Exposure Notification API Support for Xamarin Apps

Jon Dick

Last month, Apple and Google announced plans for creating Exposure Notification APIs. By leveraging Bluetooth Low Energy, this help developers implement contact tracing for both iOS and Android. Our team has been tracking the releases of these APIs to ready them for Xamarin developers. Today, we are pleased to announce our first preview of bindings for the iOS and Android Exposure Notification APIs!

Cross-Platform Exposure Notification API

In addition to the core APIs, we have been prototyping a new, cross-platform API to simplify building contact tracing apps. A preview of this API is ready today! Find the project on the Xamarin.ExposureNotification GitHub repo. Below is more information about how Exposure Notifications work. As well as details on the cross-platform API we are building for developers.

Exposure Notification: Two devices sharing unique identifiers over bluetooth

How Exposure Notifications Work

Exposure Notifications rely heavily on generating and storing completely random rolling unique identifiers on a device. These are then broadcast to nearby devices. The devices detect nearby identifiers and store them as they enter into range (or contact) for up to 14 days.

A person will confirm a diagnosis by telling their device. It then anonymously submits the locally-stored, self-generated rolling of unique identifiers (from the last 14 days) to a backend service. This is provided by the app implementing the API.

Devices continually request the keys submitted by diagnosed people from the backend server. The device compares these keys to the unique identifiers of other devices in range from the last 14 days. Which it does to assess any potential risk of exposure. The app then prompts the user about potential exposure. Allowing the user to take appropriate actions to isolate themselves and monitor symptoms.

Learn More Today

Read more about the released first previews of:

Browse the bindings, cross-platform API, and “Getting Started” guides on the Xamarin.ExposureNotification GitHub repo.

Building an application using these APIs requires a secure backend for storing and processing unique identifiers. The team has put together a full sample powered by Azure Functions and Entity Framework. This sample is to be used as an example (not a reference) for building out a solution. Additionally, read through Google and Apple’s recommendations for securing notifications appropriately.


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  • Thornton, Wayne M 0

    My team with ViraTrace is looking at implementing a contact tracing solution that works cross-platform. Anyone we can talk to about the exposure notification APIs you developed in more detail?

    • redthMicrosoft employee 0

      Can you DM me @redth on twitter?

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