On July 10, 2023, two members of this Open Collective project, David Fifield and Linus Nordberg, presented a research paper at the Free and Open Communications on the Internet (FOCI) workshop on the techniques used to make the Snowflake bridges scale to handle many users.
Running a high-performance pluggable transports Tor bridge
Abstract
The pluggable transports model in Tor separates the concerns of anonymity and circumvention by running circumvention code in a separate process, which exchanges information with the main Tor process over local interprocess communication. This model leads to problems with scaling, especially for transports, like meek and Snowflake, whose blocking resistance does not rely on there being numerous, independently administered bridges, but which rather forward all traffic to one or a few centralized bridges. We identify what bottlenecks arise as a bridge scales from 500 to 10,000 simultaneous users, and then from 10,000 to 50,000, and show ways of overcoming them, based on our experience running a Snowflake bridge. The key idea is running multiple Tor processes in parallel on the bridge host, with externally synchronized identity keys.