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use words API/framework correctly

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Thomas Klingbeil 2020-05-20 17:56:36 +02:00
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solution_architecture.md
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@ -33,11 +33,11 @@ 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") ![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. 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*). 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. sending 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. sending 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 user’s phone and is not shared. 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 user’s phone and is not shared.
@ -67,7 +67,7 @@ The flow for using the app is as follows, referencing the steps from *Figure 2*:
- **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 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 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 user’s 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). - **Step 4a:** After signing up for notifications in step 1, the user’s 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 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). - 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 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) - 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). - If the Corona-Warn-App Server receives a positive confirmation, the uploaded diagnosis keys are stored in the database (*Figure 3*, step 16).
@ -124,7 +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. 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. 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.
@ -229,7 +229,7 @@ If the backend calls from the mobile applications cannot be spread as evenly as
## Cross-border interoperability ## 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. Further details will be added as soon as they are available.