Krux (DIY signer)

Overview

Krux is open-source firmware that turns inexpensive, off-the-shelf development boards (typically K210-based devices like the M5StickV or Maix Amigo) into a fully air-gapped Bitcoin signer. Like SeedSigner, it's a do-it-yourself, maximally verifiable approach for people who would rather build and audit their own signing device than buy a sealed commercial product. It communicates only via QR codes through the board's camera and screen.

The appeal is verifiability and cost. Because everything is open-source and you flash the firmware onto cheap hardware yourself, you can inspect exactly what your signer runs, and you can build multiple units cheaply — useful for multisig setups distributed across locations. Krux supports single-key and multisig wallets, works with software like Sparrow, and can operate in a way that avoids persisting your seed.

The honest trade-offs are real. It's DIY, so you source compatible hardware and flash it yourself, and there's no dedicated secure element — security rests on the air-gapped design, the open-source code, and your own operational discipline rather than tamper-resistant hardware. Entering your seed and driving a QR workflow takes more care and effort than a plug-and-play wallet, and the target user is clearly a technical tinkerer. For those who value a fully open, build-it-yourself, air-gapped signer — especially for multisig or as a verifiable second option — Krux is a respected choice; anyone wanting ease should buy a finished device instead.