A contact-tracing phone application and server that protects the privacy by using Homomorphic Encryption (HE) and Differential Privacy. HETracing was created as part of final year dissertation in order to discuss about the costs of using HE for contact tracing.

The app works for both iOS and Android and the front-end is written in Dart. The back-end server is written in Java. Three HE libraries can be linked to the phone application and server:

• SEAL
• Lattigo
• SMKHE

There are multiple steps to make the phone application and server build. The HE libraries need to be built for the phone platform that you want to use and also the server's platform.

To build for the server, you need to build the three HE libraries according to their specification. After this, you need to:

• Change lines 9-10 from this CMakeLists.txt file to specify the path of the smkhe library
• Change line 12 from this CMakeLists.txt file to specify the correct go path
• Run cmake . in he-component/bridge/server
• Run make in he-component/bridge/server

After these steps, the binary will be created in he-component/bridge/server and can be linked correctly from Java.

The server is also connected to a MariaDB database. To set the database, use the tables.sql file to create the tables needed by HETracing and then modify line 19 of the Controller file to point to the correct connection URL for the database.

Before building, modify line 4 from ConnectionService.swift, line 21 from ConnectionService.java and lines 6-7 from connection_service.dart to point to the right server IP. As in the case of the server, the first step is to build the three libraries for the phone's platform. After this, you need to link the binaries with CMake for Android or inside Xcode for iOS.

After building the binaries, you need to:

• Modify lines 24-26 from Makefile and line 7 from go.mod to point to the right paths
• Run make android inside he-component/src/client/lattigo/go
• Change lines 5, 6, 8, 9 from this CMakeLists.txt file to point to the binaries created for SEAL/SMKHE
• Run the application

You will probably need a developer account for notifications to work.

• Modify line 7 from go.mod to point to the right path and run make ios inside he-component/src/client/lattigo/go, creating the go library inside he-component/src/client/lattigo/go/build
• Inside Xcode, add the header and library search paths under Search Paths from Build Settings
• Inside Xcode, under Build Phases, go to Link Binary With Libraries and all the three libraries' binaries
• Run the application

HETracing using Firebase Cloud Messaging to send notifications from the server and the phone application uses the Google Maps API and Places API. To make the application work as expected, you will need:

• A Google API key that can be used for Maps and Places. You need to copy this in: line 18 of Android Manifest, line 7 of google_places.dart and line 36 of AppDelegate.swift
• For server, you need the FCM json file's path to be kept in environment variable GOOGLE_APPLICATION_CREDENTIALS and you need to specify the project id in line 20 of FCMNotificationManager.java
• For iOS, you need the FCM GoogleService-Info.plist placed in the root of the iOS project
• For Android, add the FCM google-services.json to the app folder