TruzCall: Secure VoIP Calling on Android using ARM TrustZone

Use of mobile phones today has become pervasive throughout society. A common use of a phone involves calling another person using VoIP apps. However the OSes on mobile devices are prone to compromise creating a risk for users who want to have private conversations when calling someone. Mobile devices today provide a hardware-protected mode called trusted execution environment (TEE) to protect users from a compromised OS. In this paper we propose a design to allow a user to make a secure end-to-end protected VoIP call from a compromised mobile phone. We implemented our design, TruzCall using Android OS and TrustZone TEE running OP-TEE OS. We built a prototype using the TrustZone-enabled Hikey development board and tested our design using the open source VoIP app Linphone. Our testing utilizes a simulation based environment that allows a Hikey board to use a real phone for audio hardware.