In mid-March 2020, literally on the first day of the government's corona lockdown, the SFB1258 scientists around Elisa Resconi asked themselves what they could do to help fight the corona pandemic. They started developing the concept for a Digital Contact Tracing Service (DCTS), an application that is commonly referred to as "Corona App" today.
The prime concern of the team was that the app ensures by design the maximum data security and privacy protection because they anticipated that the efficacy such an app could achieve would solely depend on the people's trust and acceptance in the tool. Thus, right from the beginning, they focused on a Bluetooth-based contact tracing system, that performs the matching between users who have the disease and their contacts on the non-infected users’ phones. This approach is known as the "decentralised" as opposed to the centralised, where the match is done on a central server.
A second activity developed around setting up an epidemiological model for simulating the effect of the app and other non-pharmaceutical mitigation measures with Monte Carlo methods. To achieve these goals, an interdisciplinary group of scientists from the SFB1258, the TUM Faculties of Mathematics, Physics and Computer Science and the TUM Schools of Medicine and Governance formed under the name of ContacTUM Consortium.
The ContacTUM team started a collaboration with ITO, a group of German professionals that joined to develop an open source contact tracing system, and got a member of the international TCN coalition, a community of technologists supporting privacy-preserving exposure notification apps during the Covid-19 pandemic.
The ContacTUM & ITO submitted their DCTS concept for review to the Bluetooth Special Interest Group (Bluethooth SIG) on 7 April. While the German Government initially favored the centralised over the decentralised approach for the German Corona app, a joint statement of international scientists was released on 19 April that urged countries "to rely only on systems that are subject to public scrutiny and that are privacy preserving by design". The statement was signed by the TUM scientists Prof. Christian Djeffal, Dr. Tina Pollmann, Prof. Elisa Resconi and Prof. Stefan Schönert, all of them engaged in the ContacTUM Consortium.
An app for android devices based on the ContacTUM & ITO concept is avaible for download on the ITO website since May. The publication that describes the principles of the ContacTUM & ITO DCTS "Digital Contact Tracing Service: An improved decentralized design for privacy and effectiveness" is available on GitHub and was submitted for publication. The concept includes the encryption technology Private Set Intersection Cardinality for improved privacy and second order tracing of contact persons. Detailed information on the DCTS app can be found on the following pages, including information on other DCTS approaches and on the apps officially provided in different countries.
Meanwhile, the German Government changed its mind and commissioned SAP & Deutsche Telekom with developing the official German app following the centralised approach. On 16 June, the German Corona-warn-app was finally released. We consider this as a big step, but our efforts continue. On a pure technical level, there is one aspect that still needs to be better understood: How reliable is the Bluetooth Low Energy signal as a measure of the distance? We are currently looking into this. But also privacy and data protection are issues we are still concerned with.
The results of the modelling were handed in for publication and are currently in the review process. We will report on the findings on these pages as soon as possible.