## 1 Introduction  
The use and importance of video conferencing systems are rapidly increasing in industry and academia due to the common preference for a remote environment. Security vulnerabilities in video conferencing systems have been exposed as their usage has increased. Hence, end-to-end encryption (E2 EE) stands out as one of the most pressing needs for enhancing security in video conferencing systems. E2 EE ensures that when two entities communicate, the contents of the message remain concealed from anyone except the intended recipient, preserving their confidentiality [1]. In order to address security vulnerabilities, video conferencing systems are currently implementing E2 EE security measures. Zoom, a video conferencing system popular in recent times, currently offers two phases of E2 EE security and has plans to gradually implement it across four phases. Additionally, they consistently share E2 EE security updates through whitepapers on their website [2]. Discussions of security services for video conferencing systems are actively progressing through the international standardization process for various technologies. A representative example is Secure Frame (SFrame), which is currently undergoing standardization [3]. SFrame is a group communication protocol that applies E2 EE security to a web real-time-communication (WebRTC) protocol that enables real-time communication. It provides E2 EE security by applying a double encryption method to a selective forwarding unit (SFU), an intermediate communication, in order to prevent the exposure of message information. Furthermore, SFrame uses a key management system for the E2 EE function for symmetric key sharing. Messaging layer security (MLS) is recommended for key management systems in standardization documents [3]. This is an E2 EE key management system, which is also undergoing Internet Engineering Task Force (IETF) standardization [4]. The SFrame group communication protocol has gained attention for significantly reducing communication overhead, a problem with E2 EE. SFrame is currently applied and used in video conferencing systems such as Google Duo and Cisco Webex [5]. In this study, the E2 EE-related protocols of Zoom and SFrame were investigated. Also, a detailed comparison between the two systems was conducted. The discussion focuses on the E2 EE protocols in a video conferencing system based on the Government Public Key Infrastructure (GPKI), which is known for robust reliability compared to authentication mechanisms used in the commercial sector. In particular, we propose a specific protocol that uses the key encapsulation mechanism (KEM) of post-quantum cryptography (PQC) for exchanging user keys in a GPKI-based video conferencing system. The proposed protocol does not expose the key to a central server because it securely shares the key through PQC KEM when a user enters a video conference. This protocol effectively fulfills authenticity, confidentiality, and integrity, which are the E2 EE security requirements [6]. To analyze the GPKI-based video conferencing system, we focused on the On-nara system in Korea [7]. In short, we compared the speeds of the proposed PQC KEM protocol, NTRU KEM, with the existing GPKI protocol, RSA 2048. Furthermore, we analyzed the security of PQC KEM for GPKI and made comparisons with Zoom and SFrame, which are used in the commercial sector. In Section 2, the research trends and security requirements regarding E2 EE security are explored, including an investigation into the security vulnerabilities of Zoom. In Section 3, an analysis is conducted on the key management system presented in Zoom's E2 EE whitepaper. Section 4 describes the structure related to the E2 EE function of SFrame and the E2 EE security key management system, MLS. Section 5 discusses the E2 EE protocol in the government user authentication mechanism and the GPKI-based authentication system.