In the fight against Covid-19, ContacTUM, an interdisciplinary research team at TUM, has developed a model for a contact tracing app that protects personal data. The concept is based on an encryption process that prevents the temporary contact numbers (TCNs) of infected individuals from ending up on the phones of their contacts. A prototype is now undergoing testing in cooperation with the ITO open Source Consortium. The app has also successfully completed the Bluetooth Special Interest Group qualification process. The members of the ContacTUM team come from the fields of informatics, physics, law, mathematics and medicine. Consortium members from the Department of Informatics are Prof. Dirk Heckmann (Chair of Law and Security of Digitization, joint appointment with TUM School of Governance) and Prof. Georg Carle (Chair of Network Architectures and Services).