Pico FIDO

This project transforms your Raspberry Pi Pico into an integrated FIDO Passkey, functioning like a standard USB Passkey for authentication.

Features

Pico FIDO includes the following features:

CTAP 2.1 / CTAP 1
WebAuthn
U2F
HMAC-Secret extension
CredProtect extension
User presence enforcement through physical button
User verification with PIN
Discoverable credentials (resident keys)
Credential management
ECDSA authentication
Support for SECP256R1, SECP384R1, SECP521R1, and SECP256K1 curves
App registration and login
Device selection
Support for vendor configuration
Backup with 24 words
Secure lock to protect the device from flash dumps
Permissions support (MC, GA, CM, ACFG, LBW)
Authenticator configuration
minPinLength extension
Self attestation
Enterprise attestation
credBlobs extension
largeBlobKey extension
Large blobs support (2048 bytes max)
OATH (based on YKOATH protocol specification)
TOTP / HOTP
Yubikey OTP
Challenge-response generation
Emulated keyboard interface
Button press generates an OTP that is directly typed
Yubico YKMAN compatible
Nitrokey nitropy and nitroapp compatible

All features comply with the specifications. If you encounter unexpected behavior or deviations from the specifications, please open an issue.

Security Considerations

Pico FIDO is an open platform, so exercise caution. The flash memory contents can be easily dumped, potentially revealing private/master keys. It is not feasible to encrypt the content, meaning at least one key (the master key) must be stored in clear text.

If the Pico is stolen, the private and secret keys can be accessed.

Download

Please visit the Release page to download the UF2 file for your board.

Note that UF2 files are shipped with a dummy VID/PID to avoid license issues (FEFF:FCFD). If you plan to use it with OpenSC or similar software, you will need to modify the Info.plist of the CCID driver to add these VID/PID values or use the Pico Patcher tool.

Alternatively, you can use the legacy VID/PID patcher with the following command:

./patch_vidpid.sh VID:PID input_hsm_file.uf2 output_hsm_file.uf2

You can use any VID/PID (e.g., 234b:0000 from FISJ), but remember that you are not authorized to distribute the binary with a VID/PID that you do not own.

For ease of use, the pure-browser option Pico Patcher tool is highly recommended.

Build

Before building, ensure you have installed the toolchain for the Pico and that the Pico SDK is properly located on your drive.

git clone https://github.com/polhenarejos/pico-fido
cd pico-fido
mkdir build
cd build
PICO_SDK_PATH=/path/to/pico-sdk cmake .. -DPICO_BOARD=board_type -DUSB_VID=0x1234 -DUSB_PID=0x5678
make

Note that PICO_BOARD, USB_VID, and USB_PID are optional. If not provided, the default Pico board and VID/PID FEFF:FCFD will be used.

After make finishes, the binary file pico_fido.uf2 will be generated. Put your Pico board into loading mode by holding the BOOTSEL button while plugging it in, then copy the UF2 file to the new USB mass storage Pico device. Once copied, the Pico mass storage will disconnect automatically, and the Pico board will reset with the new firmware. A blinking LED will indicate that the device is ready to work.

Remark: Pico FIDO uses the HID interface, so VID/PID values are irrelevant in terms of operativity. You can safely use any arbitrary values or the default ones. They are only necessary in case you need to use 3rd-party tools from other vendors.

Led blink

Pico FIDO uses the led to indicate the current status. Four states are available:

Press to confirm

The Led is almost on all the time. It goes off for 100 miliseconds every second.

Idle mode

In idle mode, the Pico FIDO goes to sleep. It waits for a command and it is awaken by the driver. The Led is almost off all the time. It goes on for 500 milliseconds every second.

Active mode

In active mode, the Pico FIDO is awaken and ready to receive a command. It blinks four times in a second.

Processing

While processing, the Pico FIDO is busy and cannot receive additional commands until the current is processed. In this state, the Led blinks 20 times in a second.

Driver

Pico FIDO uses the HID driver, which is present in all operating systems. It should be detected by all OS and browser/applications just like normal USB FIDO keys.

Tests

Tests can be found in the tests folder. They are based on FIDO2 tests from Solokeys but adapted to the python-fido2 v1.0 package, which is a major refactor from the previous 0.8 version and includes the latest improvements from CTAP 2.1.

To run all tests, use:

pytest

To run a subset of tests, use the -k <test> flag:

pytest -k test_credprotect

Credits

Pico FIDO uses the following libraries or portion of code:

MbedTLS for cryptographic operations.
TinyUSB for low level USB procedures.
TinyCBOR for CBOR parsing and formatting.