Information-Theoretically Secure Real-Time Voice Communication : An Experimental Study of QKD-Based Audio Transmission Using Opus

Sammanfattning

This thesis investigates the feasibility of Quantum Key Distribution (QKD)-secured real-time voice communication using One-Time Pad encryption. While QKD enables theoretically secure key exchange, the limited key generation rate introduces challenges for bandwidth-intensive real-time applications such as voice communication. To evaluate these challenges, a prototype voice communication system was designed and implemented using Opus audio compression, Real-time Transport Protocol-based transport, One-Time Pad encryption, and simulated QKD-generated keys. The system was experimentally tested and evaluated under varying audio bitrates and packet loss conditions. Performance was assessed using objective speech quality metrics, including STOI and PESQ, as well as latency, jitter, packet loss, and subjective intelligibility evaluations. The results show that low audio bitrates between 5 and 8 kbps provided the best balance between speech intelligibility and cryptographic sustainability. At higher bitrates, the limited QKD key generation rate caused significant packet loss due to key starvation, resulting in substantial degradation of audio quality. The system also demonstrated moderate resilience to packet loss at the identified viable bitrate. Furthermore, the addition of Wegman-Carter authentication introduced measurable but limited performance overhead in terms of latency and jitter. The findings indicate that QKD-secured real-time voice communication is technically feasible under constrained bitrate conditions, but that performance is strongly limited by the available key generation rate. The results further show that increasing bitrate or adding authentication overhead can lead to packet loss caused by cryptographic key starvation, which negatively affects speech quality and communication stability. The study highlights the trade-off between cryptographic security and real-time communication performance in QKD-based systems.