DIY FIDO2 Security Key with STM32L4

The Inspiration

Security is often a "black box" for most users. Commercial FIDO2 keys are great, but as an electronics engineer, I wanted to understand—and build—the hardware that protects our digital lives. I decided to create DongleSDK, a fully open-source FIDO2 security key that gives the power back to the user.

How It Works

The heart of the project is the STM32L432KC microcontroller. I chose this chip for its excellent power efficiency and robust security features. The system operates on a challenge-response mechanism:

Hardware: A compact USB form factor designed for portability.

• Hardware: A compact USB form factor designed for portability.

Encryption: I implemented AES-256 to ensure that the communication between the key and the host is virtually unhackable.

• Encryption: I implemented AES-256 to ensure that the communication between the key and the host is virtually unhackable.

SDK & Integration: To make the hardware useful, I developed a custom C# SDK (DongleSDK). This allows any Windows-based application to interact with the key seamlessly via a dedicated Windows Forms interface.

• SDK & Integration: To make the hardware useful, I developed a custom C# SDK (DongleSDK). This allows any Windows-based application to interact with the key seamlessly via a dedicated Windows Forms interface.

The Build Process

Building this wasn't just about the code. I used FreeCAD to design a custom, 3D-printable enclosure that protects the electronics while keeping a slim profile.

Firmware: Developed in C/C++ specifically for the STM32 architecture.

• Firmware: Developed in C/C++ specifically for the STM32 architecture.

Hardware: Prototyped on a breadboard before moving to a custom PCB layout.

• Hardware: Prototyped on a breadboard before moving to a custom PCB layout.

Enclosure: Multiple iterations in FreeCAD to get the perfect fit for the USB connector.

• Enclosure: Multiple iterations in FreeCAD to get the perfect fit for the USB connector.

Why Open Source?

The goal of this project is to provide a blueprint for others to build their own security hardware. Whether you are a student learning about cryptography or a developer looking for a secure authentication layer, this project provides the tools you need.