The truth about decentralized contact tracing apps like Immuni

Lees dit artikel in het Nederlands: De waarheid over gedecentraliseerde contact tracing apps zoals Coronalert

Too long to read? Skip to the conclusion.

Table of contents

Those that know me a bit, know that I think that privacy is very important. For this reason when they started talking about contact tracing apps for COVID-19 a few months ago, I thought this was an extremely bad idea. Having an app constantly tracking where you are and who you meet, is only something which you think is possible in undemocratic nations and dictatorial regimes. Something you expect in North Korea, China but not in European countries, where our privacy is supposed to be protected by the GDPR. And then what about the reliability of these apps? Bluetooth was never made for this. It would result in many false positives and negatives. No way I would ever install such an app.

That was at least my opinion a couple of months ago. Now my opinion about this matter has completely changed. Reading about decentralized solutions based on the Google and Apple Exposure Notification (GAEN) API and DP-3T, has completely changed my mind. I use the Italian contact tracing app Immuni and I am willing to use a similar decentralized app from any country where I am staying.

DP-3T

Decentralized Privacy-Preserving Proximity Tracing or DP-3T is an open protocol developed by different universities amongst others ETH and EPFL from Switzerland, KU Leuven from Belgium, Tu Delft from the Netherlands.

This comic shows a simple explanation of how it works.

Comic describing the DP-3T protocol

Technically speaking, every day a new random seed (based on the seed of the day before) is created on every user’s phone, and this daily seed is saved on the phone for 14 days. From this seed are derived ephemeral identifiers (EphIDs). These EphIDs change several times an hour.

EphIDs are exchanged with other users of the tracking app by Bluetooth Low Energy (BLE) and every phone saves the EphIDs he received locally on the phone, together with the date and the attenuation of the signal, which can be used to estimate the distance.

When a user is tested positive for COVID-19, this user can, with the help of authorized health personal, upload the seed of the first day he was contagious, to a central server. All previous daily seeds are deleted from the infected user’s phone, and a completely new random daily seed is created, so that he does not become trackable in the future.

All other app users regularly download a list of all daily seeds of all contagious users from the central server and they can derive all EphIDs from them. The app compares all these EphIDs with the list of stored EphIDs which they met recently. Based on the amount of matching EphIDs the app can calculate how long the two have seen each other and based on the stored attenuation it can estimate the distance. If they were longer than a certain time within a certain distance, a warning will be given to the user that they were exposed to a contagious user, with instructions on what to do.

More details can be found in the DP-3T white paper.

Apple/Google Exposure Notifications API

The Google/Apple Exposure Notifications API (sometimes abbreviated as GAEN) is an API created from a joint effort by Google and Apple and enables the creation of decentralized contact tracing apps. This API, which is based on the principles of the DP-3T protocol described above, can only be used by apps approved by Google and Apple (only one per country, and created by official healthcare instances). Only decentralized contact tracing apps which do not collect any location information can get approved.

Apple by default does not allow background apps to use Bluetooth, except for approved contact tracing apps using this API. This means that on Apple iPhone, this API is the only way to create a reliable contact tracing app. Apps which don’t use this API, such as the StopCovid France app, have to apply work-arounds to keep the app waking up in the background, making them potentially less reliable and draining the battery more.

The DP-3T framework has since been modified to make use of the Exposure Notifications API.

Some of the apps currently available using the Google/Apple Exposure Notifications API are SwissCovid (Switzerland), Immuni (Italy), Corona-Warn-App (Germany).

The source code of the implementation of the framework for Android and iOS of the API were published the second half of July 2020.

Frequently Asked Questions – Debunking some myths

These apps appear to be the subject of deliberate fake news campaigns or at least emotional reactions resulting from a lack of understanding of how they work. Here I will try to address some questions.

Will these apps violate my privacy? Will the authorities know who I meet and where I am, what I do?

The applications based on the Google Apple Exposure Notification API do not know any personal information about the users: they don’t know your name, your phone number, where you live, or any other personal data. They also do not collect location data, so they don’t know where you are.

The only thing these apps do, is exchanging anonymous codes with other people in your neighbourhood. These codes change multiple times a day, making it impossible to keep tracking you.

The exchanged codes are only stored on your own phone and not in a central database. So there is no way for the authorities to know how many people and who you met.

Contact tracing apps usually apply even more extensive kinds of measures to protect security and privacy: for example dummy uploads are done in order to prevent network traffic analysis revealing a positive test, CA or certificate pinning to prevent MITM attacks, etc…

This is not a mass surveillance tool or Big Brother, as some try to let you believe.

How can I be sure that the app really works as promised and really does not collect and send private information?

These apps are usually open source, which means you can check the code to see how they work and what they do exactly. Even if you personally don’t have the knowledge to check the code, rest assured that there are enough experts taking a look at this, and will shout loudly when something is wrong. It has to be said: the only ones shouting loudly about these apps are politicians and activists who clearly have never looked at the source code, nor at the documentation. For example code reviews of Coronalert and Immuni have found these apps do live up to their privacy claims.

Here are some links to the source code of the different apps and their documentation:

On the issue tracker of these apps you can report problems and ask questions.

Also the source code of the Exposure Notifications framework, used by these apps, is available:

Why should I trust Google and Apple, who have a bad track record in privacy?

Actually Google and Apple don’t even need this API to track you. If you are running a phone running iOS or Android with Google Play Services, you actually already have much larger privacy problems than these decentralized, open source contact tracing apps. The same if you are using any of Facebook, Twitter, Instagram, TikTok, NetFlix, Spotify, FaceApp, Tinder. These do know your name, your location, your interests, your friends, and this without this API. Decentralized contact tracing apps, do know much less than any of these apps. This picture compares the different permissions SwissCovid, Facebook and Whatsapp can request.

That being said, there is now a way to run these contact tracing apps without using any Google services on your phone. The microg project now includes its own completely open source implementation of the Exposure Notification API. It can be installed on an Android distribution like LineageOS. It is confirmed that SwissCovid and Immuni work with microg’s implementatoin of the API, probably other apps do too. This way you can run these applications without having to rely on any of Google’s or Apple’s proprietary binaries.

Why does this app require Location setting to be enabled on my Android phone if no location information is collected?

To scan for nearby Bluetooth devices on Android the Location setting needs to be switched on because Bluetooth scanning can in theory be used to determine your location. For example this is used by navigation apps to determine your location in underground tunnels. In reality, apps making use of the GAEN API are not allowed to request your location. It can be verified in the source code of the app that at no time it determines your location. In Settings > Location > App permission you can still disable location access to apps. In Android 11, which came out in September 2020, it is noe required any more to have Location enabled on your device in order to use contact tracing apps based on the Exposure Notification API.

Will this app give me a warning every time an infected person passes nearby, resulting in many false positives?

The apps will only give warnings when certain conditions, usually defined by the government based on epidemiological data, are satisfied. For example, the Italian Immuni app will give a warning when someone is standing within a distance for 2 metres for at least 15 minutes. The SwissCovid app requires a 15 minute contact within 1,5 metre distance. Coronalert will show you also low-risk exposures in the app, however only in case of a high-risk exposure (at least 15 minutes within 1,5 – 2 m of distance) will result in a red screen and an explicit exposure notification. Only in this case a test and quarantine is recommended.

The distance is estimated from the attenuation of the signal. Unfortunately, attenuation will depend on lots of parameters, such as the the phone model being used and the direction in which it is hold, etc. Google adds a per device correction value to the attenuation so that values should be similar between different devices. The thresholds being used are based on experiments in different environments and can be modified in the future in order to lower false positives and negatives. Immuni for example uses an attenuation threshold of 73 dBm.

So no, contact tracing apps are not going to give you a warning when anyone who shortly passed nearby, is tested positive. Only when reasonable thresholds are exceeded, you will get a warning. Nevertheless, false positive and false negatives are possible. Authorities also realize this, and view the tracing app as a support tool for tracing, but not as a complete replacement for manual contact tracing. A contact tracing app also does not replace a diagnostic test.

Are these apps useful if not everyone or at least a large part of the population downloads them?

Contact tracing apps are certainly useful, even if only a part of the population uses them.

A highly quoted article from Oxford University states that if 60% of the population installs the contact tracing app, this can completely stop the epidemic. However what is often not quoted is the next part of the phrase: “even with lower numbers of app users, we still estimate a reduction in the number of coronavirus cases and deaths.” They estimate that that one infection will be averted for every one to two users.

So even much lower numbers than 60% are useful to help flattening or crushing the curve, saving lives.

Will this drain the battery of my phone?

By using Bluetooth Low Energy, battery consumption should be limited. Bluetooth Low Energy was created specifically for low energy consumption and is also being used to connect to smartwatches and wireless headphones. Battery consumption should be less than 5% in the worst case, if you otherwise did have Bluetooth completely disabled.

Do I need to install another app when I go abroad?

With support of the European Union, a gateway service has been built that allows the exchange of keys of infected persons between European countries. The 19th of October 2020 the Italian (Immuni), German (Corona-Warn-App) and the Irish app (StopCOVID Tracker) started using this. It is planned that other decentralized contact tracing apps of the European Union will connect to this this gateway too, for example the Belgian Coronalert will add support in November.

However note that keys can never be exchanged with the StopCovid France app because this one uses a centralized system instead of the decentralized DP-3T.

What do experts say about these apps?

First it’s important to repeat that DP-3T, and hence the Google/Apple Exposure Notifications framework based on it, were designed by academics from universities in different countries. Prof. Bart Preneel (KU Leuven), cryptographer, who contributed to the DP-3T framework, says that “for once, Google and Apple are on the right side of privacy“.

The British Information Commissioner’s Office (the national data protection authority) “believes the CTF (Google/Apple’s contact tracing framework) is aligned with the principles of data protection by design and by default, including design principles around data minimisation and security.”

In a report from prof. Douglas Leith (Trinity College Dublin), analysis of network traffic of contact tracing apps was done. He concludes: “We find that the health authority client apps are generally well behaved from a privacy point of view, although the privacy of the Irish, the Polish and Latvian apps could be improved.” They criticize the closed source nature of the Google/Apple Exposure Notifications framework though and the fact that Google Play Services sends private data to Google (something which happens on any Android phone having Google Play Services installed, irrespective of the presence and usage of this framework). Update 23 July 2020: the source code of the framework itself is now available.

The biggest criticism of the framework appears to come from prof. Serge Vaudenay, cryptographer of EPFL. He complains about the closed source nature of the GAEN, and the fact that some attacks are possible. There is an answer by the DP3T team to one of his papers. Update 23 July 2020: the source code of the GAEN framework itself is now available.

Conclusion

Forget all conspiracy theories and emotional objections by privacy activists who never looked at how these apps work: open source decentralized contact tracing apps making use of the Google/Apple Exposure Notification API are not Big Brother, no mass surveillance instrument. The protocol has been developed by academics specialized in security and privacy in IT and the source code of the apps can be verified by anyone. Extensive documentation describes the working of the apps and what is being done to protect the privacy of the users. By using anonymous ephemeral IDs and not collecting any location information, these contact tracing apps know less from you than the average social network app or your phone’s OS itself, so if you are worried about privacy, you have more important things to look at.

Contact tracing apps can be very useful in combating this epidemic, also if only a small part of the population is using them. For me it’s simply a matter of responsibility installing these apps: to protect others, to protect our society and economy and in the end to get protected myself by others using the app.

Further information

History of this article

Update 23 July 2020: Added links to the source of Google and Apple Exposure Notifications framework – Added info about Belgian contact tracing app in development – Added link to picture comparing permissions requested by SwissCovid, Facebook and Whatsapp

Update 6 September 2020: Added question about Location requirement on Android phones

Update 19 September 2020: Added link to source code of Belgian Coronalert app – Added info about an Expsore Notifications API implementation in microg, enabling you to run these apps without Google services

Update 4 October: add information about EU gateway service

Update 19 October: EU federation gateway service in use by 3 apps

Teufel Connector review

Already for some time, I was thinking of buying a music streamer to connect to my hifi set in order to listen to my audio cd collection I ripped to my computer (using whipper, and tagged with Musicbrainz Picard). Because I have many mix albums, gapless playback support is important. I would prefer a very broad codec support, at least including FLAC and Ogg Vorbis but by preference also Opus. Because the proprietary applications by the music streamer vendors don’t always get very good reviews, I would like to be able to control them with a third party app like BubbleUPNP, still with gapless playback. And of course I don’t want to break the bank too much.

I recently thought I found the perfect device for that: the Teufel Connector. Because of a sale I could buy this streamer for less than 140 €.

The Teufel Connector is a little box, unfortunately not being of the same size as a standard hifi component. It does not have a remote control and it also does not have a display, so the only way to control it is via the Raumfeld app on your smartphone or tablet. You can connect it via Ethernet or wifi. It does have analog and digital optical outputs, and features also analog inputs, which allows it to stream any other audio device to other multi-room Raumfeld devices in your house.

Setup

The Raumfeld app guides you through the setup process. In contrast to some information I read on the Internet, I did not have to connect my device with an Ethernet cable to set it up: you can immediately set it up to connect to your wifi network via your smartphone. I had some trouble that when I entered the wrong wifi password, not only did I have to restart the device in order to restart the startup procedure, I also had to delete all data of the Raumfeld app in order to get back to the setup screen. Maybe there is another way, but apparently this was not very intuitive. In the end I managed to set it up and the device became available.

The Raumfeld app

Playback from UPNP/DLNA server

Adding a remote UPNP/DLNA server to the Raumfeld app can be done through the app’s settings. It should list all UPNP servers, so you just have to pick it from a list. All music will then appear in the My Music part in the application.

It properly shows the album art, even if they were not saved in the music files or directory. However a serious problem shows up: it does not properly show albums containing tracks by different artists, such as compilations. Even though the Album Artist tag is correctly set (e.g. to Various Artists for compilations) Raumfeld will not create one album which contains all tracks. Instead it will create a different album with the same name for every single different artist on the disc. Obviously this is a huge problem, because it makes it impossible to play back entire compilation albums in one go. There is a tab Directory Structure in the app, but when trying to browse the directory structure of the server, it states that browsing is not available for remote music servers. So this is not an alternative either to browse albums correctly.

Playback from SMB server

So if Raumfeld does not show albums correctly when accessing them via UPNP, does it do any better when accessing them through SMB?

Adding an SMB share happens again through the app’s settings. The app never mentions SMB but only uses the term “network sources”, so this was a bit confusing. You have to enter hostname or IP address, username and password, and then you will be able to select the share you want to use. Adding your library via SMB takesa much longer because now all files have to be indexed by the Connector itself, while with UPNP this is done server side.

The good news is that this time, the problem with the compilation albums does not occur. What I don’t like however, is that albums containing multiple disks are still shown as multiple albums, one for each disk. The first disk just has the album name, the second one the album name followed by [disc 2], and so on. This way, playing a complete album requires a manual action again to switch discs, which is a pity. I would have preferred them to be shown as one album, with a division between the different discs in the track listing. Gapless playback works fine.

Several times while playing it would all of a sudden randomly switch to another track. This seems to happen especially while it’s scanning the music on the SMB source. This is very annoying and a serious bug which needs to be fixed. When it has finished scanning, this problem does not occur any more. In the app, you can set it to scan automatically every day, or to scan only when you manually ask it do so. Anyway, scanning your library is needed when you added new music files, so this is a huge problem if your library is not static. I contacted support for this problem, and they even do not consider this to be a bug. They blame the wifi network, and tell me that it probably would not happen if I would play MP3 files instead of FLAC. This seems complete nonsense to me: while scanning the music files, there is about 120 KB/s traffic between server and Connector, and when simultaneously playing a FLAC file it would jump occasionally to less than 2 MB/s. With the server connected by UTP to the router, and the Connector being less than 5 meters away from the router in the same room, bandwidth problems cannot explain this at all.

Playback from a local USB device

The Connector has a USB port to which you can connect an external disk. The Connector automatically indexes all music files and adds them to the library. I have not extensively tested this feature.

Playback of Internet streams

Raumfeld supports playback of a number of different Internet sources, such as Spotify, TuneIn, Soundcloud, Tidal and Napster. Maybe this is not the most complete offering of streaming services (for example Google Play Music, Amazon Music and Deezer are not there), but these other services can usually by accessed by means of Chromecast. More on that later.

TuneIn

For radio streams, TuneIn is used. You can check if your favourite station is included on the TuneIn website. If it’s not available, you can always add a custom stream in the Raumfeld app, but currently you need the beta version for that.

There is no way to link Raumfeld with your TuneIn account, so it is not possible to import your TuneIn Favourites in case you used TuneIn before.

Unfortunately many radio streams use a bitrate which is a bit too low for perfect quality. Of course this is not Teufel’s nor TuneIn’s fault, but keep this in mind in case you consider replacing your FM or DAB+ tuner by a network streamer.

Spotify

The Connector supports Spotify Connect, which means you can play Spotify music on your Connector directly from the Spotify app if you have a Spotify Premium subscription. I don’ t have such a subscription at the moment so I did not test it.

Soundcloud

To use Soundcloud, you need to log in with a Soundcloud account. Then all the artists you follow, tracks you liked, etc. will appear in the Raumfeld app. For an unknown reason to me, I could not find some tracks available on the website, such as the Purified radio show.

Unfortunately it is not possible to like tracks and follow artists on Soundcloud via the Raumfeld app, so you still need to do this via the website.

Use of the Raumfeld app

The Raumfeld app contains the basic features to get your music playing, but they should definitely take a look at the Spotify app to see how things can be made much more user friendly.

The Raumfeld app has a permanent notification in your notification list, where you can see what is playing, pause playback, switch to the previous and next song, and change the output volume (at least if you are using the analog output to your amplifier). There is also a widget available if you prefer that.

Playing just random tracks from your library, but it’s not as easy as it could be. Unlike Spotify, there is no big green Shuffle button in the All tracks tab page of the app. Instead you have to start playback by choosing a random song yourself and start playback, and enable the Shuffle option in the now playing window. Actually, after a while I discovered that there is actually an easy option hidden in the Playlist section, where there is a pre-defined playlist “My Music Shuffle”. This could be easier to find.

In the Now Playing window, there there is no option to go immediately to the album of the playing track, or to the list of all tracks of that artist. This is a handy feature that can be found in Spotify and other music players.

There is no way to properly close the Raumfeld app, except for going to Android’s settings and killing the app there. I have noticed several times when going away from home, and then connecting to another wifi network, the permanent notification would still be there as if I can start playback immediately. After some time eventually, the notification will say that the player is not available, giving you the options to close the app by pressing the X in the notification. I think there really should be a way to manually quit the application at any time.

While it’s possible to add different network sources to your music library, they all get mixed up in one big library, while I would prefer them to be in two different libraries. For example, I have two different SMB shares, one for classical music, and another one for pop music. When I want to play music, I want to have the possibility of seeing only the albums from the classical music library or only albums of the pop music library. This could be done by creating subitems for every single network sources under My Music in the menu. Choosing My Music would bring you to a combined library, while tapping one of the subitems would only show the contents of that network source. Unfortunately, the app does not make that possible, and you end up with all network sources mixed up.

The Dutch translation of the Raumfeld app needs some work. For example there is a button “Verwijder bron” (= Remove source) in the sources settings. When choosing this option it asks for confirmation: “Verplaats bron?” which actually means “Move source”. When clicking on the Delete button in a playlist, the possible answers to the question whether you are sure are “Geen” (= None) and “Ja” (= Yes). And in the Playlist section, the wrong word Schuffles is used. Even if not really a great translation, at least Shuffles would more acceptable. I noticed other errors too, so they really need to do some work proofreading the Dutch translation.

Playback via BubbleUPNP

I had a disappointing experience using the Raumfeld app, when playing either from my UPNP server or my SMB server. What if I use BubbleUPNP instead?

BubbleUPNP sees the Connector in 3 different ways: one as a single Connector UPNP render, one as meta-device named after the room (this would contain all Teufel UPNP devices you have added to that room), and once as a Chromecast device.

When playing music to the Connector, the playback time is not updated in BubbleUPNP. You cannot go forward or backwards within the track and get the error: “Seek mode not support (code: 710)”. When the song is finished and it continues with the next song, BubbleUPNP does not even notice that it went to the next song. So this is not usable.

When using the virtual room device as a renderer, plaback time is updated and seeking does work. However, gapless playback is not supported at all. This is also the case when letting BubbleUPNP stream to the Chromecast device.

All in all, the Connector does not have flawless UPNP support making it BubbleUPNP not a usable alternative to the Raumfeld app.

Chromecast support

Every application which supports Google Chromecast, and many music applications in Android do, can cast their stream to the Connector. It’s as easy as pressing the cast button in the application, and then selecting your Connector. It works simple and good and allows you to listen to streaming services which are not natively supported by the Raumfeld app.

Audio quality

Hifi magazines usually spend the most time writing about this subject when reviewing audio hardware, but I have the feeling that this is purely psychological and that there is rarely any audible difference between different audio source hardware. I can only say that there is nothing wrong with the audio quality of this device, and I don’t believe a device which costs 5 or 10 times as much can sound any better.

Of course all depends of the quality of your source material. I am using FLAC files directly ripped from CD, so there is no quality loss there. When listening to lower bitrate Internet streams (and unfortunately many of them still use older codecs such as MP3 in combination with a not high enough bitrate), you will of course clearly hear that it’s far from CD quality, but that is not something your hardware can fix.

The Connector should support playback of hi-res audio files up to 24 bit 192 Khz, but I have not tested this.

Support

On the Dutch website, there is contact page mentioning e-mail and a contact form, however no e-mail address nor contact form for technical support questions can be found there. On the repair and returns page there is the address service@teufelaudio.nl. This should be easier to find.

Support has been useless to me. I contacted them regarding the problem with the compilation albums on UPNP but seemed clueless, and they blamed the problems on the automatic switching of tracks on my wifi network, denying any bug there.

Conclusion

The Teufel Connector is a versatile machine supporting many codecs (including Opus and high-res music files) and gapless playback. Thanks to the Chromecast support, you can stream many online services to the device, even though the Raumfeld app itself only supports a limited selection of sources. The price is low, as is power consumption. So in theory this should be a great device, at least if you can live without a dedicated remote control, display and control buttons on the device itself.

Unfortunately the Connector is completely let down by the buggy firmware and Raumfeld app. UPNP was totally useless to me because it does not correctly show albums containing tracks of different artists. SMB on the other hand, requires a lengthy scanning process, during which it is impossible to listen to music from your library because it randomly switches tracks the whole time. BubbleUPNP is not a usable alternative for the Connector, because the Connector’s implementation as a UPNP media renderer also appears to be incomplete and buggy.

Several times during usage I encountered hangs in the Raumfeld app, or of the Connector device itself, requiring to disconnect the power to force a hard reset. Whether I used the stable version of the app or the beta version, did not make any difference. I did not try the beta version of the firmware.

All these problems could still be fixable by firmware and app updates. But is it realistic that they still will get fixed, knowing that this device is already on the market for years, and is being superseded by the Teufel Streamer now? The Raumfeld app only gets a score of 3.0 in the Android Play Store and there are many complaints, also in combination with other Teufel Raumfeld devices.

In conclusion I cannot recommend this device if you want to use it mainly to play your local music library. If you want to use it only to listen to online streams, than you could consider it, but otherwise, look further.

It’s disappointing that in 2019 finding a good streamer is still not easy. Much more important than the hardware, is the firmware and software. If you have to choose which music streamer to buy, I strongly recommend reading the app reviews on the Play Store instead of reviews of so-called hifi and multimedia magazines. Looking at the app reviews, then Sonos with a score of 4.0 seems to be the best one, followed by Heos from Denon and Marantz (3.6). Cambridge Audio’s StreamMagic (2.9, however only 7 reviews now as it is brand new), Onkyo’s Controller (2.9), Pioneer’s Remote Control (3.0), which appears to be the same as Onkyo’s, Yamaha’s Musiccast (3.0) don’t seem to be any better than Raumfeld unfortunately.

What’s your experience with this or with other streamers, such as the Denon DNP-800NE or Marantz NA6006, the Yamaha NP-S303, or anything else? Do they support gapless playback, also when using BubbleUPNP? How stable are they and is the app user friendly? Can you create multiple, separate libraries in it?