How to set up Krux
Krux turns an off-the-shelf camera board into an air-gapped signing device, and most of the setup is getting the firmware onto it safely.
Buy a supported Kendryte K210 device such as the M5StickV, the Maix Cube, or a touchscreen board like the Yahboom or WonderMV. Flash the current firmware, v26.09.0, with Krux-Installer or by hand after checking its hash and signature. Create a seed phrase from dice rolls, back it up on paper or metal, and test that it restores. Then export the xpub to Sparrow as a QR code and sign by QR code or SD card.
What Krux is
Krux is open-source firmware for off-the-shelf Kendryte K210 devices that turns them into Bitcoin transaction signers. It talks to your wallet app through QR codes, SD cards, and thermal printers, and after the first install the device never needs to plug into your computer. The source is MIT or Apache 2.0 licensed.
The project calls itself a research and development project and tells you to use it at your own risk. I have not used Krux day to day. This guide is built from its documentation, source code, release notes, and incident record.
Step 1: pick a device
Every Krux device runs on the K210 chip. Most come assembled, so you flash the firmware and you are done. The Krux parts page compares them all, with these price ranges:
| Device | Price range | Screen | Worth knowing |
|---|---|---|---|
| M5StickV | $50 to $55 | 1.14 inch, buttons | Smallest, with a built-in battery |
| Maix Cube | $34 to $49 | 1.3 inch, 3-way button | Built-in battery |
| Yahboom K210 module | $45 to $61 | 2 inch touchscreen | Micro USB, ships with a 32 GB card |
| WonderMV | $58 to $86 | 2 inch touchscreen | Some SD cards make it restart |
| TZT | $48 | 2 inch touchscreen | Milled aluminum housing |
| Embed Fire | $74 | 2.4 inch touchscreen | Screen can shift slightly in the case |
| Maix Dock | $27 to $35 | 2.4 inch | Needs a rotary encoder, soldering, and a 3D-printed case |
The Maix Amigo, which had the biggest screen, is discontinued, though Krux still supports it. The chip itself is gone too: the v26.09.0 release notes say Krux runs on discontinued K210 hardware and needs contributors to port it to new boards. If you settle on one model, a spare board is cheap insurance. My Krux review weighs that risk.
Step 2: install the firmware and verify it
The current release is v26.09.0, from October 3, 2026. The first install goes over USB, and you have two sensible ways to do it:
- Use Krux-Installer, a desktop app for Windows, macOS, and Linux, currently at v0.0.24. Verify the installer first: the docs walk you through checking the GPG signature on its SHA-256 file, then the file's hash. Since v0.0.23 the installer ships with every firmware already downloaded and checked for hash and signature, so it fetches nothing while you flash.
- Flash by hand from the GitHub release. Check that the zip's SHA-256 hash matches the published one and that its signature verifies against the selfcustody public key in the Krux repository, then flash with the included ktool. The same page gives the command for each device.
After that first install, update by SD card. Copy the new firmware and its signature file to the card, and the device verifies the signature before it offers to install. Only official releases are signed, so later updates stay air-gapped and get checked by firmware you already trust.
Krux also has an experimental tamper check that turns a hash of the device's flash memory into an image and two pairs of words you learn to recognize. The docs note it only works if the firmware running it is legitimate, so set it up right after a verified install.
Step 3: create a seed phrase from dice
Choose New Mnemonic and pick a source: the camera, words you draw yourself, six-sided dice, or twenty-sided dice. The docs recommend dice, because generating true entropy is hard for an embedded device. A six-sided die needs at least 50 rolls for 12 words and 99 for 24, and a twenty-sided die needs 30 or 60. The camera option is labeled experimental, so skip it for a wallet that will hold savings.
Krux shows the SHA-256 hash of your rolls so you can check its math, and the docs say SeedSigner and the Bitcoiner Guide website use the same method, so the same rolls give the same words. Run that comparison with a test seed only, never the one you will fund.
Step 4: back up the seed phrase and test it
Write the words down in order, away from cameras, then move them to metal (see how to back up a seed phrase). Krux can also export the phrase as a SeedQR or Compact SeedQR for fast loading, and it can save an encrypted copy to the device or an SD card. Its own docs say encrypted storage is meant for convenience only and is not a long-term backup, because flash storage can degrade.
Test the backup before you fund it. The docs put this step first: create the seed phrase, back it up, and test the recovery before you set up a wallet app. Power off, load the wallet from your written words, and check that the fingerprint matches the one you saw when you created it.
Step 5: connect a wallet app
Krux works with Sparrow, Specter Desktop, Liana, Bitcoin Safe, Nunchuk, BlueWallet, Bitcoin Keeper, and BULL Wallet, and the docs warn it is incompatible with Electrum. With Sparrow:
- 1Load your seed on Krux and open Extended Public Key.
- 2Show the xpub as a QR code, or save it to an SD card as text.
- 3In Sparrow, create a wallet, add Krux as an air-gapped hardware wallet, and scan the QR. The Krux docs say to pick SeedSigner or Other if your app does not list Krux, and Sparrow's QR guide shows the screens.
- 4Confirm that the policy type, script type, fingerprint, and derivation in Sparrow match what Krux shows.
For multisig, the docs also have you load and back up the wallet descriptor on Krux. My Sparrow setup guide covers verifying Sparrow and connecting your own node.
Step 6: verify an address and sign
Krux can list your receive and change addresses, or scan one from your wallet app, to confirm it belongs to your seed. Send a small test amount, as the docs advise, then spend from it:
- 1Create the transaction in Sparrow and show it as a QR code, or save it to an SD card.
- 2On Krux, open Sign, then PSBT, and load it from the camera or the SD card.
- 3Check the recipient, amount, and fee on Krux's screen.
- 4Sign to a QR code or back to the SD card, then load the signed transaction into Sparrow and broadcast it.
Once that round trip works, move the rest with my guide to moving bitcoin to a hardware wallet.
Project status and security record
Krux changed hands in 2026. In the v26.08.0 notes, the previous maintainer wrote that K210 chips are no longer produced and that Krux would be archived unless another contributor took over. Jean Do accepted the role and shipped v26.09.0 in October.
That release fixed a 12-byte buffer overflow in the encryption code, which the maintainer judged not practically exploitable, with no action needed for existing encrypted backups. The release before it tightened the fee checks on PSBT screens and fixed a camera entropy overflow that only the discontinued Maix Bit could trigger. Every Krux entry is on my security incident tracker.
Next steps
Compare Krux with its closest rival in Krux vs SeedSigner and my SeedSigner setup guide, or see all three DIY options in best DIY signing devices. My Krux review has the rating and the trade-offs.
Frequently asked questions
Which devices does Krux support?
Krux runs on Kendryte K210 devices: the M5StickV, Maix Cube, Yahboom K210 module, WonderMV, TZT, Embed Fire, Maix Dock, and the discontinued Maix Amigo. The parts page lists prices and the quirks of each.
How do I update Krux firmware?
After the first USB install, copy the new firmware file and its signature to a microSD card and reboot the device. Krux checks the signature before it offers to install, so the device stays air-gapped.
Does Krux work with Electrum?
No. The Krux docs list Electrum as incompatible. Use Sparrow, Specter Desktop, Liana, or one of the phone wallets the docs name.
Does Krux store my seed phrase?
Only if you choose to save an encrypted copy on the device or an SD card. The docs call that a convenience, not a backup, so keep a written or metal copy and test it.
Is Krux safe for beginners?
It suits people comfortable flashing and verifying firmware. The project calls itself research and development software, its hardware is out of production, and it changed maintainers in 2026. A beginner is better served by one of my top hardware wallet picks.