What is BoB standard?

Introduction to BoB standard by Samtrafiken

What is this library for?

Standard defines that mobile ticket bundles (MTB-s) are signed both by issuer and the device itself. This helper library helps to construct device signed ticket bundles for Android devices more easily. Also this library can be used as a research basis for BoB standard in general as there are not many actual implementations that developers can use for examples.

Using library

This library is not (yet) published to any remote repositories, so first step is to actually checkout the code.

git clone https://github.com/tanieltari/bob-mtb.git

After checkout one must use platform specific Gradle wrapper script to run task called publishToMavenLocal

# Windows users
.\gradlew.bat publishToMavenLocal
# *nix users (Linux, MacOS etc)
./gradlew publishToMavenLocal

This will build the AAR file and publish it to the local Maven repository (~/.m2 directory)

API

Device ID (used in bundle header & to retrieve device key)

Content resolver can be retrieved only from inside Activity

DeviceService deviceService = new DeviceService();
String deviceId = deviceService.getDeviceId(getContentResolver());

Device current timestamp (used in bundle header)

DeviceService deviceService = new DeviceService();
String deviceDateTime = deviceService.getDeviceDateTime();

Device key (for signing bundle)

Retrieving the authentication token from BoB Authentication API is developer responsibility

DeviceClient deviceClient = new DeviceClient();
DeviceKeyResponse deviceKeyResponse = deviceClient.getDeviceKey("https://device.bob.example.com/api/v1/device/key", deviceId, authToken);

Device bundle header

Must define at least key, algorithm and device ID as defined in the standard

DeviceBundleHeader deviceBundleHeader = new DeviceBundleHeader();
deviceBundleHeader.setKeyId(deviceKeyResponse.getKeyId());
deviceBundleHeader.setAlgorithm("HS256");
deviceBundleHeader.setDeviceId(deviceId);
deviceBundleHeader.setTimestamp(deviceDateTime);
/* ... */

Compressor service

CompressorService compressorService = new CompressorService();
try {
    byte[] compressedBytes = compressorService.compressBytesZlib(new byte[] {1, 2, 3});
} catch (IOException e) {
    // Handle exception
}
try {
    boolean isZlibBytes = compressorService.isZlibCompressed(new byte[] { 1, 2, 3 });
} catch (IOException e) {
    // Handle exception
}

MTB service

Last boolean in the method definition tells if MTB should be compressed or not

MtbService mtbService = new MtbService(compressorService);
try {
    String issuerSignedMtb = mtbService.createDeviceSignedContainer(issuerMtb, deviceBundleHeader, deviceKeyResponse.getKey(), true);
} catch (IOException e) {
    // Handle exception
}

Aztec barcode service

Last integer in the method definition tells what ECC (error code correction) percentage should be used

AztecBarcode aztecBarcode = new AztecBarcode(compressorService);
try {
    Bitmap mtbAztec = aztecBarcode.generateMtbBarcodeBitmap(issuerSignedMtb, 23);
} catch (IOException e) {
    // Handle exception
}