Daily Tech Observations 6

Google Community Mobility Reports

The latest report was released on April 16th. On top of the individual PDF files for each country you also can download a CSV file with all the data. With the CSV file at hand it is easier to compare countries or regions against each other and detect when lockdown came in place etc. Time to spin up your favourite visualization tool or for some hands-on Pandas-Bokeh action.

Tracing Apps

Despite announcing the release of such an app after Easter, there is nothing released yet. It is a challenge to release such an app, once pushed out to public you cant reverse or make significant changes to the key exchange algorithm etc. The rotating key mechanism need to be waterproof to avoid any tracking or identifying of persons just by looking at the local data storage and ‘wardriving’. Personally I believe no one want to do another quick shot like the ‘Datenspende-App’ (see next topic) and stay compliant with the below requirements. I highly recommend to read the read the contact-tracing-apps requirements by..

At all cost privacy has to be protected and we do not want any contact tracing in any non-health related crisis situations, eg. to be used to trace contacts in recent Hong-Kong events or during the Arab Spring in 2010.

I am very curious if and how they will release the source code for such an app.

Datenspende App

The RKI released the Datenspende app using anonymously health data from smart watches etc. (see previous post). Unfortunately they triggered a partially controversial discussion in media due to the fact that the usage of the data was not stated clearly enough, the app is implemented as closed-source by an external company and a few other problems like the lack of support of many health trackers. This resulted in quite a number of 1* ratings (refer to AppBrain). Though I absolutely believe in their good intentions and the good use of the data, RKI just had a bad start with this.

AppBrain Statistics

Google cooperating with Apple

Certainly makes most sense to have the same API features on OS level, though I am not sure how to publish this. Through an OS Update ? Here we would rely on the mobile phone manufacturers, quite a large number of phones have fallen out of the support cycles. Have a look at the specifications at the Apple website.

DIY Project: Create a Tracking App Part 1

The discussion about mobile phone location tracking of people and tracing back to potential transmissions is one of the hot topics at moment. In Germany we could expect an app officially being launched towards end of April. I attempt to go through the technical considerations by myself. A hands-on coding excursion with Android to use Bluetooth to scan nearby devices and exchange data with them.

The most basic requirements for a tracking app to be successful:

  • A person need to posses and carry a switched-on mobile (smart) phone.
  • The phone must have GPS and Bluetooth feature and both being enabled.
  • The location need to be recorded as fine-grain as possible. Use of GPS is mandatory, the celldata is way too coarse (see previous post). Though we might consider to skip location completely and rely on the paring of fingerprints solely, depending on the approach.
  • Approach 1: We record the location and time of a device (aka person) and transmit the data to a server immediately and try to match data with other devices on the server. Hard to implement in a GDPR compliant way and users most likely wont buy in.
  • Approach 2: We record the location and time on the device and any digital fingerprint of devices nearby. This anonymous pairings we transmit to the server. Once one device is flagged as infected, the server can flag any other device “paired” previously and push (or pull) a notification to the impacted devices. This way most data remains on the device. A more GDPR compliant way of solving this. Some details need to be worked out though in regards of matching and informing the respective user.
  • Approah 3: Even better if we could rely solely on the fingerprint of nearby devices and the timestamp.
  • The more user we have in the system, the bigger the impact and the chance to trace and inform and potentially stop spreading further.
  • We must have a mean to report an infection and inform affected other users (and still stay within the boundaries of GDPR).

Before walking into the Bluetooth space, some facts:

  • The not-for-profit organisation Bluetooth Special Interest Group (SIG) is responsible for thedevelopment of Bluetooth standards since 1998. (Wikipedia)
  • There is a regular update to the Bluetooth standard, by January this year SIG released version 5.2. It takes time for the hardware manufacturers to adopt the newer standards.
  • We need to distinguish between Bluetooth Classic and Bluetooth Low Energy (BLE). BLE was introduced with version 4 and supported by Android 4.3.
  • Bluetooth Classic is designed for continous short distance two-way data transfer at a speed of up to 5 Mbps (2.1 Mbps with Bluetooth 4). BLE was made to work with other devices at a lower speed and greater distance.
  • Android 8.0 onwards support Bluetooth 5 which is a significant milestone for Bluetooth technology in terms of range, speed and power consumption.
  • It is not possible to programmatically check the supported Bluetooth version in Android, though you can check if BLE is available on the phone.
  • The MAC address of the Bluetooth adapter is fixed and can’t be changed (except for rooted phones). This way it becomes the digital fingerprint.

Are we running out of MAC addresses ?

MAC addresses (used by ethernet, wifi and bluetooth adapters), as per IEEE 802 definition, have 48 bits (6×8 bytes).
Sample AC:07:5F:F8:2F:44
This would result in some 281 trillion (2^48) possible combinations, but the first 3 bytes are reserved to identify the hardware manufacturer. For above sample AC:07:5F it is Huawei. The remaining 3 bytes are used as unique identifier, resulting in only 16 million (2^24) unique devices. Quite likely this number would be used up more or less quickly by a big manufacturer. In reality we also could have 16 million unique manufacturer ID’s, Huawei owns about 600 of these, giving a total of currently 10 billion devices. We need to consider this numbers when we talk about unique fingerprints (MAC), though it is unlikely at a country level to have duplicates. In Germany we have ~83 million citizens and about 142 million mobile phones from different manufacturers, small chance that two persons (actually using the tracking app) will have the same MAC address.
You can check/download the identifiers here.

Lets get started with some coding..

Basic: Android to list paired devices

Before we jump into the more complex discovering, pairing and communication between devices (using threads,) we start with the basics. Lets enumerate the paired devices.

Required Permission

At minimum access to coarse location (since Android 6) is needed since Bluetooth can be used to derive the users location. I skip the code to request the permission, only location access being a critical permission. (complete code will be pusblished at the end).

<uses-permission android:name="android.permission.BLUETOOTH"/>
<uses-permission android:name="android.permission.BLUETOOTH_ADMIN"/>
<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />

Check and Activate Bluetooth Adapter

public class MainActivity extends AppCompatActivity {

    private static final String TAG = "bt.MainActivity";
    private BluetoothAdapter bAdapter = BluetoothAdapter.getDefaultAdapter();

    protected void onCreate(Bundle savedInstanceState) {


            Log.i(TAG,"Bluetooth not supported.");
        } else {
            Log.i(TAG,"Bluetooth supported.");
				Log.i(TAG,"Bluetooth enabled.");
				if (!getPackageManager().hasSystemFeature(PackageManager.FEATURE_BLUETOOTH_LE))
					Log.i(TAG, "BLE not supported.");
					Log.i(TAG, "BLE supported.");
			} else {
				Log.i(TAG,"Bluetooth not enabled.");
				startActivityForResult(new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE),1);

List existing pairings

Quite simple to iterate through the existing pairings and list their name and MAC Address

private void showPairedDevices(){
	Set<BluetoothDevice> pairedDevices = bAdapter.getBondedDevices();
	if (pairedDevices.size() > 0) {
		for (BluetoothDevice device : pairedDevices) {
			String deviceName = device.getName();
			String deviceMAC = device.getAddress();
			Log.i(TAG,"Device: " + deviceName + "," + deviceMAC);
I/bt.MainActivity: Device: HUAWEI P20,AC:07:5F:XX:XX:XX
I/bt.MainActivity: Device: moto x4,0C:CB:85:XX:XX:XX

In the next post we will discover nearby Bluetooth devices and setting up a communication channel between two devices.

Stay tuned for more tracking..


Image by Brian Merrill from Pixabay