David Rupprecht, Katharina Kohls, Thorsten Holz, and Christina Pöpper Ruhr-Universität Bochum & New York University Abu Dhabi Introduction Voice over LTE (VoLTE) is a packet-based telephony service seamlessly integrated into the Long Term Evolution (LTE) standard. By now all major telecommunication operators use VoLTE. To secure the phone calls, VoLTE encrypts the voice data between the phone and the network with a stream cipher. The stream cipher shall generate a unique keystream for each call ...