My tasks were to write an application for Android platform which is able to secure VoIP communication with the ZRTP protocol and to understand the implementations of the protocol and the protocol itself. According to this I learned the protocols needed by VoIP, between them bigger emphasis investing in SRTP which provides security. After that I analyzed the ZRTP which provides confidentiality, protection against man-in-the-middle (MiTM) attacks and authentication for every media sessions. It makes these that it does not require support in the signaling protocol and the existing network.
After the analysis I planned a VoIP application with the judged for the best protocol implementation for devices that use Android operation system. With this application we able to communicate with others while we sure that nobody can eavesdrop our conversations. After the implementation of the planned program I tested its and the ZRTP protocol's operation with the test environment which I built. Examinations showed that not only I can talk with my application, but they proved the correctness of the protocol.