NFC Demo – Android App

NFC Demo is an Android-only application for experimenting with NFC smart cards. It provides four main “pages” (screens), each tailored to a specific aspect of NFC development and testing:

  1. Raw APDU Terminal
    Send and receive low-level APDU commands directly to/from an NFC card.
  2. Lin Interactive Terminal
    A REPL-style interface powered by the custom Lin scripting language, letting you send APDU commands, parse responses, and incorporate logic on the fly.

    For more information on Lin, see the Lin-language GitHub repo.

  3. Lin Script Builder
    A full‐featured script editor where you can compose, and run multi‐line Lin scripts that interact with NFC cards.
  4. TLV Parser / Tree Viewer
    Feed a hex-encoded TLV response into a parser and view it as a nested, ASCII-art tree. (You can also pipe APDU responses from the Raw Terminal into this page.)

Key Facts

  • Platform: Android only (no iOS or desktop support at present).
  • Architecture: Built with .NET MAUI for Android.
  • Pages / Screens:
    1. NFC Terminal (Raw APDU)
      • Text‐based terminal (90% of the screen) for typing APDU hex commands.
      • A “Send” button to push the selected APDU to the card.
      • Scrollable output area showing card responses (status words + data).
    2. Lin Interactive Terminal
      • REPL prompt for Lin language commands.
      • Built-in Lin functions include print, apdu(...), tlv(...), tree(...), etc.
      • On each apdu(...) call, Lin will send the hex command to the card and display the response.
      • Colors, error reporting, and simple script fragments can be tested here.
    3. Lin Script Builder
      • Simple multiline code editor.
      • “Run” button at the top.
      • Output area at the bottom, similar to the interactive terminal.
    4. TLV Parser / Tree Viewer
      • Paste or pipe a hex string (e.g. an APDU response) into the input area.
      • Instantly parses Tag-Length-Value structures.
      • Displays a nested tree in ASCII-art format, showing tags, lengths, values, and hierarchy.

Getting Started

  1. Install & Run (Android only)

    • Clone or download this repository.
    • Open in Visual Studio 2022/2023 with .NET MAUI workload installed.
    • Ensure your Android SDK minimum target is set to API 21 or higher.
    • Deploy to a physical Android device (with NFC) or emulator (requires NFC passthrough).

  2. Permissions

    • The app requires <uses-permission android:name="android.permission.NFC" /> in the generated manifest.
    • Make sure NFC is enabled on your device.

  3. Usage Overview

    • Raw APDU Terminal:
      1. Launch the “NFC Terminal” page.
      2. Type a hex APDU (e.g. 00A4040007A0000002471001).
      3. Tap Send.
      4. View the card response.
    • Lin Interactive Terminal:
      1. Open “Lin Terminal.”
      2. At the prompt, type apdu("00A4040007A0000002471001") → returns a hex string.
      3. Try print("Hello, NFC!") or printc("#00FF00", "OK").
      4. Combine logic: 
        resp = apdu("00B0950000")
if(find(resp, "9000") >= 0){
   printc("#00FF00", "Success:", resp)
} else {
   error("Card returned error:", resp)
}
    • Lin Script Builder:
      1. Navigate to “Script” page.
      2. Write a multi-line script, for example: 
        // Select PSE
sel = apdu("00A404000E315041592E5359532E4444463031")
print("Select PSE", sel)

// Parse TLV and display hierarchy
t = tlv(sel)
print(tree(t))

// Read record 1
rec = apdu("00B2010C00")
print("Record 1", rec)
      3. Tap Run to execute the entire script at once. Output appears below.
    • TLV Parser / Tree Viewer:
      1. Go to “TLV” page.
      2. Paste a hex string (e.g. 6F10840A325041592E5359532E4444463031A5048801020046...).
      3. The app will automatically parse and display: 
        └─ 6F
   ├─ 84 : 325041592E5359532E4444463031
   └─ A5
      ├─ 88 : 010200
      └─ 46 : 6F6368657343617264
      4. You can also pipe the APDU response from the Raw Terminal.

License & Contributions

This project is released under the MIT License. Contributions are welcome:

  • Fork the repository, make your changes, and open a pull request.
  • Report issues or feature requests via Issues on GitHub.

Enjoy experimenting with NFC, APDUs, Lin scripting, and TLV parsing!

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