The speaker at the FOSDEM conference gave a talk about the introduction of post-quantum cryptography in the Linphone project's IP soft phone. The talk covered the RTP protocol and how it was modified to use post-quantum cryptography. The speaker also discussed the use of hybrid post-quantum and classical key exchange and provided some concluding remarks. The speaker mentioned that Linphone is an open-source project that has been around for over 20 years and supports SIP standards for audio, video, instant messaging, and secure group messaging. The speaker explained how the signaling path and media stream work in voice communication and the different options for exchanging symmetric keys. The speaker focused on the RTP protocol, which is based on Diffie-Hellman key exchange and explained how it provides end-to-end encryption without requiring a third party. The speaker then discussed the introduction of post-quantum cryptography in the RTP protocol and the challenges that arise from using key encapsulation mechanisms instead of Diffie-Hellman. The speaker explained the modifications made to the RTP handshake and the use of a hybrid approach that combines post-quantum and classical algorithms. The speaker also addressed the issue of packet fragmentation in the RTP protocol and how it was handled in the implementation. Overall, the talk provided an overview of the challenges and solutions involved in introducing post-quantum cryptography in voice communication.