Signet High-capacity

by Nth Dimension

An all-in-one encrypted USB flash drive, two-factor authentication token, and password manager

View all updates Sep 30, 2019

Alternate Device Uses

The Signet firmware has now been ported to Signet HC. Our next goal is to add two-factor authentication support. With the encouragement of Solo Keys we have started to integrate core portions of their FIDO2 implementation for the Somu device. Since their implementation is already certified by the FIDO alliance it should be easier to get Signet HC certified as well.

The video below demonstrates our successful porting of the Signet firmware to Signet HC, including how to initialize the device, create an account, and use the browser plugin to login to a website.

Signet HC client and browser plugin demo

Alternate uses for Signet HC

We designed the Signet HC hardware to be a suitable authentication tool and secure storage device. We also took a number of steps to make sure that our users could use it for other applications as well.

  • The case can be assembled and disassembled without damaging it using only flat head screwdriver
  • A power (3.3 V), ground, and three general purpose I/O pins (GPIO) have been routed to a pin header on the side of the circuit board
  • The microcontroller's single wire debug port has been routed to two large solder wire pads for real-time debugging

Here are a few ideas we’ve had about alternate uses:

A "Bad USB" testing platform

The term "Bad USB" refers to an exploit where a USB device can crash or compromise a system by purposefully violating the operating system’s expectations about how USB devices should behave. Signet HC could be used to run through a set of "Bad USB" experiments. It could use the button to cycle through tests and make a record of the results in the eMMC.

A computer case add-on

Desktop computer cases typically have a series of lights and buttons to show hard-disk activity or allow you to hard reset your computer. Signet HC could act as a second button for a configurable system action, and the button light could be used as a visual activity monitor, such as network activity, processor usage, case temperature, etc. The application could alter the brightness or blink rate to indicate measurement levels.

Hardware watchdog

Signet HC could act as a hardware watchdog: a hardware watchdog receives regular system signals, and will reset the system if it doesn’t receive a signal within a preset time frame (suggesting that the OS kernel has crashed). Hardware watchdogs are frequently used for systems that must run continuously (such as a server).

You could program a simple service on your system to send a periodic message to Signet HC, and wire the motherboard’s reset line to one of the Signet’s GPIO lines to allow it to reset the system if the service stops sending messages.

A secure One-time pad

A One-time pad is a kind of cryptographic key where there are as many bits in the key as there are bits to be encrypted. Since Signet HC microcontroller contains a high-speed true random number generator it could quickly fill up the eMMC with a large one-time pad. The one-time pad could then be shared with a second device over an encrypted channel and the devices could be used together to send highly secure messages between two people.

Signet HC with wireless features

To make Signet HC the size we wanted, we couldn’t find enough room for a Bluetooth or WIFI chip. However, since two of Signet HC’s GPIO lines can be configured as a UART port, you can potentially connect it to a wireless enabled board (such as the Tiny Pico) and communicate with it over the UART port. This would allow Signet HC to be used or monitored at a distance, even opening up the possibility of web applications.

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Product Choices


Signet HC

An all-in-one physically secured USB flash drive, authentication tool, and personal information manager you can take with you wherever you go.


USB Extension Cable

Helps keep your Signet HC close to your keyboard when the closest USB port is too far away. Can also reduce strain on the device's connector to increase its lifespan. 3'

USB Extension Cable


Micro-USB Host Adapter Cable

Connects your Signet HC to a USB-micro Android device. 6"


Nth Dimension

Producer of privacy and security focused open source electronics.

Neils Nesse


Mingjane Wu

Technical writer / UX designer


PCBA Manufacturer

Sea Sky Tooling

injection molding

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