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# Corona-Warn-App
<p align="center">
<a href="https://www.coronawarn.app/en/"><img src="https://raw.githubusercontent.com/corona-warn-app/cwa-documentation/master/images/CWA_title.png" width="400"></a>
</p>
<hr />
<p align="center">
<a href="#about-this-project">About this Project</a>
<a href="#who-we-are">Who We Are</a>
<a href="#credits">Credits</a>
<a href="#data-privacy">Data Privacy</a>
<a href="#code-of-conduct">Code of Conduct</a>
<a href="#working-language">Working Language</a>
<a href="#our-documentation">Our Documentation</a>
<a href="#licensing">Licensing</a>
<a href="#how-to-contribute">How to Contribute</a>
<a href="https://www.coronawarn.app/en/">Web Site</a>
</p>
<hr />
NOTE: This README is also available [in German](translations/README.de.md). Thank you for understanding that the German version might not always be up-to-date with the English one.
HINWEIS: Diese README ist ebenfalls [auf Deutsch](translations/README.de.md) verfügbar. Bitte haben Sie Verständnis, dass die deutsche Version nicht immer auf dem gleichen Stand wie die englische Version ist.
## About this Project
We are developing the official COVID-19 exposure notification app for Germany, called "Corona-Warn-App". This project has the goal to develop an app based on technology with a decentralized approach - heavily inspired by the [DP-3T](https://github.com/DP-3T/documents) (Decentralized Privacy-Preserving Proximity Tracing) and [TCN](https://tcn-coalition.org/) protocols and based on the [Privacy-Preserving Contact Tracing specifications](https://www.apple.com/covid19/contacttracing/) by Apple and Google. Like DP-3T and the TCN Protocol, the apps and backend infrastructure will be entirely open source - licensed under the [Apache 2.0 license](LICENSE)! The apps (for iOS and Android) will collect pseudonymous data from nearby mobile phones using Bluetooth technology. The data will be stored locally on each device preventing access and control over data by authorities or anyone else. We will meet the applicable data protection standards and guarantee a high level of IT security. By doing so, we are addressing people's privacy concerns and thereby aiming to increase the adoption of the app.
We are developing the official COVID-19 exposure notification app for Germany, called "<a href="https://www.coronawarn.app/en/">Corona-Warn-App</a>". This project has the goal to develop an app based on technology with a decentralized approach - heavily inspired by the [DP-3T](https://github.com/DP-3T/documents) (Decentralized Privacy-Preserving Proximity Tracing) and [TCN](https://tcn-coalition.org/) protocols and based on the [Privacy-Preserving Contact Tracing specifications](https://www.apple.com/covid19/contacttracing/) by Apple and Google. Like DP-3T and the TCN Protocol, the apps and backend infrastructure will be entirely open source - licensed under the [Apache 2.0 license](LICENSE)! The apps (for iOS and Android) will collect pseudonymous data from nearby mobile phones using Bluetooth technology. The data will be stored locally on each device preventing access and control over data by authorities or anyone else. We will meet the applicable data protection standards and guarantee a high level of IT security. By doing so, we are addressing people's privacy concerns and thereby aiming to increase the adoption of the app.
## Who We Are

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@ -33,20 +33,24 @@ To reduce the spread of [COVID-19](https://www.ecdc.europa.eu/en/covid-19-pandem
![Figure 1: High-level architecture overview](images/solution_architecture/figure_1.svg "Figure 1: High-level architecture overview")
With the Corona-Warn-App (see [scoping document](https://github.com/corona-warn-app/cwa-documentation/blob/master/scoping_document.md )), shown centrally in *Figure 1*, individuals are enabled to trace their personal exposure risk through the means of their mobile phones. The application makes use of a new API made available by Apple and Google, called [Exposure Notification Framework](https://www.apple.com/covid19/contacttracing). It employs [Bluetooth Low Energy (BLE)](https://en.wikipedia.org/wiki/Bluetooth_Low_Energy) mechanics that let the individual phones act as beacons (constantly broadcasting a temporary identifier (called Rolling Proximity Identifier RPI) to be remembered by), while scanning for identifiers of other phones at the same time (shown on the right side of *Figure 1*).
With the Corona-Warn-App (see [scoping document](https://github.com/corona-warn-app/cwa-documentation/blob/master/scoping_document.md )), shown centrally in *Figure 1*, individuals are enabled to trace their personal exposure risk through the means of their mobile phones. The application makes use of a new framework made available by Apple and Google, called [Exposure Notification Framework](https://www.apple.com/covid19/contacttracing). It employs [Bluetooth Low Energy (BLE)](https://en.wikipedia.org/wiki/Bluetooth_Low_Energy) mechanics that let the individual phones act as beacons (constantly broadcasting a temporary identifier (called Rolling Proximity Identifier RPI) to be remembered by), while scanning for identifiers of other phones at the same time (shown on the right side of *Figure 1*).
Identifiers are ID numbers sent out by the phones. To ensure privacy and prevent tracking of movement patterns of the app user, those broadcasted identifiers are only temporary and change constantly. New identifiers are derived from a Temporary Exposure Key (TEK) that substitutes daily at midnight (UTC) through means of cryptography, which will be explained in more detail in *Figure 10*. When the TEKs are linked to a positive test, they remain technically the same, but are called Diagnosis Keys.
The collected identifiers of other users, as well as the own keys (which can later be used to derive the identifiers) are stored locally on the phone within the secure storage of the framework provided by Apple and Google. This secure storage cannot be accessed directly by the application, but only through the interfaces provided by the Exposure Notification Framework. Some of those interfaces are subjected to [rate limiting](https://developer.apple.com/documentation/exposurenotification/enmanager/3586331-detectexposures), in order to prevent misuse. In case users were tested positively for SARS-CoV-2, they can update their status in the app by providing a verification of their test and select an option to send their recent keys of up to 14 days. Once the keys have been uploaded to the Corona-Warn-App backend server, all keys of positively tested people are aggregated. This list of keys is then made available to all mobile phones with the app installed. Additionally, configuration parameters for the framework are available for download, so that adjustments to the calulation of the risk score can be taken (see the section regarding *Risk Scores*).
Once the keys and the exposure detection configuration have been downloaded, the data is handed over to the Exposure Notification API, which analyzes whether one of the identifiers collected by the phone matches to those of an infected person. Additionally, meta data that has been broadcasted together with the identifiers (e.g. transmit power), can now be decrypted and used. Based on the collected data a risk score for each individual exposure as well as for the overall situation is calculated for every single user within the Exposure Notification framework by Apple and Google. Exposures are defined as an aggregation of all encounters of an individual on a single calendar day (UTC timezone). For privacy reasons it is not possible to track encounters with other individuals across multiple days.
Once the keys and the exposure detection configuration have been downloaded, the data is handed over to the Exposure Notification framework, which analyzes whether one of the identifiers collected by the phone matches to those of an infected person. Additionally, meta data that has been broadcasted together with the identifiers (e.g. transmit power), can now be decrypted and used. Based on the collected data a risk score for each individual exposure as well as for the overall situation is calculated for every single user within the Exposure Notification framework by Apple and Google. Exposures are defined as an aggregation of all encounters with another person on a single calendar day (UTC timezone). For privacy reasons it is not possible to track encounters with other individuals across multiple days.
It is important to notice at this point, that the people that have been exposed to a positively tested person are **not informed by a central instance**, but the risk of an exposure is calculated locally on their phones. The information about the exposure remains on the users phone and is not shared.
The app pursues two objectives: First, supporting individuals in finding out whether they have been exposed to a person that has later been tested positively, and second receiving results of a SARS-CoV-2 test on their phone through an online system. This helps to reduce the period until necessary precautions (e.g. contact reduction and testing) can be taken. In order to prevent misuse, users need to verify that they have been tested positively before being able to upload their keys. Through this integrated approach, the verification needed for the upload of the diagnosis keys does not require any action from the users. They only have to confirm to the app and the Exposure Notification Framework that they are willing to share their diagnosis keys. Manual verification is also possible, if the lab that performed the testing does not support the direct electronic transmission of test results to the users' phone or if users have decided against the electronic transmission of their test results.
The app pursues two objectives: First, supporting individuals in finding out whether they have been exposed to a person that has later been tested positively, and second receiving results of a SARS-CoV-2 test on their phone through an online system. This helps to reduce the period until necessary precautions (e.g. contact reduction and testing) can be taken.
In order to prevent misuse, users need to provide proof that they have been tested positive before being able to upload their keys. Through this integrated approach, the verification needed for the upload of the diagnosis keys does not require any further action from the users.
They only have to confirm to the app and the Exposure Notification Framework that they are willing to share their diagnosis keys. Manual verification is also possible, if the lab that performed the testing does not support the direct electronic transmission of test results to the users' phone or if users have decided against the electronic transmission of their test results.
### Retrieval of lab results and verification process
Reporting positive tests to the app is crucial for others to get informed about a relevant exposure and potential infection. On the other hand, a verification before the uploaded of diagnosis keys is required in order to prevent misuse.
There are two main approaches for this verification: The first option is to use the integrated functionality of the Corona-Warn-App to retrieve the results of a SARS-CoV-2 test. Through this integration, the positive test result is already verified and the diagnosis keys can be uploaded right after users have given their consent. The second option is to receive a human-readable token (e.g. a number or a combination of words) and provide this as verification to the app. This token is called teleTAN.
Reporting positive tests to the app is crucial for others to get informed about a relevant exposure and potential infection. However, a verification before the upload of any diagnosis keys is required in order to prevent misuse.
There are two ways for receiving this verification:
1. Use of the integrated functionality of the Corona-Warn-App to retrieve the results of a SARS-CoV-2 test from a verification server (see Figure 2, Step 4a). Through this integration, the positive test result is already verified and the diagnosis keys can be uploaded right after users have given their consent.
2. Use of a human-readable token (e.g. a number or a combination of words) and provide this as verification to the app. This token is called teleTAN (see Figure 2, Step 4b).
![Figure 2: Interaction flow for verification process](images/solution_architecture/figure_2.svg "Figure 2: Interaction flow for verification process")
@ -62,8 +66,8 @@ The flow for using the app is as follows, referencing the steps from *Figure 2*:
- (3) When the code is scanned, a web service call (REST) is placed against the Verification Server (*Figure 3*, step 2), linking the phone with the data from the QR code through a registration token, which is generated on the server (*Figure 3*, step 3) and stored on the phone (*Figure 3*, step 4).
- **Step 2:** The samples are transported to the lab (together with a “Probenbegleitschein”, which has a machine-readable QR code on it, as well as multiple other barcodes (lab ID, sample IDs).
- **Step 3:** As soon as the test result is available (i.e. the samples have been processed), the software running locally in the lab (lab client) transmits the test result to the Laboratory Information System, together with the GUID from the QR code. The Laboratory Information System hashes the GUID and the test result. It is made available to the Verification Server through a REST interface.
- **Step 4a:** After signing up for notifications in step 1, the users phone regularly check on the Verification Server whether test results are available (polling, figure 3, steps 5-8). This way, no external push servers need to be used. If results are available, the user is informed about the availability of information and only after opening the app, the result is displayed, together with recommandations for further actions (see scoping document for more details).
- In case the test returned a positive result, users are asked to upload their keys to allow others to find out that they were exposed. If the users agree, the app retrieves a short-lived token (TAN) from the Verification Server (see also *Figure 3*, steps 6-8). The TAN is uploaded together with the diagnosis keys of up to the last 14 days to the Corona-Warn-App Server (*Figure 3*, step 12).
- **Step 4a:** After signing up for notifications in step 1, the users phone regularly checks the Verification Server for available test results (polling, figure 3, steps 5-8). This way, no external push servers need to be used. If results are available, the user is informed about the availability of information and only after opening the app, the result is displayed, together with recommandations for further actions (see scoping document for more details).
- In case the test returned a positive result, users are asked to upload their keys to allow others to find out that they were exposed. If the users agree, the app retrieves a short-lived token (TAN) from the Verification Server (see also *Figure 3*, steps 9-11). The TAN is uploaded together with the diagnosis keys of up to the last 14 days to the Corona-Warn-App Server (*Figure 3*, step 12).
- The Corona-Warn-App Server uses the TAN to verify the authenticity (*Figure 3*, steps 13-15) of the submission with the Verification Server.
- The TAN is consumed by the Verification Server and becomes invalid (*Figure 3*, step 14)
- If the Corona-Warn-App Server receives a positive confirmation, the uploaded diagnosis keys are stored in the database (*Figure 3*, step 16).
@ -120,7 +124,7 @@ It is to note that even if a user has not been tested positive, the app randomly
If diagnosis keys need to be uploaded on subsequent days of the submission of a positive test result, also that behavior should be represented within the random (dummy) submissions.
The possibility to identify temporary exposure keys belonging together (i.e. to the same user) is given, as they are posted together resulting in them being in a sequential order in the database. To prevent this, the aggregated files will shuffled, e.g. by using an ORDER BY RANDOM on the database side while fetching the data for the corresponding file. Alternatively, returning them in the lexicographic order of the RPIs (which are random) is a valid option as well.
The possibility to identify temporary exposure keys belonging together (i.e. to the same user) is given, as they are posted together resulting in them being in a sequential order in the database. To prevent this, the aggregated files will be shuffled, e.g. by using an ORDER BY RANDOM on the database side while fetching the data for the corresponding file. Alternatively, returning them in the lexicographic order of the RPIs (which are random) is a valid option as well.
The configuration parameters mentioned above allow the health authorities to dynamically adjust the behavior of the mobile applications to the current epidemiological situation. For example, the risk score thresholds for the risk levels can be adjusted, as well as how the individual data from exposure events influence the overall score.
@ -225,7 +229,7 @@ If the backend calls from the mobile applications cannot be spread as evenly as
## Cross-border interoperability
A definite prerequisite for compatibility is, that the identifiers of the mobile devices can be matched, i.e. the API by Apple/Google is being used.
A definite prerequisite for compatibility is, that the identifiers of the mobile devices can be matched, i.e. the framework by Apple/Google is being used.
Further details will be added as soon as they are available.

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# Corona-Warn-App
<p align="center">
<a href="https://www.coronawarn.app/de/"><img src="https://raw.githubusercontent.com/corona-warn-app/cwa-documentation/master/images/CWA_title.png" width="400"></a>
</p>
<hr />
<p align="center">
<a href="#über-dieses-projekt">Über dieses Projekt</a>
<a href="#wer-wir-sind">Wer wir sind</a>
<a href="#danksagungen">Danksagungen</a>
<a href="#datenschutz">Datenschutz</a>
<a href="#code-of-conduct">Code of Conduct</a>
<a href="#arbeitssprache">Arbeitssprache</a>
<a href="#unsere-dokumentation">Unsere Dokumentation</a>
<a href="#lizenzierung">Lizenzierung</a>
<a href="#informationen-zur-teilnahme">Informationen zur Teilnahme</a>
<a href="https://www.coronawarn.app/de/">Webseite</a>
</p>
<hr />
HINWEIS: Die [englische Version](../README.md) der README-Datei ist die maßgebliche Fassung. Bitte haben Sie dafür Verständnis, dass die deutsche Version möglicherweise nicht durchgängig auf dem neuesten Stand ist.
## Über dieses Projekt
Wir entwickeln die offizielle COVID-19-App zur Kontaktfallbenachrichtigung für Deutschland, die sogenannte "Corona-Warn-App". Dieses Projekt hat zum Ziel, eine Anwendung auf der Grundlage einer Technologie mit einem dezentralisierten Ansatz zu entwickeln. Als Grundlage dienen die Protokolle [DP-3T](https://github.com/DP-3T/documents) (Decentralized Privacy-Preserving Proximity Tracing) und [TCN](https://tcn-coalition.org/) sowie die Spezifikationen für [Privacy-Preserving Contact Tracing](https://www.apple.com/covid19/contacttracing/) von Apple und Google. Wie DP-3T und TCN folgen auch die Apps und die Backend-Infrastruktur dem Open-Source-Prinzip - lizenziert unter [Apache 2.0 ](../LICENSE). Die Apps (für iOS und Android) werden pseudonymisierte Daten von Mobiltelefonen in der Umgebung mit Hilfe von Bluetooth-Technologie sammeln. Die Daten werden lokal auf den einzelnen Geräten gespeichert, um so den Zugriff auf die Daten und die Kontrolle über die Daten durch Behörden oder andere Instanzen zu verhindern. Wir erfüllen die geltenden Datenschutzvorgaben und garantieren höchste IT-Sicherheitsstandards. Auf diese Weise stellen wir uns den Datenschutzbedenken der Bevölkerung und hoffen dadurch, die Nutzung der Anwendung zu steigern.
Wir entwickeln die offizielle COVID-19-App zur Kontaktfallbenachrichtigung für Deutschland, die sogenannte "<a href="https://www.coronawarn.app/de/">Corona-Warn-App</a>". Dieses Projekt hat zum Ziel, eine Anwendung auf der Grundlage einer Technologie mit einem dezentralisierten Ansatz zu entwickeln. Als Grundlage dienen die Protokolle [DP-3T](https://github.com/DP-3T/documents) (Decentralized Privacy-Preserving Proximity Tracing) und [TCN](https://tcn-coalition.org/) sowie die Spezifikationen für [Privacy-Preserving Contact Tracing](https://www.apple.com/covid19/contacttracing/) von Apple und Google. Wie DP-3T und TCN folgen auch die Apps und die Backend-Infrastruktur dem Open-Source-Prinzip - lizenziert unter [Apache 2.0 ](../LICENSE). Die Apps (für iOS und Android) werden pseudonymisierte Daten von Mobiltelefonen in der Umgebung mit Hilfe von Bluetooth-Technologie sammeln. Die Daten werden lokal auf den einzelnen Geräten gespeichert, um so den Zugriff auf die Daten und die Kontrolle über die Daten durch Behörden oder andere Instanzen zu verhindern. Wir erfüllen die geltenden Datenschutzvorgaben und garantieren höchste IT-Sicherheitsstandards. Auf diese Weise stellen wir uns den Datenschutzbedenken der Bevölkerung und hoffen dadurch, die Nutzung der Anwendung zu steigern.
## Wer wir sind
@ -17,6 +34,10 @@ Wir möchten allen danken, die an diesem wichtigen Projekt gleich von Beginn an
In diesem Projekt berücksichtigen wir die Prinzipien der Datenschutzgrundverordnung (DSGVO), um die Privatsphäre aller zu schützen. Wir verarbeiten ausschließlich notwendige Daten und ausschließlich zu dem Zweck, alle wissen zu lassen, ob sie in engem Kontakt mit anderen, bereits infizierten Personen standen, ohne die jeweilige Identität zu offenbaren. Die Einhaltung dieser Grundsätze wird durch verschiedene Schritte sichergestellt, zum Beispiel durch die Implementierung technischer und organisatorischer Maßnahmen, die sich sorgfältig an die hohen Standards der DSGVO halten. Selbstverständlich wird die Anwendung eine verständliche Datenschutzerklärung vorhalten, um so transparent und klar wie möglich zu sein. Da wir die Anwendung als Open-Source-Projekt entwickeln, kann die Community dies überprüfen. Wir begrüßen Ihre Rückmeldungen!
## Code of Conduct
Dieses Projekt hat den [Contributor Covenant](https://www.contributor-covenant.org/) in Version 2.0 als unseren Code of Conduct übernommen. Bitte beachten Sie die Einzelheiten in unserem [CODE_OF_CONDUCT.md](../CODE_OF_CONDUCT.md). Alle Mitwirkenden müssen sich an den Code of Conduct halten.
## Arbeitssprache
Wir entwickeln diese Anwendung für Deutschland. Wir möchten so offen und transparent wie möglich sein, auch für Interessierte in der globalen Entwicklungscommunity, die nicht Deutsch sprechen. Daher wird sämtlicher Inhalt vor allem auf _Englisch_ zur Verfügung gestellt. Wir bitten auch alle Interessierten, Englisch als Arbeitssprache zu verwenden, etwa für Kommentare im Code, für die Dokumentation oder wenn Sie uns Anfragen senden. Die Anwendung selbst, die zugehörige Dokumentation und sämtlicher Inhalt für diejenigen, welche die Anwendungen nutzen, werden selbstverständlich auf Deutsch (und möglicherweise auch andere Sprachen) zur Verfügung gestellt. Wir werden auch versuchen, Entwicklungsdokumentation auf Deutsch zur Verfügung zu stellen, aber wir bitten um Verständnis dafür, dass es nur mit Englisch als der _Lingua Franca_ der globalen Entwicklungscommunity möglich sein wird, bei der Entwicklung dieser Anwendung mit höchstmöglicher Effizienz zu arbeiten.