Krux

• Name: Krux
• URL: https://selfcustody.github.io/krux/
• Category: bitcoin signing-firmware infrastructure / DIY self-custody signer platform / airgapped QR-and-SD workflow / mnemonic-backup tooling
• Tags: bitcoin-ecosystem
• Summary: Krux is an open-source Bitcoin signing-firmware project that turns off-the-shelf Kendryte K210 devices into airgapped signing tools. Its primary-source surface emphasizes cheap commodity hardware, offline PSBT signing over QR codes and SD cards, compatibility with multiple coordinator wallets, optional thermal-printer and backup tooling, a simulator for trying the UX without hardware, and a clear no-formal-audit warning. That makes Krux better cataloged as DIY signer firmware and self-custody infrastructure rather than as a single branded hardware wallet.
• What it does:
  • Provides open-source firmware that converts supported K210 devices such as Maix Amigo, M5StickV, Yahboom, TZT, WonderMV, and others into Bitcoin signing devices
  • Keeps signing operations offline using PSBT workflows over QR codes or SD cards instead of USB-connected wallet operation
  • Supports single-signature, multisignature, and descriptor-oriented Bitcoin wallet flows with third-party coordinator wallets
  • Includes tooling for mnemonic creation, recovery, encryption, mnemonic-backup workflows, and optional offline printing / engraving helpers
  • Publishes a simulator and installer path so users and contributors can test Krux before sourcing hardware or building firmware from source
  • Maintains public device / parts documentation that compares compatible boards by screen, camera, battery, price, and assembly requirements
• Key claims:
  • The official docs frame Krux as open-source Bitcoin signing firmware rather than a finished consumer hardware product, which is the most important categorization signal
  • The getting-started docs explicitly say signing is done offline via QR code or SD card using PSBT and that Krux never handles transaction broadcasting itself
  • The same getting-started page is valuable because it names compatible coordinator wallets including Sparrow, Specter Desktop, Liana, Bitcoin Safe, Nunchuk, BlueWallet, Bitcoin Keeper, and BULL Wallet, while also noting Electrum incompatibility
  • The docs and README jointly show Krux spanning more than transaction signing: it also supports mnemonic backup creation/recovery, encryption options, optional thermal-printer workflows, and multiple device form factors
  • The parts list is especially useful because it makes the project’s hardware philosophy explicit: commodity K210 boards in different shapes and prices are the substrate, with some models requiring DIY assembly or accessories
  • The README’s simulator, installer, and developer-tooling sections show Krux operates as an auditable firmware platform with a real contributor surface, not just a static firmware drop
  • The README prominently warns that the software has not been formally audited by a third party, which is an important operational caveat to preserve in the catalog
• Whitepaper: No canonical Krux whitepaper or litepaper surfaced in this pass. The clearest current sources of truth are the official docs site, getting-started and parts pages, and the public GitHub repository / README; see ../whitepapers/krux-primary-sources-2026-05-01.md.
• Sources:
  • https://selfcustody.github.io/krux/
  • https://selfcustody.github.io/krux/getting-started/
  • https://selfcustody.github.io/krux/parts/
  • https://github.com/selfcustody/krux
  • https://github.com/selfcustody/krux/blob/main/README.md

Internal linkages

• Strongest comparison points: seedsigner, foundation-devices, and sparrow-wallet.

• Reusable lens: Krux is worth keeping when the comparison is about cheap commodity-hardware signers, QR or SD transport, and coordinator-wallet dependence rather than brand polish.

• Last reviewed: 2026-05-31 UTC