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The covid-19 app is capable of detecting who came into contact with who, how do they do it? I am trying to make something similar but I am unsure how they managed to get that information from the phones. I don't need the information to be private (like phone number), it could be something that only the government can make use of (like sim card number or MAC address. Is that possible?

I looked into Google Nearby and Wifi Direct... But as far as I understand it, it requires a handshake (covid19 app doesn't). I also looked into potentially making your phone into a hotspot and capturing wifi requests but I am not sure which library / API lets me do that.

Does anyone have know how this is done? I can't find a concrete answer anywhere, this seems to be actually impossible until I realized that the covid-19 app is doing it.

Ying Li
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    I believe the covid apps are advertising as BLE beacons or similar. Each covid-19 app scans for nearby covid-19 apps that are advertising, exchange tokens, and if you exchange enough tokens with another covid-19 app owner that later tests positive, your phone checks for a list of covid-positive tokens and tells you "the owner of a token I was near for 15 minutes tested positive, so you might be exposed". Your app could just similarly advertise via BLE and scan for its own advertisements from other people. – ArtHare Apr 28 '21 at 18:33
  • But that still requires the phone having the app, if you don't have the app, it can't track you? Won't that defeat the purpose of tracking if it requires permission? I thought the app would scan for "any phone" in the area and know which phone it's close to and record it. – Ying Li Apr 28 '21 at 18:35
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    The platform owners (Apple and Google) basically implemented the covid stuff at an OS level because of security/privacy concerns, so you probably can't reuse it. You _might_ be able to scan for the BLE emissions of the covid apps. And yeah, permissions can be a huge pain with BLE since it's considered tantamount to using fine location detection. – ArtHare Apr 28 '21 at 18:38
  • Have you seen: https://www.google.com/covid19/exposurenotifications/ as the various documents cover how Apple/Google are implementing the service. – Morrison Chang May 03 '21 at 04:31

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As Morrison Chang and ArtHare have commented already, Google and Apple have implemented this on an OS level:

In the coming months, Apple and Google will work to enable a broader Bluetooth-based contact tracing platform by building this functionality into the underlying platforms. (source)

If you want the specs they're using, Apple and Google have pages on how contact tracing is implemented, but it would be hard (if not impossible) for an app to implement this.

2br-2b
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