This repository contains an SDK for presence tracing based on the CrowdNotifier protocol.
CrowdNotifier proposes a protocol for building secure, decentralized, privacy-preserving presence tracing systems. It simplifies and accelerates the process of notifying individuals that shared a semi-public location with a SARS-CoV-2-positive person for a prolonged time without introducing new risks for users and locations. Existing proximity tracing systems (apps for contact tracing such as SwissCovid, Corona Warn App, and Immuni) notify only a subset of these people: those that were close enough for long enough. Current events have shown the need to notify all people that shared a space with a SARS-CoV-2-positive person. The proposed system provides an alternative to other presence-tracing systems that are based on invasive collection or that are prone to abuse by authorities.
The CrowdNotifier design aims to minimize privacy and security risks for individuals and communities, while guaranteeing the highest level of data protection and good usability and deployability. For further details on the design, see the CrowdNotifier White Paper.
Please see the links below for SDKs for other platforms:
- Android SDK: crowdnotifier-sdk-android
- iOS SDK: crowdnotifier-sdk-ios
- TypeScript Reference Implementation: crowdnotifier-ts
- Technical Specification for CrowdNotifier: techspec
You can find further information on the CrowdNotifier protocol in the CrowdNotifier white paper
The SDK is available on Maven Central and can be included directly as Gradle dependency:
dependencies {
implementation 'org.crowdnotifier:crowdnotifier-sdk-android:4.0.0'
}ATTENTION: Version 4.0 of the SDK is not backwards compatible with earlier versions!
// Get VenueInfo
VenueInfo venueInfo = CrowdNotifier.getVenueInfo(qrCode, host);
// Store a Check-In
long id = CrowdNotifier.addCheckIn(arrivalTime, departureTime, venueInfo, getContext());
// Update a Check-In
CrowdNotifier.updateCheckIn(id, arrivalTime, departureTime, venueInfo, getContext());
// Delete a Check-In
CrowdNotifier.deleteCheckIn(id, getContext());
// Match published SKs against stored encrypted venue visits
List<ExposureEvent> newExposures = CrowdNotifier.checkForMatches(publishedSKs, getContext());
// Get all exposureEvents
List<ExposureEvent> allExposures = CrowdNotifier.getExposureEvents(getContext());
// Clean up old entries
CrowdNotifier.cleanUpOldData(getContext(), 10);
// Remove an Exposure Event
CrowdNotifier.removeExposure(getContext(), id);
// Generate an Entry QR Code String
String entryQrCode = CrowdNotifier.generateVenueInfo(...).toQrCodeString("https://example-base-url.org");The CrowdNotifier class implements the following static methods that can be used to interact with the system. The SDK only stores encrypted entries of check-ins as well as exposure matches. Any additional storage of data needs to be handled by the app itself.
| Name | Description | Function Name |
|---|---|---|
| getVenueInfo | Returns information about the data contained in a QR code, or null if the QR code does not have a valid format | public static VenueInfo getVenueInfo(String qrCode, String host) |
| addCheckin | Stores a check in given arrival time, departure time and a VenueInfo object. Returns the id of the stored entry. | public static long addCheckIn(long arrivalTime, long departureTime, VenueInfo venueInfo, Context context) |
| updateCheckin | Updates a checkin that has previously been stored | public static boolean updateCheckIn(long id, long arrivalTime, long departureTime, VenueInfo venueInfo, Context context) |
| deleteCheckin | Deletes a checkin that has previously been stored | public static boolean deleteCheckIn(long id, Context context) |
| checkForMatches | Given a set of published events with a known infected visitor, stores and returns those locally stored check ins that overlap with one of the problematic events | public static List<ExposureEvent> checkForMatches(List<ProblematicEventInfo> publishedSKs, Context context) |
| getExposureEvents | Returns all currently stored check ins that have previously matched a problematic event | public static List<ExposureEvent> getExposureEvents(Context context) |
| cleanUpOldData | Removes all check ins that are older than the specified number of days | public static void cleanUpOldData(Context context, int maxDaysToKeep) |
| removeExposure | Removes the exposure with the given ID | public static void removeExposure(Context context, long exposureId) |
| generateVenueInfo | Generates a VenueInfo with the given properties. | public static VenueInfo generateVenueInfo(String description, String address, byte[] countryData, long validFrom, long validTo, byte[] masterPublicKey) |
| generateUserUploadPayload | Generates an anonymised Venue Visit which can be used for Backward-Tracing in the Backend. | public static UserUploadPayload generateUserUploadPayload(VenueInfo venueInfo, long startTimestamp, long endTimestamp) |
This project is truly open-source and we welcome any feedback on the code regarding both the implementation and security aspects. This repository contains the Android SDK, so please focus your feedback for this repository on implementation issues.
Before proceeding, please read the Code of Conduct to ensure positive and constructive interactions with the community.
This project is licensed under the terms of the MPL 2 license. See the LICENSE file.
The following list of apps are using this SDK: