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Corona Contact Tracing Germany
The app has shut down
The Corona-Warn-App has ramped down at the end of April 2023. With the shutdown of crucial server-side services like sharing keys to warn others, CCTG is, for the most part, no longer functional. We have no intention of operating our own server infrastructure for multiple reasons (the most important one being that CCTG has a comparatively small userbase, making it very unlikely to be able to warn anyone).
Talk to us
- Join the matrix room: #cctg:bubu1.eu, also bridged to XMPP: xmpp:email@example.com?join
- Follow us on Mastodon: @CCTG@social.tchncs.de
Get The App
Our F-Droid repository contains beta versions and is updated with new releases immediately. After a few days, stable releases will also be available in the standard f-droid.org repo. You can also verify the builds yourself, see Reproducible Builds.
Note: This project contains nested submodules. Please execute
git submodule update --init --recursive after cloning the repository when building outside of the F-Droid build setup.
Make sure to build
Corona-Warn-App in Android Studio and not the microG app (GmsCore.play-services-core). Otherwise you'll get lots of strange errors.
This is a fork of CWA without proprietary dependencies. While the German Corona Warn App itself is Free Software, it depends on Google's proprietary Exposure Notification Framework. This fork instead uses the drop-in compatible microg implementation.
While we've had many reports of users successfully running the app on various Android versions it's by far not as well tested as the official Corona-Warn-App. Use at your own risk! It should work on any Android 5+ device regardless of installed play-services or microg versions.
If microG is already installed on your system, it will make use of its Exposure Notifications implementation. Otherwise, it will use the bundled implementation. It will never connect to the Google Play services Exposure Notification System. You can find out which implementation is used by checking the status at the bottom of the App Information screen.
There's currently no translation system in place as most translation are taken directly from CWA. There's some small bits left to translate/fix for Romanian and Turkish. Please contact us!
The FAQ is also available in German.
I'm encountering Error 39507 when enabling risk notifications.
This version is not available on f-droid.org yet because reproducible builds are not working yet (#288).
Why can't I Warn Others with a self-test in CCTG?
SafteyNet attestation is required to certify that the original, unmodified CWA app is used to Warn Others after positive self tests or after positive test results not provided to the app. This means that the feature is unavailable to thid-party apps.
My Encounters page shows no IDs even though Exposure Logging is enabled. What can I do?
This usually means that the scanner service is getting stopped in the background.
- Activate "Prioritized Background Activity" in the app's settings menu. This is most important.
- If you are using external microG, verify that all necessary permissions are granted in the Self-Check inside the microG Settings app, as well as that "Battery optimizations ignored" is checked there. Activate missing permissions. This is equally important.
- Whether you are using external microG is indicated at the bottom of the App Information screen.
- Disable any other battery-saving services that your Android vendor is providing to you for CCTG. There is some information and instructions available on this website: https://dontkillmyapp.com/?app=Corona%20Tracing
- Avoid to enable your phone's battery saving mode when possible. It's likely that this will make the scanning functionality less reliable.
The scanner service should restart whenever you manually disable Exposure Logging and enable it again.
- Restart the scanner service.
If you notice that scanning stops again eventually and you would like to contact us regarding this, it's best if you include details about your operating system and device vendor, as well as an indication that you followed the instructions above.
Why does the Encounters graph card not display a scale?
Some people do not know that IDs are rotated regularly, and are therefore surprised about the amount of IDs that their device collects.
Because the card is not a good place to provide further details, we have decided not to include a scale on this chart.
How does the ID matrix graph work?
Every device participating in contact tracing constantly emits random IDs, which your device collects and displays in the graph. Since IDs are rotated every 10 minutes, one single device in your proximity can cause up to 6 collected IDs per hour.
At home, you may also collect IDs from your neighbors depending on your and their Bluetooth antenna as well as isolating properties of the walls that separate you.
The approximate distance to an encounter is not displayed, since this information can only be calculated once additional information is revealed by an infected person in the process of Warning Others. The same applies to the knowledge which IDs belongs to the same device. Both pieces of information are used to make the risk calculation more precise.
Are QR codes for events and locations compatible with other apps?
CWA has worked out a standard, according to which compatible QR codes should be generated.
Since November 9, 2021, the Corona-Warn-App as well as CCTG are able to scan luca QR codes created after May 24, 2021.
No additional update is required to take advantage of this, as the Check-in functionality is expanded through a server-side configuration change.
For more information, please take a look at the related blog post from the Corona-Warn-App team.
Can I use CCTG outside of Germany? What if I don't live there?
Yes! You can be warned about Bluetooth encounters in each of the countries that are included in this list: https://www.coronawarn.app/en/faq/#interoperability_countries
You can not receive test results from these countries. In case you are infected and confirmed this through a PCR test, however, you may call the TAN hotline to receive a code that allows you to warn others.
The Vaccination Certificate follows an EU-wide standard and thus supports QR codes from all member states as well as Switzerland.
Check-In functionality is not designed to work internationally at the moment, as check-ins are not shared with contact tracing applications of other countries or those apps don't provide such functionality at all. However, theoretically, the functionality is available without limitations.
What is the difference to CWA?
The official Corona-Warn-App build contains a proprietary component to interact with the Exposure Notifications API, even if microg is installed instead of Google Play Services.
Corona Contact Tracing Germany replaces this proprietary component with a different library provided by the microg project, meaning that it is built as fully free software (in contrast to Corona-Warn-App).
Our app also ships with the relevant components to also function as a standalone app if microg is not installed.
Additionally, we have the following "exclusive" features, though we are always willing to contribute our improvements back to CWA:
- Incompatibility warning card (cwa-app-android/#2481) – included from CWA 2.2 onwards
- Battery optimizations warning card (cwa-app-android/#2682)
- Android 5 support (cwa-app-android/#1799, cwa-app-android/#2026, cwa-app-android/#2700, cwa-app-android/#2844, cwa-app-android/#2955)
- Encounters card on the Status screen
- with a link to external microG if external microG is used
- with an ID count on day 1 or if no IDs have been collected for the past 5 days
- with an ID bar chart otherwise
- Translucent status bar (cwa-app-android/#2483)
- Lifted rotation lock (cwa-app-android/#5355)
- Lifted backup block
- Ability to export collected IDs, for example for use with the Companion app (through microG)
Due to an upstream decision, CWA's data donation (privacy preserving analytics, PPA) and survey features are not available in CCTG, as they require Google SafteyNet attestation. (cwa-wishlist/#356)
CWA shows some exposures but CCTG doesn't, or the other way round.
Both apps are periodically scanning for encounters in the background, but not exactly at the same time. Therefore, both apps can collect slightly different data and reach different conclusions about your risk status.
microG/CWA Companion shows some exposures but the app says there were none.
Starting with version 1.9.1 this is expected, see the official blog post:
In simplified terms: Under Exposure Notification Version 2.0, the operating system also logs encounters with a risk lower than "low risk" (green). However, since these encounters are not relevant from the current epidemiological perspective, the Corona-Warn-App filters them out.
How does the app manage to stay alive in the background? Didn't everyone say that's impossible?
This may be correct for iOS; for Android, the platform is supposed to allow you to grant exceptions from battery optimization procedures.
Do I need microG/signature spoofing for this?
No, this app bundles a standalone version of the microG implementation that will get used when there's no microG system installation found.
Why does the app need location permission?
The app doesn't access GPS or Network location but Android considers bluetooth scanning a form of location access (because you could derive location information from the info you could get there), see here for details: https://stackoverflow.com/a/44291991/1634837. CCTG doesn't do any location tracking though.
On Android 11 Google allowed the play services ENF implementation to do Bluetooth scanning in the background without special location permission. CCTG isn't allowlisted of course and thus needs to still ask for full location permission in Android 11.
On Android 11, it is necessary to explicitly set location access to Always enabled through the settings menu in order to enable Exposure logging. This video demonstrates how to do that.
On Android 12, it is additionally required to grant the Nearby Devices permission. However, from version 18.104.22.168 onwards, the application can be used without location permissions.
When will updates be released? When is the app coming to F-Droid?
Shortly after an update to CWA is released, we will release a new version of CCTG. New versions are immediately available on our repo.
In the first stage of our "transparent staged rollout", the app is not marked as "suggested" yet, meaning that your F-Droid client won't recommend it as an update, though you can install it manually. We do this to be informed about crashes and other issues by users who knowingly choose to try out a version that might not be stable yet.
Once we feel that all issues are sorted out, we will mark the most recent version as "suggested", causing users of our repository to receive the update immediately (once their F-Droid client refreshes the repository).
After some time, the latest version also appears in the official F-Droid repository, though as usual for F-Droid, this can take a while. Therefore, please be patient. F-Droid will serve exactly the APK that we also have in our repo, because our app builds reproducibly.
You might want to follow our mastodon account, where we will announce new versions.
How to migrate from CWA
Since all epidemiologically relevant data automatically gets deleted after two weeks, you can use both CCTG and CWA at the same time for two weeks and uninstall CWA afterwards. Disable Exposure Logging in CWA before installing CCTG and begin using CCTG to check in to events and locations.
Migrate each certificate that is stored in the Certificates tab in CWA by scanning their QR code in CCTG.
If you have registered CWA as a default application for event or rapid test URLs, unregister CWA through the system settings so that these links can be opened with CCTG in the future.
In case of an infection
In case you are tested positive and would like to warn others, call the TAN hotline and ask for an additional TAN. State that you have been using two separate installations that store different data.
Interpreting risk warnings
If you are running CWA with microG, CWA and CCTG share the random Bluetooth IDs and will both use those that the other app had collected as a basis for their risk calculation. The indicator that shows how many days ago the respective app was installed is purely cosmetic and not relevant for risk calculation.
If you are running CWA with Google's Exposure Notification System, this is not the case and each app is only able to use the dataset that it has collected itself.
In none of these situations is any of the apps able to use the events and locations of the other app for risk calculation. Each app only uses the items that are shown in their respective Check In tab.
CCTG says I need to update microG but this isn't working
Some ROMs come with a version of microG that is signed with a different key from the one the microG project distributes, in this case you need to wait for your ROM to update their built-in microG version before you can use the new CCTG version.
CCTG version 1.9.1.X needs microG at least version 0.215 to work. The previous version (1.7.1) needed at least version 0.2.14 but this wasn't enforced.
If you already updated you can try following this comment to see how to downgrade to 1.7.1 again. You can also uninstall CCTG and reinstall the older version. Your exposure data (but not pending or received test results) will be kept intact inside the microG installation. The app will start counting from day 0 again but this makes no functional difference.
How do I access the microG exposure notification settings in the standalone app?
Since version 22.214.171.124, an Encounters card is available on the app's Status tab. Touch it to open the encounters graph contained in microG.
Previous versions up until 126.96.36.199 instead included a bottom tab that displayed the same view.
If you however want to access the other microG Exposure Notification settings screens, you can still follow these steps:
Open the exposure logging settings by clicking on the "Exposure logging active" (or "Exposure logging stopped", etc.) section above your risk status on the main screen. From there, select "Open advanced settings". It'll magically take to to the correct (integrated or external) microG EN settings page. If you're still unsure what to do, the video attached to this post may help you.
Alternatively, go to App Information (via the three-dot/kebab menu) and then tap on the status text at the very bottom. This will bring you to the same screen. This used to be the only option in earlier versions.
There's a card on my home screen telling me that my device is only partially compatible. What does this mean?
This FAQ entry has been moved upstream to CWA.
I have seen that others have a bar chart with their encounters on the home page. I don't see this?
This widget is only displayed if you are using the internal microG instance. For technical reasons, the chart cannot be displayed or included directly if you are using an external microg version that is bundled with your operating system/CustomROM. Instead, you will see a button that you can press which will take you to the same screen with more information on this topic.
If you have run the exposure logging for less than one or two days, no bar chart is shown either.
Does CCTG run on Sailfish devices?
Yes, BUT with one important caveat: Apps running via the Sailfish Android compatibility layer can't access the devices Bluetooth functionality so the core contact tracing functionality won't work. All other functionality like check-ins, contact diary, receiving test results and saving vaccination certificates is available though.
We've also heard people successfully use the Sailfish native app Contrac for the contact tracing functionality.
Official Corona-Warn-App FAQ
The FAQ for the Corona-Warn-App partially also apply to CCTG.
- DE: https://www.bundesregierung.de/corona-warn-app-faq
- EN: https://www.bundesregierung.de/corona-warn-app-faq-englisch
See docs/rebuilding.md on how to reproduce the official builds.