Mobile phone app (iOS)

The NBT Pass-Through (PT) mobile phone app (view on GitHub) is a Swift-based Xcode project which showcases the OPTIGA™ Authenticate NBT in the host parameterization via pass-through (PT) use case.

Installation

Instructions to build the app and install it on an iOS device can be found in the README file of the GitHub repository (view on GitHub).

Software architecture

The application is structured using the MVVM (Model-View-ViewModel) pattern and utilizes the modules of the OPTIGA™ Authenticate NBT Host Library for Swift. The library modules are included in the Libraries/optiga-nbt-lib-swift folder and added as dependencies to the Xcode project.

Fig. 92 High-level software architecture of the iOS app.

Components

1. Mobile application:

   • PTModeView: Displays the main interface for controlling the LED state.

   • PtUseCaseManager: Manages the pass-through use case logic, including LED state updates and communication with the host device.

   • PTViewModel: Handles the business logic for the PT use case, including user interactions and data binding.

2. OPTIGA™ Authenticate NBT host library (in Libraries/optiga-nbt-lib-swift):

   • CommandSet: APIs for sending APDU commands.

   • CommandBuilder: Constructs APDU commands.

   • ResponseParser: Parses responses from the NFC tag.

3. Communication channel:

   • NfcChannel (from Libraries/InfineonChanneliOSNfc): Implements the communication interface for NFC using Core NFC.

   • NFCSessionManager (in Services/): Manages Core NFC sessions and tag communication.

Application flow

The first and only view to be started is the PTModeView(), where the user can control the LED button.

To write to the host device, the user needs to set the desired state of the LED using the LED button in the GUI and tap the antenna of the OPTIGA™ Authenticate NBT device to the mobile phone. The detection of the NFC tag will trigger a cascade of commands that are handled in the methods of the PtUseCaseManager class.

PtUseCaseManager() will:

1. Select the proprietary demonstrator application on the host device

2. Write the LED state into the host application using a simple proprietary command

Fig. 93 Visualization of the app’s views during operation.

Application details

The application is developed using Xcode and follows the standard iOS project structure.

Project layout

The project is structured as a standard Xcode project with a modular folder layout:

Listing 51 Project layout (simplified).

optiga-nbt-example-pt-ios/
├── docs/                            # Documentation and images
├── InfineonNBTPT/                   # Main app target
│   ├── Business/                    # Business logic and view models
│   ├── Presentation/                # SwiftUI views, assets, and resources
│   ├── Services/                    # Service classes (e.g., NFC, logging)
│   ├── InfineonNBTPT.entitlements   # App entitlements
│   └── InfineonNBTPT.plist          # App configuration
├── LICENSES/                        # License files
├── Libraries/                       # External and internal library modules
│   ├── InfineonChanneliOSNfc/       # Infineon NFC channel library for iOS
│   ├── InfineonConsoleLogger/       # Infineon console logger library
│   └── optiga-nbt-lib-swift/        # OPTIGA™ Authenticate NBT Host Library for Swift
├── InfineonNBTPT.xcodeproj/         # Xcode project file
├── LICENSE                          # License information
└── README.md                        # Project documentation

Project configuration

This can be done in the project settings in Xcode:

• Deployment Target: Set to iOS 15.0 or later.

• Swift Language Version: Set to Swift 5.0 or later.

• Signing & Capabilities: Ensure the app has the necessary entitlements for NFC access.

Integration of the Swift host library

The OPTIGA™ Authenticate NBT Host Library for Swift is included in the project as a module. The library provides the necessary APIs for sending APDU commands to the OPTIGA™ Authenticate NBT device. The library is located in the Libraries/optiga-nbt-lib-swift folder and is added as a dependency in the Xcode project. The app uses the library’s APIs to construct and send APDU commands, handle responses, and manage NFC communication. The library is structured into several modules, including:

• CommandSet: Contains APIs for sending APDU commands to the OPTIGA™ Authenticate NBT device.

• CommandBuilder: Provides methods to construct APDU commands.

• ResponseParser: Parses responses from the OPTIGA™ Authenticate NBT device.

Usage of NFC in the app

The app uses Core NFC to communicate with the OPTIGA™ Authenticate NBT device. NFC sessions are managed by the NFCSessionManager class in the Services layer, using NFCNDEFReaderSession and NFCISO7816Tag for APDU-level communication.

NFC Capability enabled in Xcode:

In your Xcode project, select your target → Signing & Capabilities tab → click + Capability → add Near Field Communication Tag Reading.

NFC Usage Description:

To comply with App Store guidelines, you must provide a usage description for NFC in your app’s Info.plist file. This informs users why your app needs access to NFC functionality. To add the NFC usage description, you can either edit the Info.plist file directly or use Xcode’s property list editor. The key is NFCReaderUsageDescription, and the value should be a string explaining why your app uses NFC. To add the NFC usage description in the Info.plist file, you can use the following XML snippet:

Listing 52 Project layout.

<key>NFCReaderUsageDescription</key>
<string>This app uses NFC to communicate with the OPTIGA Authenticate NBT device.</string>

This can also be specified in the Xcode project settings.

NFC Entitlement in .entitlements file

To enable NFC functionality, the app must have the appropriate entitlements. The following key is added to the InfineonNBTADT.entitlements file: This enables NFC hardware access at the system level.

Listing 53 Add NFC entitlement.

<key>com.apple.developer.nfc.readersession.formats</key>
<array>
   <string>TAG</string>
</array>

Listing 54 Add NFC entitlement for ISO7816 tags with the the NFC Type 4 Tag application ID (AID).

<key>com.apple.developer.nfc.readersession.iso7816.select-identifiers</key>
<array>
   <string>D2760000850101</string>
</array>

This entry allows your app to use Core NFC to select and communicate with ISO7816 tags that have the specified AID (D2760000850101).

Session handling:

NFC sessions in the iOS app are managed by the NFCSessionManager class, located in InfineonNBTADT/Services/NFCSessionManager/NFCSessionManager.swift.

• NFCSessionManager implements the NFCTagReaderSessionDelegate protocol.

• When an NFC operation is required (e.g., the user selects “Read” or “Write”), the app calls startNFCTagReaderSession(withAlertMessage:):

  • Creates a new NFCTagReaderSession for ISO14443 tags.

  • Sets the delegate to NFCSessionManager.

  • Starts the session with .begin() and displays an alert message to the user.

• When a tag is detected, the delegate method tagReaderSession(_:didDetect:) is called:

  • A NfcChannel is created for the tag and session.

  • The channel is wrapped in an ApduChannel and a NbtCommandSet is created.

  • The app connects to the tag, selects the application, and executes the ADT use case logic (read or write).

• If the session is invalidated (e.g., user cancels or an error occurs), tagReaderSession(_:didInvalidateWithError:) is called:

  • The session is cleaned up.

  • The UI is updated with the appropriate state or message.

• Session state and messages are published using @Published properties, allowing the UI to react to changes.

Related resources

• NFC overview on developer.apple.com

• GitHub repository of this app