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solokeys/solo1

Free

Solo 1 firmware in C

FreeFree tier
Type
Open Source
Company
SoloKeys
Visit Website GitHub (38 stars)

About solokeys/solo1

Solo 1 firmware is the open-source implementation for SoloKeys' first-generation security key. It supports FIDO2 and U2F authentication standards (CTAP2 and CTAP) over USB and NFC, providing strong two-factor authentication and password-less login. The firmware is written in C, runs on the STM32L432 microcontroller, and is designed to be easily ported to other hardware. For development, it can run as a standalone application on Windows, Linux, and macOS without any hardware. It includes hardware-backed security features such as true random number generation, secure isolation, and flash protection. A special 'Solo for Hacker' variant allows users to customize the firmware, including changing LED colors and building advanced applications.

Key Features

FIDO2 and U2F (CTAP2/CTAP) support
USB and NFC communication
Runs on STM32L432 microcontroller, easily portable to other MCUs
Standalone desktop application for Windows, Linux, and macOS
Hardware security: true random number generation, secure isolation, flash protection
256 KB memory for hardened crypto and future features
Open source with no NDA required for development
Solo for Hacker variant allows firmware customization (LED colors, advanced apps)

Pros & Cons

Pros
  • Fully open source with permissive licensing (MIT/Apache 2.0)
  • No hardware required for development – runs as a desktop app
  • Supports both FIDO2 and legacy U2F protocols
  • Hardware-backed security features (TRNG, isolation, flash protection)
  • Active community and multilingual guides
  • Customizable Hacker version for advanced users
Cons
  • Solo for Hacker variant is not secure for production use – physical access can compromise it
  • Firmware is specific to Solo v1 hardware; Solo v2 is a separate product
  • Requires embedded development knowledge for porting or customization
  • Limited memory (256 KB) may constrain complex additional features

Best For

Strong two-factor authentication for online accountsPassword-less login via FIDO2Protection against phishing and other online attacksDeveloping and testing custom firmware on Solo for Hacker devicesLearning embedded security and hardware authentication

FAQ

What is Solo?
Solo is an open source security key that supports FIDO2 and U2F standards for strong two-factor authentication and password-less login.
What protocols does Solo firmware support?
It supports FIDO2 (CTAP2) and U2F (CTAP) over USB and NFC.
Can I run Solo firmware without a physical security key?
Yes, the firmware can run as a standalone application on Windows, Linux, and macOS for development and testing.
What hardware is the firmware built for?
The main implementation targets the STM32L432 microcontroller, but it is designed to be easily portable to other hardware.
Is Solo Hacker secure for everyday use?
No, the Solo for Hacker variant is unlocked for customization and is not considered secure – it should only be used for development.