Krux

Krux is open-source firmware that turns inexpensive Kendryte K210 boards into air-gapped Bitcoin signing devices. It supports single-signature and multisignature wallets, moves PSBTs over QR codes or SD cards, and includes tools for message signing, backups, and offline wallet review.

Because Krux runs on widely available hardware, users can flash supported devices themselves or build a signer from off-the-shelf parts. Public docs, broad coordinator compatibility, and the companion Krux Installer make the project accessible to people who want air-gapped signing without paying for a proprietary hardware wallet.

Recent public work has pushed Krux well beyond a basic signer. The project now supports more devices, clearer descriptor handling, stronger offline backup tooling, and regular security hardening across its QR, PSBT, and SD-card flows.

Why fund it?

Air-gapped self-custody should be open, inspectable, and affordable. Krux lowers the cost of secure signing and gives users a firmware stack they can audit, improve, and adapt to locally available hardware.

That matters even more in places where import fees can make commercial hardware wallets expensive. OpenSats first supported Krux in the third wave of Bitcoin grants and has continued backing the project as it expanded device support, coordinator compatibility, and signer safety.

What's next?

Recent public updates show Krux pushing on three fronts: broader hardware support, smoother signer UX, and tighter security. Releases through v26.04.0 added more supported devices, improved descriptor and QR handling, and shipped a broad set of safety checks around PSBT parsing, KEF decryption, and SD-card inputs.

The public roadmap is still moving toward faster QR tooling, continued Kapps work, and more polished device flows. The Open Hardware for Open Money report is a good snapshot of where the project has been heading across firmware releases, new device ports, and ongoing signer UX work.

If you want to dig deeper, start with the project site, the main repository, the grant announcement, or the release history.