Dynamic Asymmetric Group Key Agreement Based on SM9 Signature

In 2021, the SM9 identity-based cryptographic algorithm became an ISO/IEC international standard, marking a significant advancement in China’s commercial cryptography technology and international standardization capabilities. The SM9 key exchange protocol, a component of the SM9 algorithm suite, provides secure communication by establishing a shared symmetric key between two parties. However, in a group of n users, directly applying this key exchange protocol requires each user to perform O(n) encryption operations and transmit an O(n)-sized ciphertext to ensure confidentiality, which becomes highly inefficient for large groups. To enable efficient secure group communication, we first develop a batch multi-signature algorithm based on SM9, and then we propose a dynamic asymmetric group key agreement (SMDAGKA) protocol based on this method. Our protocol reduces the required encryption operations and ciphertext size to O(1), significantly improving efficiency. Security proofs demonstrate that our scheme achieves a high level of security, and performance analysis shows that it incurs relatively lower computational overhead than related protocols.