Circumventing Psiphon Protective Measures Developed by Canada-based Psiphon Inc., Psiphon is a free and open-source internet circumvention tool designed to help users bypass online censorship and access restricted content. 75 Psiphon is primarily used in countries with significant internet censorship, including China, Iran, Egypt, and Turkey. 76 It has played a significant role in enabling access to censored information during times of political unrest, such as the 2021 Myanmar anti-junta protests and the 2021 Cuban protests. Psiphon3 employs a system known as Obfuscated Server Lists (OSL) to facilitate distributing server node information to clients. In contrast to other VPN applications, this server list is encrypted using a method referred to as server list encryption keys (SLOKs). The purpose of this encryption is to ensure that only trusted clients can access the complete list of server nodes, thereby preventing automated bots and opportunistic adversaries from scraping the information. According to the leaked data, Geedge Networks appears to have attempted to circumvent this protective measure by developing an internal tool referred to as Psiphon3-SLOK. This tool’s purpose is to continuously scrape the obfuscated server list and generates a compilation of IP addresses to be blocked, which is subsequently distributed to TSG nodes at client locations, through TSG Galaxy. In conversations with the Psiphon team, we learned that in late May of 2024 there was a sharp rise in users from Myanmar and a shift in how clients selected servers, consistent with server enumeration and targeted blocking. This period coincides with the deployment of the Geedge system in Myanmar. Internal data shared by Psiphon show that starting on May 30, 2024 Psiphon recorded about 500,000 new users. Myanmar traffic moved from a mix of discovery methods (REMOTE and EMBEDDED) toward mainly merit-based OBFUSCATED servers, indicating many servers were simultaneously blocked by certain ISPs. Although some servers were blocked, overall session quality, measured by tunnel duration and data transferred, remained normal. The duration and severity of blocking varied between ISPs. Psiphon employs a multi-layered server discovery process that allows clients to learn about available servers. Initially, EMBEDDED servers are included during installation, providing an immediate list of accessible nodes. Subsequently, DISCOVERY servers are fetched after an initial connection, expanding the client's access options. REMOTE servers can be accessed from a remote location, while OBFUSCATED servers are unlocked based on merit and are particularly resistant to enumeration and blocking due to their secure nature.

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