Throttling Twitter: an emerging censorship technique in Russia

In March 2021, the Russian government started to throttle Twitter on a national level, marking the first ever use of large-scale, targeted throttling for censorship purposes. The slowdown was intended to pressure Twitter to comply with content removal requests from the Russian government. In this paper, we take a first look at this emerging censorship technique. We work with local activists in Russia to detect and measure the throttling and reverse engineer the throttler from in-country vantage points. We find that the throttling is triggered by Twitter domains in the TLS SNI extension, and the throttling limits both upstream and downstream traffic to a value between 130 kbps and 150 kbps by dropping packets that exceed this rate. We also find that the throttling devices appear to be located close to end-users, and that the throttling behaviors are consistent across different ISPs suggesting that they are centrally coordinated. Notably, this deployment marks a departure from Russia's previously decentralized model to a more centralized one that gives significant power to the authority to impose desired restrictions unilaterally. Russia's throttling of Twitter serves as a wake-up call to censorship researchers, and we hope to encourage future work in detecting and circumventing this emerging censorship technique.