Dynamic Quantum Group Key Agreement via Tree Key Graphs

Quantum key distribution (QKD) protocols are essential to guarantee information-theoretic security in quantum communication. Although there was some previous work on quantum group key distribution, they still face many challenges under a "dynamic" group communication scenario. In particular, when the group keys need to be updated in real-time for each user joining or leaving to ensure secure communication properties, i.e., forward confidentiality and backward confidentiality. However, current protocols require a large amount of quantum resources to update the group keys, and this makes them impractical for handling large and dynamic communication groups. In this paper, we apply the notion of "{\em tree key graph}" to the quantum key agreement and propose two dynamic Quantum Group Key Agreement (QGKA) protocols for a join or leave request in group communications. In addition, we analyze the quantum resource consumption of our proposed protocols. The number of qubits required per join or leave only increases logarithmically with the group size. As a result, our proposed protocols are more practical and scalable for large and dynamic quantum group communications.