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Build Your Own FIDO2 Security Key with nRF52840 and OpenSK

An open-source USB FIDO2 security key built around the Nordic nRF52840 and Google's OpenSK firmware.

This project demonstrates how to build a hardware-backed authentication device that can be used with websites and services supporting FIDO2 / WebAuthn.

The custom hardware uses the nRF52840's native USB interface and hardware-assisted cryptography to implement the security-key functionality. The device communicates with the host computer over USB and keeps the credential's private key on the security key rather than transferring it to the computer or website.

Features

  • FIDO2 / WebAuthn authentication
  • nRF52840-based custom hardware
  • OpenSK open-source security-key firmware
  • USB HID FIDO2 transport
  • Hardware-assisted cryptography using the nRF52840
  • Credential private key remains on the security key
  • USB DFU / UF2 firmware updates
  • Custom capacitive touch input for user presence
  • RGB LED for status indication
  • Custom compact PCB
  • Open-source hardware and firmware modifications

How It Works

The security key acts as a FIDO2 authenticator between the browser and the website.

During registration, the security key generates a unique credential key pair:

                 Registration

Website
   │
   │ Registration request
   ▼
Browser
   │
   │ FIDO2 / CTAP2 over USB HID
   ▼
OpenSK on nRF52840
   │
   ├── Generate credential key pair
   │
   ├── Private key ──► Stored on security key
   │
   └── Public key ───► Website