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Kern is a young open-source project building an air-gapped Bitcoin signing device on the ESP32-P4. The chip has no radio, so keys are generated and used on hardware that physically cannot reach a network. Transactions cross the air gap as QR codes or over an SD card.

It signs PSBTs for single-sig, multisig and miniscript policies on both native segwit and taproot, built on libwally, the same core library used by Blockstream Jade.

Warning: Kern is under active development and has not been audited. Secure boot is not enabled by default and builds are unvetted development snapshots. Do not use Kern to manage real savings.

Hardware

Kern supports four Waveshare ESP32-P4 boards and one Elecrow CrowPanel board:

Board	Display	Touch	Camera
ESP32-P4-WiFi6-Touch-LCD-4B (wave_4b)	720x720 MIPI DSI	GT911	sold separately, OV5647 with autofocus recommended
ESP32-P4-WiFi6-Touch-LCD-3.5 (wave_35)	320x480 SPI	FT5x06	OV5647, included
ESP32-P4-WiFi6-Touch-LCD-5 (wave_5)	720x1280 MIPI DSI	GT911	OV5647, included
ESP32-P4-WiFi6-Touch-LCD-4.3 (wave_43)	480x800 MIPI DSI	GT911	OV5647, included
CrowPanel Advanced 10.1" ESP32-P4 and 7" siblings (crowpanel)	1024x600 MIPI DSI	GT911	SC2336, included

ESP32-P4 does not contain radio (WiFi, BLE), but these boards have a radio in a secondary chip (ESP32-C6 mini). Later the project will migrate to use radio-less, simpler and cheaper boards with ESP32-P4 only.

A MIPI CSI camera module is required for all boards. Kern ships drivers for the OV5647 and SC2336 sensors and probes for whichever one is attached at boot, so either sensor works on any board. The 4B is the one board sold without a camera: pair it with an OV5647 module carrying a DW9714 voice coil motor, which is the only combination that gets autofocus.

Prerequisites

Kern targets ESP-IDF v6.0.2. Install it for the esp32p4 target:

git clone --depth 1 --recurse-submodules --shallow-submodules -b v6.0.2 https://github.com/espressif/esp-idf.git ~/esp/esp-idf
~/esp/esp-idf/install.sh esp32p4
. ~/esp/esp-idf/export.sh

Build

Cloning the Repository

This project uses git submodules. You have two options:

Option 1: Clone with submodules (Recommended)

When cloning the project for the first time, make sure to clone it recursively to include all submodules:

git clone --recursive https://github.com/odudex/Kern.git

Option 2: Initialize submodules after cloning

If you've already cloned the repository without the --recursive flag, you can initialize and update the submodules with:

git submodule update --init --recursive

Building the Project

Build with just (recommended) or idf.py directly. All just commands accept a board parameter, one of wave_4b (default), wave_35, wave_5, wave_43, or crowpanel:

just build              # Build for wave_4b (default)
just build wave_35      # Build for wave_35
just build wave_5       # Build for wave_5
just build wave_43      # Build for wave_43
just build crowpanel    # Build for CrowPanel 7" / 10.1"
just flash wave_5       # Flash for wave_5
just monitor            # Serial monitor
just clean              # Wipe all build_<board> dirs + sdkconfig

Or using idf.py directly:

# wave_4b
idf.py -D 'SDKCONFIG_DEFAULTS=sdkconfig.defaults;sdkconfig.defaults.wave_4b' build

# wave_35
idf.py -D 'SDKCONFIG_DEFAULTS=sdkconfig.defaults;sdkconfig.defaults.wave_35' build

# wave_5
idf.py -D 'SDKCONFIG_DEFAULTS=sdkconfig.defaults;sdkconfig.defaults.wave_5' build

# wave_43
idf.py -D 'SDKCONFIG_DEFAULTS=sdkconfig.defaults;sdkconfig.defaults.wave_43' build

# crowpanel (7" / 10.1")
idf.py -D 'SDKCONFIG_DEFAULTS=sdkconfig.defaults;sdkconfig.defaults.crowpanel' build

Note: just builds each board into its own build_<board>/ directory, so switching boards needs no clean. The raw idf.py commands above share the default build/ directory and sdkconfig: run idf.py fullclean && rm sdkconfig when switching boards that way.

Note: The first build auto-generates dev_signing_key.pem (gitignored) and every build is signed with it. This is required to boot: the firmware refuses to run unsigned images. This key is a per-clone development key that carries no trust and never leaves your machine. Official releases are signed offline with the project's release key instead, so a self-built device only accepts SD-card updates built from the same clone; flash releases over USB.

Desktop Simulator

The simulator renders the full LVGL UI in an SDL2 window, matching each board's resolution:

just sim                # Run simulator as wave_4b (720x720) with webcam (V4L2)
just sim wave_35        # Run simulator as wave_35 (320x480)
just sim wave_5         # Run simulator as wave_5 (720x1280)
just sim wave_43        # Run simulator as wave_43 (480x800)
just sim crowpanel      # Run simulator as crowpanel (1024x600)
just sim-build wave_35  # Build only
just sim-clean          # Remove simulator build artifacts
just sim-reset          # Wipe simulator data (factory reset)
just sim-qr IMG         # Run with a QR image
just sim-no-cam         # Run without camera

Switching simulator boards also requires just sim-clean first. See simulator/README.md for details.

Full Clean

After updating ESP-IDF or switching branches with significant build changes, do a full clean to avoid stale artifacts:

idf.py fullclean
rm sdkconfig
idf.py set-target esp32p4
idf.py build

Build Options

Enable/disable Auto-focus

To enable camera auto-focus, enable camera focus motor on menuconfig:

CONFIG_CAM_MOTOR_DW9714=y
CONFIG_CAMERA_OV5647_ENABLE_MOTOR_BY_GPIO0=y

Web Flasher

The easiest way to flash Kern is the browser-based flasher, which requires no local toolchain. It works in Google Chrome or Microsoft Edge (version 89+) via the Web Serial API.

Live flasher: https://odudex.github.io/Kern/flash/

The flasher offers two modes:

• Latest CI Build: fetches firmware built by the most recent master push directly from the site and flashes it to the selected board.
• Custom ZIP Bundle: accepts a firmware-<board>.zip artifact downloaded from the Actions tab to flash any PR or older build.

Warning: CI builds are unvetted development snapshots from a young, unaudited project. Secure boot is not enabled; do not use flashed firmware to manage real savings.

Note: The project site and flasher are deployed automatically on every successful push to master, from site/ in this repository. To enable it for your fork, go to Settings → Pages and set the source to GitHub Actions. To preview the site locally, run just site and open http://localhost:8000. Web Serial works on localhost, so you can flash a real board from the local copy.

Flashing CI Build Artifacts

Every pull request and push to master produces a firmware artifact for each supported board via the Test All Builds workflow. These builds are useful for testing unreleased changes without setting up a local toolchain.

Requirements

• Python 3
• USB cable connected to the board

Steps

1. Open the Actions tab of the repository on GitHub and select the workflow run you want.

2. Scroll to the Artifacts section at the bottom of the run summary and download the zip for your board (e.g. firmware-wave_4b).

3. Unzip the package:

   unzip firmware-wave_4b.zip -d firmware-wave_4b
   cd firmware-wave_4b

   The zip contains, among other files:

   • bootloader.bin: bootloader
   • partition-table.bin: partition table
   • ota_data_initial.bin: OTA data partition
   • kern.bin: application firmware
   • flasher_args.json / flash_args: pre-computed flash offsets

4. Create a Python virtual environment and install esptool:

   python3 -m venv venv
   source venv/bin/activate
   pip install esptool

5. Flash using the pre-computed offsets from flash_args:

   esptool --chip esp32p4 --baud 460800 write_flash $(cat flash_args)

Flashing Pre-releases

Pre-release firmware is provided for testing purposes only. Do not use pre-release builds as a signer for real savings.

Supported Devices

Device	Board	Display
wave_4b	Waveshare ESP32-P4-WiFi6-Touch-LCD-4B	720x720 MIPI DSI
wave_35	Waveshare ESP32-P4-WiFi6-Touch-LCD-3.5	320x480 SPI
wave_5	Waveshare ESP32-P4-WiFi6-Touch-LCD-5	720x1280 MIPI DSI
wave_43	Waveshare ESP32-P4-WiFi6-Touch-LCD-4.3	480x800 MIPI DSI
crowpanel	CrowPanel Advanced 7" / 10.1" ESP32-P4	1024x600 MIPI DSI

Requirements

• Python 3
• USB cable connected to the board

Steps

1. Download the zip for your device from the Releases page (e.g. kern-wave_4b-v0.0.3.zip).

2. Unzip the package:

unzip kern-wave_4b-v0.0.3.zip

The zip contains:

• bootloader.bin: bootloader
• partition-table.bin: partition table
• firmware-signed.bin: application firmware (signed; also the file for SD-card updates)
• kern-v0.0.3.hex: single-file image (all of the above, Intel HEX)

3. Create a Python virtual environment and install esptool:

python3 -m venv venv
source venv/bin/activate
pip install esptool

4. Flash the single-file image:

esptool --chip esp32p4 --baud 460800 write-flash 0x0 kern-v0.0.3.hex

Note: The .hex image is sparse: it writes only the regions it contains, so the NVS partition (PIN, settings) and stored data survive reflashing. For a factory-clean install, erase everything first: esptool --chip esp32p4 erase-flash, then flash the image.

Updating via SD card

A device already running signed firmware updates without any computer: copy firmware-signed.bin from the zip onto a SD card, insert it, and go to Settings → Firmware Update. The device verifies the signature before installing and keeps the previous firmware as an automatic fallback.

Community

Development chat, testing reports and questions happen in the Telegram group: t.me/kern_custody.

Bug reports and pull requests are welcome on GitHub.

References

Kern is strongly inspired by Krux, sharing similar but simplified UI elements and flow.

Blockstream Jade was a strong inspiration for the decision to use C language for efficient use of the hardware. Additionally, Kern uses the same core library Jade does, libwally, is shared with Jade.

The simplicity and UI polish of SeedSigner and the security focus of the pioneering Specter-DIY were also strong inspirations.

Roadmap

Contributing

License

MIT