Abstract:
Censorship systems such as the Great Firewall (GFW) have been continuously
refined to enhance their filtering capabilities. However, most prior
studies, and in particular the GFW, have been limited in scope and
conducted over short time periods, leading to gaps in our understanding of
the GFW’s evolving Web censorship mechanisms over time. We introduce GFWeb,
a novel system designed to discover domain blocklists used by the GFW for
censoring Web access. GFWeb exploits GFW’s bidirectional and loss-tolerant
blocking behavior to enable testing hundreds of millions of domains on a
monthly basis, thereby facilitating large-scale longitudinal measurement of
HTTP and HTTPS blocking mechanisms.