Zymkey4 Quickstart

ZYMKEY4 is the fourth generation of the Zymbit security module designed specifically to work with Raspberry Pi and NVIDIA Jetson. It connects to the GPIO header of the SBC and uses the I2C bus and GPIO4 to communicate with the SBC CPU via an encrypted channel.

In this Getting Started guide we describe how to install your ZYMKEY4 to a Raspberry Pi running Raspbian or Ubuntu. The installation process is the same for both of these Linux distributions.

The Zymkey occupies 10 pins on the GPIO header. It can also be used with other GPIO devices attached, or other I2C devices attached. The correct address range and use of IO pins will be described in this guide as well.

Zymkey4 Hardware

A labeled diagram of the Zymkey4 hardware

The top and bottom of the Zymkey4 hardware showing the location of the GPIO header and other connectors.

Zymkey4 Pinout

A labeled diagram of the Zymkey4 pinout

The pinout of the header of the Zymkey4. Zymkey requires exclusive access to GPIO4, which can be remapped to another GPIO pin. It also share the {{< term/i2c >}} bus with the default address of 0x30.

Summary of Setup Steps

Installing the hardware
Install the battery on the Zymkey4, and connect it to the host single-board computer (SBC).
Establish an I2C connection
Enable the I2C bus on the host device in order to be able to communicate with the Zymkey.
Install the client software
These utilities provided by Zymbit are necessary to interact with the hardware module.
Test the installation
Your Zymkey is now temporarily bound to your SBC and ready for use in developer mode.

Installing the hardware

Battery Installation

Battery installation is not required for the Zymkey4 to function, but it is highly recommended if your device is vulnerable to physical access!

To maintain the real-time clock (RTC) and tamper detection features in the event of power loss, install a high quality 3V CR1025 coincell battery in the Zymkey4’s battery slot with +ve facing upward.

Battery Install

Hardware Installation


Installing your hardware correctly is important to avoid destroying your SBC or Zymkey. Be sure to follow the instructions below carefully. In particular:

  • Pay close attention to the images below to ensure the SBC’s GPIO pins are properly aligned with the ZYMKEY4’s header.
  • Ensure that your Raspberry Pi is powered down before proceeding.
  • Ensure that the coincell battery (if installed) is installed with the positive side (marked with +) facing upward.

Before installing

Power off your Raspberry Pi and disconnecting it from power entirely to ensure that neither the SBC or the ZYMKEY4 are damaged.

Attach hardware

Hold the ZYMKEY4 with the LED and battery holder facing upward. Then, carefully align the Zymkey’s connector with the first 10 GPIO pins of the Raspberry Pi.

Alignment of the Zymkey on the Raspberry Pi GPIO header

Press down firmly on the Zymkey to connect it to the GPIO pins of the Raspberry Pi. The Zymkey should fit relatively snug and maintain a tight interference fit around the pins.

Alignment of the Zymkey on the Raspberry Pi GPIO header (side view)

The Zymkey occupies 10 pins on the GPIO header. If the header of the Zymkey isn’t properly aligned with the GPIO header of the Raspberry Pi, both devices could be damaged.

Power on and confirm operation

After you have connected the hardware and are sure that the pins are properly aligned, power up your Raspberry Pi. You should see a blue LED blinking rapidly and consistently (5 blinks per second). This confirms that your Zymkey is operation but unconfigured.

Zymkey LED 5 per sec

If the blue LED blinks erractically, or not at all, then there is an installation error and you should check the connections.

Establish an I2C connection

For Raspian-based operating systems, you must configure the state of the I2C.

  1. Log in to your Raspberry Pi and run sudo raspi-config.
  2. Navigate to Interfacing Options -> I2C -> Would you like the ARM I2C interface to be enabled?
  3. Select yes, and confirm this choice.

Your I2C bus is now configured and ready to talk to the Zymkey. The default I2C address for the Zymkey is 0x30.


The default mode for the cpu scaling governor is ondemand. There have been some issues with the interaction between the zymkey and the I2C bus, when the governor is set to ondemand. We highly recommend to switching the governor to performance to get the most out of the zymkey.

Install the client software

Login to your host device and follow these steps to install the Zymkey’s client software.

The Zymkey will require a number of packages to be installed from the Raspbian and Zymbit apt repositories. The following setup script will be install a number of files and software packages on your system, including:

  • Zymbit .service files located in the /etc/systemd/system directory
  • pip

Ensure that curl is installed on your host:

sudo apt install curl

Download and install the necessary Zymbit services onto your device.

curl -G https://s3.amazonaws.com/zk-sw-repo/install_zk_sw.sh | sudo bash


Raspberry PI OS - Bullseye We are working on pushing a repository to directly support the Raspberry PI OS Bullseye release (10/30/2021). In the meantime, the Zymbit Buster repo will work. Substitute the following curl command for our standard installation script to use the Zymbit Buster repo:

curl -G http://s3.amazonaws.com/zk-sw-repo/install_zk_sw_bullseye.sh | sudo bash

Test the installation

When the software installation has completed, reboot your device. After the reboot has completed, the Raspberry Pi will perform an operation that will temporarily bind the Zymkey to your SBC. Once the Zymkey is bound to the SBC, the Zymkey’s blue LED should blink slowly–once every 3 seconds–to indicate that the binding is complete.

The quickest way to get started is to see the Zymkey’s various features at work by running these test scripts that were installed with the client software:

  • python3 /usr/local/share/zymkey/examples/zk_app_utils_test.py
  • python3 /usr/local/share/zymkey/examples/zk_crypto_test.py

Now you’re ready to start developing with Zymkey4 and Raspberry Pi. When it’s time to deploy your project, read our guide on enabling Production Mode: