Air-gapped Bitcoin signing
on the ESP32-P4
Kern turns an inexpensive touchscreen dev board into a powerful signing device. Bitcoin only, written in plain C: a maxCmalist signer.
Kern turns an inexpensive touchscreen dev board into a powerful signing device. Bitcoin only, written in plain C: a maxCmalist signer.
Five off-the-shelf boards. Each one needs a MIPI CSI camera module.
| Board | Target | Display | Camera |
|---|---|---|---|
| Waveshare ESP32-P4 4B | wave_4b | 720×720 MIPI DSI | Sold separately |
| Waveshare ESP32-P4 3.5″ | wave_35 | 320×480 SPI | OV5647, included |
| Waveshare ESP32-P4 5″ | wave_5 | 720×1280 MIPI DSI | OV5647, included |
| Waveshare ESP32-P4 4.3″ | wave_43 | 480×800 MIPI DSI | OV5647, included |
| CrowPanel Advanced 7″ / 10.1″ | crowpanel | 1024×600 MIPI DSI | SC2336, included |
Kern drives both the OV5647 and the SC2336 and probes for whichever one is attached at boot, so either sensor works on any of the boards. 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.
These boards carry an ESP32-C6 radio co-processor alongside the P4. Kern does not use it and holds it in reset mode. Users can remove or physically disable it if desired.
From an unflashed board to a working signer in a few minutes.
Any of the five boards above. All but the 4B come with a camera in the box; for the 4B, add an OV5647 module with autofocus.
The web flasher writes the latest build over USB using Web Serial, with no toolchain to install. Requires Chrome or Edge 89+.
Generate a mnemonic from dice rolls or the camera, or restore one you already have by typing it or scanning a QR code.
Full user documentation is not written yet. For now, these live in the repository.
Questions, testing reports and development chat.