> ## Documentation Index
> Fetch the complete documentation index at: https://docs.zerokeyusb.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Bitcoin Wallet

> Create an airgapped Bitcoin wallet on the device, export a watch-only key to your phone, and sign transactions (PSBT) — the private key never leaves the device.

ZeroKeyUSB can act as an **airgapped Bitcoin signer**. The wallet is a standard **BIP84 native SegWit** wallet (`m/84'/0'/0'`, `bc1q…` addresses). The 12-word seed is generated **on the device** from the ATECC608A hardware TRNG, stored AES-encrypted, and shown **only on the OLED** — it never leaves over USB. You watch balances and build transactions on a separate wallet (phone/desktop); the device only ever reveals **public** data (the `zpub`) and **signatures**.

<Note>
  Find the Bitcoin menu under **Tools → Bitcoin**. Mainnet only.
</Note>

| Menu item         | What it does                                                         |
| ----------------- | -------------------------------------------------------------------- |
| **Show seed**     | Re-displays the 12 words on the OLED (screen only)                   |
| **Watch-only**    | Prints the `zpub`, master fingerprint and `wpkh` descriptor over USB |
| **Create wallet** | Generates a new 12-word seed (overwrites any existing one)           |

***

## 1 · Create the wallet

<Steps>
  <Step title="Open Tools → Bitcoin → Create wallet">
    If a wallet already exists, the device asks you to **hold Center** to confirm the overwrite (this **destroys** the old seed). On a fresh device it starts straight away.
  </Step>

  <Step title="Write the 12 words on paper">
    The device shows the words in pages of three. Advance by tapping. **Write them on paper only** — never photograph them or type them into a computer.
  </Step>

  <Step title="Store the paper safely">
    Anyone with these 12 words controls the funds. The device keeps the seed encrypted; the paper is your only backup.
  </Step>
</Steps>

<Warning>
  **Create wallet** generates a brand-new random seed and overwrites the previous one. Coins on the old wallet are lost unless you backed up its 12 words.
</Warning>

You can re-check the words any time with **Show seed**.

***

## 2 · Set up a watch-only wallet (phone/desktop)

To see balances and build transactions you import the **public** account key into a normal wallet (BlueWallet, Nunchuk, Sparrow, Bitcoin Core…). The device exposes it as a `zpub` and a `wpkh` descriptor with the master-key origin — the origin is required so the transactions you build are recognised by the signer.

<Steps>
  <Step title="Open the Bitcoin webtool">
    Open `bitcoin.html` in Chrome or Edge (Web Serial), **Connect device**, and unlock the device with your PIN.
  </Step>

  <Step title="Get watch-only from device">
    Press **Get watch-only**. The page shows the fingerprint, `zpub` and the full descriptor `wpkh([FP/84h/0h/0h]zpub…/0/*)#checksum`, plus a **QR code**.
  </Step>

  <Step title="Scan into your wallet">
    Scan the **descriptor QR** (or the `zpub` QR) into your mobile wallet. It can now show balances and create transactions, but it cannot spend — it has no private key.
  </Step>
</Steps>

<Tip>
  You can also trigger the export from the device itself: **Tools → Bitcoin → Watch-only** prints the same data over the serial connection.
</Tip>

***

## 3 · Sign a transaction (PSBT)

The flow is the standard airgapped PSBT flow: build the spend on your watch-only wallet, sign it on ZeroKeyUSB, then broadcast from the wallet.

<Steps>
  <Step title="Build the spend">
    In your watch-only wallet, create the transaction and **export the unsigned PSBT** (base64).
  </Step>

  <Step title="Send it to the device">
    In `bitcoin.html`, paste the PSBT and press **Send to device**.
  </Step>

  <Step title="Verify ON THE DEVICE">
    The OLED shows the destination, the amount being sent and the fee. **Verify these on the device screen**, not in the browser.
  </Step>

  <Step title="Hold Center to sign">
    Hold **Center** to sign (a progress border fills around the screen). Tap any other button to cancel. The device returns the **signed PSBT** to the webtool.
  </Step>

  <Step title="Broadcast">
    Copy the signed PSBT back into your wallet, finalise and broadcast.
  </Step>
</Steps>

<Warning>
  Always confirm the **address and amount on the device's own screen** before holding to sign. A compromised computer can show you one thing in the browser while sending another — the device screen is the trusted display.
</Warning>

If the PSBT has no inputs belonging to this wallet, the device replies **"No inputs for us"** and signs nothing — that is expected when the PSBT is for a different wallet.

***

## Security model

* The **seed never leaves** the device over USB. It is shown only on the OLED, and stored AES-encrypted (same key as your credentials, protected by your PIN).
* Only **public** data (`zpub`, descriptor) and **signatures** are sent over USB.
* Signing requires a deliberate **Center hold** after on-screen review — never blind-signs.
* Entropy comes from the **ATECC608A hardware TRNG**; the device refuses to generate a seed if the hardware RNG check fails.
* The wallet is **BIP84 mainnet** (`m/84'/0'/0'`).

<CardGroup cols={2}>
  <Card title="Navigate the menu" icon="bars" href="/getting-started/menu-navigation">
    Where to find Tools → Bitcoin.
  </Card>

  <Card title="Broken / no screen" icon="eye-low-vision" href="/getting-started/recovery-no-screen">
    Recover access if the display fails.
  </Card>
</CardGroup>