Codar: COVID-19 Contact Tracer

This repository contains an implementation of an Android and iOS app to trace the spread of COVID-19 in a privacy preserving manner.

Backend docs

Encounters

An encounter has the following fields:

• timestamp unixtime timestamp of the moment the encounter occured (int)
• minDistance the smallest distance measured for the encounter in centimeters (int)
• duration the duration of the encounter in seconds (int)
• pid the pseudonymous identifier of the encoutered person
• reportType the reason for the encounter to be published. can be "SYMPTOMS_TESTED_POSITIVE" or "SYMPTOMS_TESTED_NEGATIVE" or "SYMPTOMS_NOT_TESTED".

Encounters are published by people who have reported that they are symptomatic.

location is currently not supported, the app can still collect location data on the client side

HTTP Api

All api functions are a available under https://europe-west1-chainbreaker-app.cloudfunctions.net/api. Authorization is done via an apiKey that should be included in every request using the Authorization HTTP header.
Example: Authorization: Bearer <apiKey>

GET /encounters?pids=pid1,pid2,...

Fetch all encounters that contain one of the pids listed in the pids parameter.
Request response example:

{
	encounters: [
			{
				timestamp: 2873642,
				minDistance: 100,
				duration: 121,
				pid: pid1
			},
			{
				timestamp: 2263745,
				minDistance: 50,
				duration: 43,
				pid: pid2
			},
			...
	]
}

From a privacy perspective this is not good, since we could match the reqeust IP with the provided pids and provided pids automatically become correlated which makes it useless to have changing pids in the first place.

POST /encounters

Post multiple encounters to the database.
Request body example:

{
	encounters: [
		{
			timestamp: 2873642,
			minDistance: 100,
			duration: 121,
			pid: some_random_pid
		},
		...
	]
}

GET /encounters/exports?startAfter=timestamp

Fetch references to the exports created by the exportEncounters cronjob ordered by creation time starting after startAfter.

Cronjobs

deleteEncounters

Every 24 hours a cronjob checks deletes encounters that are older than a month.
We could also anonymise the encounter by removing the pid instead of deleting it entirely.

exportEncounters (maybe not needed)

Every 24 hours a cronjob exports all new encounters to google cloud storage. All exported encounters are public and can be used by clients to search for matching encounters by themselves.