Balancing privacy protecting and auditability: A signal protocol based E2EE communication scheme for group chatting

With the development of the Internet, instant messaging applications have ascended to a crucial position in our daily lives. As users increasingly attach importance to privacy issues, end-to-end encryption(E2EE) has become an indispensable requirement for messaging services. However, E2EE communication software face two major challenges. One is that completely being unregulated is rather perilous, as criminals may take advantage of it to cover up crimes and endanger society. Secondly, ordinary E2EE software only works between two parties, and there has been relatively little research on group chatting scenarios. Against these backdrops, this paper devises practical solutions to the problem of allowing audit access by authorized parties while safeguarding privacy in the context of group chatting. By leveraging the Signal protocol based on the open Noise protocol framework [1], we ingeniously transform the problem into multiple two-way chatting channels, thereby ensuring E2EE security and facilitating efficient group communication. Additionally, to address the auditing challenge, we delicately design the model with multiple cryptological techniques and safeguard the security of ordinary users while expediting the auditing process. This solution strikes a balance between privacy concerns and regulatory demands, and offers practical and innovative model design to secure group chatting, enhancing the usability and security of instant messaging applications.