage less comfortable for credentials that need less protection.
6. Increase the default minimum length for PINs in ctap/storage.rs. The current minimum is 4. Values from 4 to 63 are allowed. Requiring longer PINs can help establish trust between users and relying parties. It makes user verification harder to break, but less convenient. NIST recommends at least 6-digit PINs in section 5.1.9.1: https://pages.nist.gov/800-63-3/sp800-63b.html You can add relying parties to the list of readers of the minimum PIN length.

3D printed enclosure

To protect and carry your key, we partnered with a professional designer and we are providing a custom enclosure that can be printed on both professional 3D printers and hobbyist models.

All the required files can be downloaded from Thingiverse including the STEP file, allowing you to easily make the modifications you need to further customize it.

Development and testing

Printing panic messages to the console

By default, libtock-rs blinks some LEDs when the userspace application panicks. This is not always convenient as the panic message is lost. In order to enable a custom panic handler that first writes the panic message via Tock's console driver, before faulting the app, you can use the --panic-console flag of the deploy.py script.

# Example on Nordic nRF52840-DK board
./deploy.py --board=nrf52840dk --opensk --panic-console

Debugging memory allocations

You may want to track memory allocations to understand the heap usage of OpenSK. This can be useful if you plan to port it to a board with fewer available RAM for example. To do so, you can enable the --debug-allocations flag of the deploy.py script. This enables a custom (userspace) allocator that prints a message to the console for each allocation and deallocation operation.

The additional output looks like the following.

# Allocation of 256 byte(s), aligned on 1 byte(s). The allocated address is
# 0x2002401c. After this operation, 2 pointers have been allocated, totalling
# 384 bytes (the total heap usage may be larger, due to alignment and
# fragmentation of allocations within the heap).
alloc[256, 1] = 0x2002401c (2 ptrs, 384 bytes)
# Deallocation of 64 byte(s), aligned on 1 byte(s), from address 0x2002410c.
# After this operation, 1 pointers are allocated, totalling 512 bytes.
dealloc[64, 1] = 0x2002410c (1 ptrs, 512 bytes)

A tool is provided to analyze such reports, in tools/heapviz. This tool parses the console output, identifies the lines corresponding to (de)allocation operations, and first computes some statistics:

• Address range used by the heap over this run of the program,
• Peak heap usage (how many useful bytes are allocated),
• Peak heap consumption (how many bytes are used by the heap, including unavailable bytes between allocated blocks, due to alignment constraints and memory fragmentation),
• Fragmentation overhead (difference between heap consumption and usage).

Then, the heapviz tool displays an animated "movie" of the allocated bytes in heap memory. Each frame in this "movie" shows bytes that are currently allocated, that were allocated but are now freed, and that have never been allocated. A new frame is generated for each (de)allocation operation. This tool uses the ncurses library, that you may have to install beforehand.

You can control the tool with the following parameters:

• --logfile (required) to provide the file which contains the console output to parse,
• --fps (optional) to customize the number of frames per second in the movie animation.

cargo run --manifest-path tools/heapviz/Cargo.toml -- --logfile console.log --fps 50

Contributing

See Contributing.md.