Domain Shadowing: Leveraging Content Delivery Networks for Robust Blocking-Resistant Communications
Domain Shadowing: Leveraging Content Delivery Networks for Robust Blocking-Resistant Communications Mingkui Wei Cybersecurity Engineering George Mason University, Fairfax, VA, 22030 Abstract according to the Host header but have the TLS connection still appear to belong to the allowed domain. The blocking- We debut domain shadowing, a novel censorship evasion resistance of domain fronting derives from the significant technique leveraging content delivery networks (CDNs). Do- “collateral damage”, i.e., to disable domain fronting, the censor main shadowing exploits the fact that CDNs allow their cus- needs to block users from accessing the entire CDN, resulting tomers to claim arbitrary domains as the back-end. By set- in all domains on the CDN inaccessible. Because today’s ting the front-end of a CDN service as an allowed domain Internet relies heavily on web caches and many high-profile and the back-end a blocked one, a censored user can access websites also use CDNs to distribute their content, completely resources of the blocked domain with all “indicators”, includ- blocking access to a particular CDN may not be a feasible ing the connecting URL, the SNI of the TLS connection, and option for the censor. Because of its strong blocking-resistant the Host header of the HTTP(S) request, appear to belong power, domain fronting has been adopted by many censorship to the allowed domain. Furthermore, we demonstrate that evasion systems since it has been proposed [24, 28, 34, 36]. domain shadowing can be proliferated by domain fronting, In the last two years, however, many CDNs began to disable a censorship evasion technique popularly used a few years domain fronting by enforcing the match between the SNI and ago, making it even more difficult to block.
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