bitPOS Card Writer

Android app for programming and wiping NTAG 424 DNA Bolt Cards. Part of the bitPOS open-source Lightning payments platform.

---

Download

Download bitPOS-Card-Writer.apk

Install steps

1. Download the APK on your Android device
2. Go to Settings - Security - Install unknown apps and allow your browser or file manager
3. Open the downloaded APK and tap Install
4. Launch bitPOS Card Writer

---

What it does

Screen	Action
Write	Paste a bitPOS provision URL, hold card to phone - card is programmed as a working Bolt Card
Wipe	Paste the wipe JSON from bitPOS, hold card to phone - card is reset to factory defaults

Requirements

• Android phone with NFC
• NTAG 424 DNA card (standard Bolt Card blank)
• A running bitPOS instance

---

How it works

The app implements the full NTAG 424 DNA APDU sequence over NFC:

1. AuthenticateEV2First - AES-128 mutual authentication with the card
2. ChangeKey x5 - Programs k0 (app master) and k1-k4 (Bolt Card CMAC keys)
3. ChangeFileSettings - Enables SDM (Secure Dynamic Messaging) with LNURL-W parameters
4. WriteBinary - Writes the NDEF record containing the LNURL-W URL

All key material is fetched from the bitPOS API at provision time. Nothing is stored on the device.

---

Build from source

Requirements: Node 20+, pnpm 9+, Expo CLI, Android phone with USB debugging or EAS account

git clone https://github.com/satosys-tech/bitpos-card-writer.git
cd bitpos-card-writer
pnpm install

# Run in Expo Go (development)
cd artifacts/card-writer
pnpm exec expo start --localhost

# Build APK via EAS cloud (requires free EAS account)
pnpm exec eas build --platform android --profile preview

EAS setup (first time)

pnpm exec eas login
pnpm exec eas build:configure

---

Project structure

artifacts/card-writer/
  app/
    (tabs)/
      index.tsx      # Write screen
      wipe.tsx       # Wipe screen
  utils/
    ntag424.ts       # NTAG 424 DNA APDU sequences
    crypto.ts        # AES-128 primitives (crypto-js)
    cmac.js          # AES-CMAC (artjomb extension)
    ndef.ts          # NDEF builder + SDM offset computation

---

Contributing

Pull requests welcome. The core NFC logic is in artifacts/card-writer/utils/ntag424.ts.

---

License

MIT