Air-gapped bitcoin signing · 4 models

Try the SeedSigner in your browser before you buy one

  1. Try
  2. Rehearse
  3. Verify
  4. Own

Anyone can sell you one of these. Air-gapped means it signs your bitcoin without ever touching the internet. I can hand you the device in a browser tab first, check the firmware you flash without a terminal, and give you a Bitcoin network to rehearse a multisig on. Then you pick a model.

Run one in your browser Compare the 4 models

The simulator is free. The device is from €135.00, VAT included.

bitsaga.be/seedsigner-simulator
The SeedSigner simulator running the wallet's home screen in a browser tab
This is a browser tab. The real firmware, running in your browser, with your keyboard as the buttons and your webcam as the QR scanner.

Try it, verify it, practise on it.
Before you pay.

These are the parts you can check yourself, right now, before you spend anything.

01 The device, in a browser tab

Try one before anyone asks you for money

The real SeedSigner firmware runs in your browser. Not a video, not a re-creation of the menus: the actual Python from the device, running in your browser, driven by the wallet's own controller. Walk the menu tree, load a seed, add a passphrase, export an xpub, sign a transaction, back a seed up as a SeedQR.

It is pinned to a published upstream release tag, and the build is reproducible, so you can rebuild the wallet yourself and check that the file this site served you is byte for byte the one the pin describes. Half an hour with it will tell you more than any review.

Run it now How every seam is faked Source on GitHub

What works in the tab

  • The full menu tree, exactly as on the device
  • Seed loading by QR or by hand, and passphrases
  • xpub export, PSBT loading and signing, SeedQR backup
  • Three simulated smartcards, with PINs that stick

What is not there

  • The microSD card, so settings reset on reload
  • Anything animated from a background thread
  • Timers, the screensaver, battery readings
  • Any real security. It is a tab, not a device

02 Firmware verification

Check what you flash, without opening a terminal

A SeedSigner is a Raspberry Pi with a screen. It has no secure boot and no opinion about what you put on the card, so the only thing standing between genuine firmware and tampered firmware is you, checking. The project's own instructions open by assuming you know your way around a terminal, and so most people quietly skip the step.

Drop the file onto verify.bitsaga.be instead. It computes the SHA-256 in your browser and compares it against the hash the project published. Nothing is uploaded, no cookies are set, and there is no tracking code on the page. I host no firmware at all: the download button sends you to SeedSigner's own GitHub.

It has three modes, and the difference between them is one question: who do you have to trust? Easy trusts me. Advanced trusts the SeedSigner project and shows you every value to compare. Cypherpunk trusts nobody, hands you the commands, and sells you nothing.

Open the verifier Why I built it
The verify.bitsaga.be page showing a matching hash and a green result after checking a SeedSigner firmware file

03 A chain to practise on

Rehearse a multisig with real confirmations

Behind the simulator sits Bitsaga Signet, a private Bitcoin network I run myself, with a block every thirty seconds and a faucet that always has coins. Public test networks make a poor rehearsal: slow blocks, empty faucets, and a chain that sometimes reorganises under you.

Everything else behaves like Bitcoin because the software is Bitcoin: the same node, the same addresses, the same part-signed transactions moving between a wallet and a signing device. A 2 of 3 multisig built from three simulated SeedKeeper cards, funded, signed by two of them and broadcast, confirmed in eight seconds.

The coins are not real bitcoin. They exist only on that network, cannot be sold or sent to anyone, and are worth nothing. That is the point of them.

See the network

Bitsaga Signet

Network
A custom signet, mine, always up
Block time
30 seconds
Faucet
Public, 0.01 test bitcoin per request
Addresses
testnet format, tb1...
Coin value
None, and there never will be
Open to wallets
No. The simulator reaches it from the inside

What the browser tab does not give you

A browser tab is not a hardware wallet. It has no secure element, no air gap, and it runs on a general-purpose machine next to every other tab and extension you have installed. Never type a seed phrase you rely on into the simulator, not even once, not even to check something. Use a public test seed. If you already have, treat that seed as compromised and move the funds.

Software cannot verify hardware. A perfectly checked image on a tampered board is still a tampered board, and verification says nothing about how your seed was generated. Reproducible builds push the trust boundary a very long way and they do not erase it. Anyone telling you their product achieves zero trust is selling something.

What all of it defends is one claim: that you can check I did not tamper with the firmware. Not that a browser tab is safe for your keys. I would rather say that here than have you find it out later.

“The foundation of SeedSigner's security model relies on users taking on the responsibility to ensure they are running valid software.

The SeedSigner project, on its own security model

Now pick your model

What differs between them is the screen, the case, what comes in the box, and whether your seed arrives by QR code or off a smartcard.

Packaged and shipped by me personally, from Turnhout in Belgium. Pay by card, bank transfer, bitcoin or Lightning. Questions before you buy? Reach me on the contact page.

Seedsigner plus without background
Cheapest, biggest screen

SeedSigner Plus

from€135.00VAT included

Assembled and ready to use, and the biggest screen of the family for the least money.

  • 2.8 inch IPS 240x320 screen with DPAD controls
  • USB-C port that carries power only
  • No microSD card: you flash and verify the firmware yourself
  • €10 per unit goes to the SeedSigner project maintainer
Read the full page →
SeedSigner Plus Battery Edition, orange, front
Cordless, battery powered

SeedSigner Plus Battery Edition

from€155.00VAT included

The Plus with the cable removed: three AAA batteries in the back, up to eight hours of signing, and nothing to plug in.

  • Runs on 3x AAA batteries, up to 8 hours on a fresh set
  • 2.8 inch IPS 240x320 screen with DPAD controls
  • The same stateless, air-gapped SeedSigner as the Plus
  • Assembled, or a DIY kit that costs €15 less
Read the full page →

Assembled and ready to use, or the DIY kit to build it yourself for €15 less.

Seedsigner+ with smartcard showing saved screen
PIN smartcard, no SeedQR

SeedSigner Plus Smartcard

from€200.00VAT included

Your seed lives on a PIN-protected smartcard and loads from it, so you stop handling a SeedQR every time you sign.

  • Loads keys from a Satochip SeedKeeper card, protected by a PIN
  • Cards also hold multisig descriptors and other secrets
  • 2.8 inch IPS screen, DPAD controls, USB-C power only
  • Ships with a SeedKeeper card, an 8 GB microSD and a cable
Read the full page →

One card per seed, and most buyers pick one; add more only for extra wallets or a multisig. Choose the enclosure colour, then how many cards.

SeedSigner+ Premium in a black CNC milled aluminium case, seen from above
The Plus, in aluminium

SeedSigner Plus Premium

from€225.00VAT included

The SeedSigner Plus with its printed shell swapped for a machined aluminium case, so it survives being carried.

  • CNC machined aluminium enclosure, black or orange and silver
  • Same 2.8 inch IPS screen and DPAD controls as the Plus
  • Ships with a blank microSD card, a USB-C cable and SeedQR cards
  • The card is blank on purpose: you flash and verify the firmware yourself
Read the full page →
Pick your options

Add a steel backup, or take it on its own.

Device, firmware, features: only the device changes

People compare these as if they were different wallets. They are not. Read them in three layers: the device you hold, the firmware on its microSD card, and the features that firmware gives you. Only the first layer differs on every model. The third is the same list on all of them.

ShieldSigner

CryptoGuide's smartcard fork of SeedSigner, MIT licensed

Best on SeedSigner Plus Smartcard

Your seed loads off a PIN protected Satochip SeedKeeper card. Scanning a SeedQR still works, so you keep both routes.

Everything the stock firmware does, and a long list on top of it: the whole smartcard suite, SLIP39, encrypted QR codes, and more entropy checking. The table below is the full comparison.

Read the source

Free, no purchase Run both firmwares in your browser The real code, running in your browser, with a toggle between SeedSigner and ShieldSigner. Load a seed, sign a transaction, see which one you actually want. Before you flash Check a firmware file yourself Drop the image on the page. It computes the SHA-256 in your browser and compares it with the hash the project published. Both firmwares are covered, and nothing is uploaded.

Layer one, the device

From the product data and from the units I package and ship myself. Every one of them is the same Raspberry Pi Zero 1.3 with no wifi and no bluetooth on it.

Show the full hardware comparison
SeedSigner hardware specifications, model by model
 SeedSigner Plus SeedSigner Plus Battery Edition SeedSigner Plus Smartcard SeedSigner Plus Premium
Best firmware for itAny of them boots either firmware, it is only a different microSD card. But only the smartcard model has the card reader, so on the other models the whole smartcard half of ShieldSigner has nothing to talk to.SeedSignerSeedSignerShieldSignerSeedSigner
Core boardVersion 1.3 is the Pi Zero with no wifi and no bluetooth on the board. The project specifies it for exactly that reason, and every model here uses it.Raspberry Pi Zero 1.3Raspberry Pi Zero 1.3Raspberry Pi Zero 1.3Raspberry Pi Zero 1.3
Screen2.8 inch IPS, 240x3202.8 inch IPS, 240x3202.8 inch IPS, 240x3202.8 inch IPS, 240x320
ControlsDPAD style buttonsDPAD style buttonsDPAD style buttonsDPAD style buttons
CameraZeroCamZeroCamZeroCamZeroCam mini
EnclosureThe aluminium version of the smartcard build is not available yet.3D printed shell3D printed shell, battery compartment in the back3D printed shellCNC machined aluminium
ColourOne versionOrangeBlack or orangeBlack, or orange and silver
Power portPower only means power only. Nothing but power goes down that cable, so there is no data path on it to take on trust.USB-C, power onlyNone, it runs on batteriesUSB-C, power onlyUSB-C, power only
Spring loaded microSD slotYesYesYesYes
Smartcard readerNoNoYes, a smartcard hat and a Satochip SeedKeeper cardNo
Wifi or bluetoothNone, on any of themNot statedNone, on any of themNone, on any of them
BatteryNone, it runs off the cable3x AAA, up to 8 hours on a fresh setNone, it runs off the cableNone, it runs off the cable

Layer two, the firmware

ShieldSigner does everything SeedSigner does. All of it. It is a fork, not an alternative, and nothing was taken out.

So the only useful table is the one below: what the fork adds on top. Both are MIT, both are free, and both run on any of them. Taken from the two projects' own READMEs, not from me.

Show the full firmware comparison
Where the ShieldSigner smartcard fork differs from SeedSigner
  SeedSignerthe project's own firmware ShieldSignerCryptoGuide's smartcard fork
Getting a seed onto it
Seed word lengths12 or 2412, 15, 18, 21 or 24
Load a seed off a Satochip SeedKeeper cardNoYes
Load a passphrase, or seed and passphrase together, off a cardNoYes
SLIP39 shares: create, import, extend and reconstructNoYes
BIP85 child seedsDerive themDerive and load them
Encrypted QR codes, Krux compatibleNoYes
Passphrase QR, plaintext QR export, and a TextQR toolNoYes
Split passphrase and encryption key across two QR codesNoYes
Signing and wallets
Save and load multisig descriptors on a cardNoYes
Verify a wallet xpub exportNoYes
Sign a transaction on the card itself, and verify a PSBT against itNoYes
Sign a messageNoYes
WIF and BIP38 key signingNoYes, and off by default
The cards themselves
Card readers it speaks toNoneSmartcard hat over UART, USB CCID and PCSC, PN532 over NFC, USB Phoenix
Initialise a card, change its PIN, label it, set its NFC policyNoYes
Factory reset a card, read its info, check it is genuineNoYes
Satochip two factorNoYes
Store any secret on a card, and read it back as text or a QR codeNoYes
Entropy and housekeeping
Shannon entropy checks on dice and camera inputNoYes
Hardware RNG mixed into camera entropy, with a quality readoutNoYes
Optional wipe timerNoYes, 30 minutes
GPG signature and SHA256 manifest checking on the deviceNoYes
microSD flashing and verification tools on the deviceNoYes
What you are trusting
Who publishes itThe SeedSigner projectCryptoGuide, as 3rdIteration
LicenceMITMIT
Maturity, in the project's own wordsStable releasesBeta: "mostly feature complete", with "bugs and tweaks to come"
Covered by verify.bitsaga.beYes, check a fileYes, check a file
Runs in the browser simulatorYes, run it nowYes, run it now

Only the differences are listed. A further 17 features are identical on both and are left out. 21 rows here the fork adds on its own.

What's in the box, and what you pick at checkout

The parcel and the checkout, not the machine. The machine is the table above.

What arrives, and what you choose at checkout
 SeedSigner Plus from €135.00 to €150.00SeedSigner Plus Battery Edition from €155.00 to €170.00SeedSigner Plus Smartcard from €200.00 to €340.00SeedSigner Plus Premium from €225.00
microSD card includedNoYes, 8 GBYes, 8 GBYes, blank
Also in the boxUSB-C cable, 25x25 SeedQR cardsBatteries are not includedUSB-C cableUSB-C cable, 25x25 SeedQR cards
Try this one in the simulatorPick the stock firmwarePick the stock firmwareThe default, smartcard firmwarePick the stock firmware
Choices at checkoutNone, one versionAssembled, or a DIY kit for €15 lessColour, and 1 to 5 SeedKeeper cardsEnclosure colour

Prices are live from the catalogue.

Neither firmware is mine

The full feature comparison is the second table above. This is who wrote them.

SeedSigner is open source under MIT, built by volunteers. ShieldSigner is CryptoGuide's fork of it, also MIT, and it is the one that speaks to the smartcards. I package and ship the hardware. I wrote neither firmware, and I am not the person to ask whether they are honest: read them yourself, or rebuild one and check the image I ship against your own build. €10 from every assembled unit goes to the SeedSigner project's lead maintainer.

The SeedSigner project SeedSigner on GitHub ShieldSigner on GitHub Verify a firmware file Run it in your browser

Questions

The ones I actually get asked, answered without the sales voice.

Is my seed stored on the device?

No. A SeedSigner is stateless: the seed sits in memory only while the device has power, and it is gone when you unplug it. There is no key material on the device for anyone to find later. The smartcard model changes where the seed comes from, not where it lives: it loads from a PIN-protected SeedKeeper card into the same temporary memory.

Which model should I buy?

If this is your first air-gapped device, the SeedSigner Plus: it is the cheapest, it has the largest screen, and everything you need is in the box. If you will sign often and do not want to handle a SeedQR every time, the SeedSigner Plus Smartcard. If you want a metal case, the SeedSigner Plus Premium.

Which wallet software does it work with?

Any coordinator that speaks QR. Sparrow, Specter Desktop, Nunchuk, BlueWallet and Keeper are the usual ones. You keep watching your balance there. Only the signing happens on the device.

Can I really try it before buying?

Yes, and it costs nothing. The simulator runs the real firmware in a browser tab, so you can walk the menus, load a seed, add a passphrase, export an xpub and sign a transaction before anyone asks you for money. Use a public test seed, never one of your own.

Is the simulator the same as owning the device?

No, and it is not meant to be. It proves the flows and the firmware, not the security: a browser tab has no secure element and no air gap. The full list is in the article about it.

Do I have to verify the firmware myself?

You should, and it is the one step most people skip because the official instructions assume a terminal. verify.bitsaga.be does the same check by dropping the file onto a page: it computes the SHA-256 in your browser and compares it against the hash the project published. The file never leaves your computer, and I host no firmware at all.

Can one device do multisig?

Yes, and it is the cheapest honest way to try it. Load your seeds one at a time, export each xpub to your coordinator, and sign each key on the same device. If you want to rehearse the whole thing first, the simulator plus my signet gives you a 2 of 3 that actually confirms.

What about VAT and shipping?

Every price on this page includes VAT. Shipping is calculated at checkout from your address, and you can pay by Bancontact, bank transfer, bitcoin or Lightning, card, PayPal, Google Pay or Apple Pay.

If you would rather read first

TechnicalRun the real SeedSigner firmware in your browserEvery faked seam, what you can verify yourself, and why you must never type a real seed into it.SecurityVerifying SeedSignerWhy the verification step gets skipped, what I built instead, and the part where I tell you not to trust it.TechnicalSeedSigner is the Bitcoin Swiss army knifeStateless signing, dice or photo entropy, and the cheapest honest way to try multisig.RepublishedThe DIY signing device revolution is just beginningKeith Mukai's report from the São Paulo summit, republished in full with my notes.

Try it first. Then decide.

It costs nothing to find out whether you like the device, and I would rather you knew before the parcel arrives than after.

Run one in your browser Pick a model

The simulator and the verifier are independent projects, MIT licensed, not affiliated with or endorsed by the SeedSigner project. Product photographs and specifications come from my WooCommerce catalogue.

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