Knox Key Kicad

Knox Key

This is a custom USB-C FIDO2 security key. The repository contains the KiCad 9 hardware files (schematics, PCB layout, fab outputs) and the authenticator firmware.

The hardware pairs an STM32L433 microcontroller with an ATECC608B secure element. The project started out as an STM32F072 design (originally named "kryptonite") but was later reworked to use the L433.

Hardware Details

• MCU: STM32L433CB (LQFP-48) with an 8 MHz crystal and internal USB PHY.
• Crypto: ATECC608B secure element on I2C (PB6/PB7) for hardware TRNG.
• Port: USB Type-C running USB 2.0 full speed.
• Feedback: Single RGB LED. Green is success, red is error, blue/yellow indicates waiting for user presence.
• Button: Tactile button for user presence verification (supports single, double, and long presses).
• Power: USB bus-powered via a 3.3V MCP1700 LDO.
• PCB: 2-layer layout.

Working with KiCad

Open Knox Key Kicad.kicad_pro in KiCad 9. Make sure to run ERC and DRC before exporting manufacturing outputs. If you are hand-assembling the board, open bom/ibom.html in a web browser for the interactive BOM.

Firmware

The firmware is in firmware/knoxkey/ and implements a FIDO2 / CTAP2 authenticator. Random numbers are pulled from the ATECC608B over I2C, while credential wrapping uses software AES. User presence is verified via the hardware button.

To build the target for the STM32L433:

cd firmware/knoxkey
cmake -B build/stm32l433-release -S . --preset default -DBUILD_TARGET=stm32l433
cmake --build build/stm32l433-release -j 8

Binaries (.elf, .hex, .bin) will compile into build/stm32l433-release/targets/stm32l433/. Flash them using an ST-Link or via USB DFU mode.

Bill of Materials

17 line items, 29 components total. Machine-readable versions: BOM.csv and BOM.md. manufacturing/bom.csv has the same data in the exact format JLCPCB's assembly service expects.

* R6/R7/R8 are still labeled with placeholder values (R/G/B) in the schematic rather than an actual resistance — confirm before ordering a board that needs them populated.

Manufacturing & Ordering

All files needed to manufacture the board are inside manufacturing/:

• gerbers/ and knox-key-gerbers.zip — Bare-board fabrication files.
• bom.csv — Bill of Materials (with LCSC part numbers).
• positions.csv — Pick-and-place component coordinates (CPL).
• designators.csv — Reference designator mappings.
• netlist.ipc — IPC-D-356 netlist.

For JLCPCB: Upload knox-key-gerbers.zip for the PCB, and use bom.csv and positions.csv for SMT assembly. Add a solder paste stencil to your order if you plan to solder manually. Don't forget to regenerate these from KiCad if you modify the layout!

Renders

Security Warning

This is a hobbyist project and has not undergone any formal security audit. The ATECC608B chips ship unprovisioned, meaning you must load your own keys onto the secure element. Do not use this for production environments without reviewing the firmware and provisioning process yourself.

License

GPLv3. See LICENSE for details.