TurtleAuth Is a DIY GPG USB Key Based on the STM32
Updated version with quality-of-life improvements, including a PCB sandwich design.
Why buy a GPG key device when you can build one? Samuel, The Static Turtle, created TurtleAuth — a DIY GPG USB key. With this open design, you can make your own that uses open source firmware to store keys and appear to the host as a smartcard.
TurtleAuth is a USB flash drive-sized device. On one side is a USB-A connector and on the other is a loop for placement on a keychain. The top has two LEDs and a capacitive touch button.
Pictured above is the latest version. The previous version suffered a slight mistake with the placement of the USB port. As a result, its location was less optimal for attaching to some host computers. Version 2.1 of TurtleAuth solves this issue.
Additionally, the new version features a three PCB sandwich design. The bottom circuit board contains the USB port, STM32 microprocessor, and related components on a single side. A top circuit board has cutouts for the LEDs and the capacitive touch button. Finally, a center PCB acts as a spacer for the two.
When soldered together, the TurtleAuth PCB sandwich is complete. Hopefully, this new sandwich design better protects the small components- an essential feature if attached to a keychain! While the hardware received an update, the software remained unchanged.
Like the previous version, TurtleAuth 2.1 runs Gnuk. Gnuk is a firmware for the STM32 that turns it into a USB cryptographic token for GNU Privacy Guard. This implementation supports OpenPGP card protocol version 3. Samuel's Hackster project page documents the overall steps needed for you to get the firmware onto a TurtleAuth.
You can obtain the EasyEDA design files from this GitHub repository to build one. As a little warning, the PCB uses components 0402 passive components. However, as Samuel found, some of the footprints will accommodate 0603s! Once built, check out Samuel's Gnuk repo for the necessary firmware.
