Pathfinder: Exploring Path Diversity for Assessing Internet Censorship Inconsistency

Internet censorship is commonly enabled by authorities to enforce information control. So far, existing censorship studies have largely focused on country-level characterization, primarily because (1) censorship enforcement is often mandated through nationwide policies and (2) it is difficult to control the routing of probing packets to trigger censorship across different networks within a country. However, censorship mechanisms can vary significantly at the ISP level, revealing a more diverse landscape than previously assumed. In this paper, we investigate Internet censorship from a new perspective by scrutinizing diverse censorship deployments within a country. We design and deploy a measurement framework that utilizes multiple geo-distributed backend servers to probe various network paths from a single vantage point. By generating traffic targeting the same domain but different backend server IPs, we induce path diversity that exposes the traffic to distinct transit networks, and potentially, different censorship devices, thereby enabling a more granular analysis of censorship practices. Through our large-scale experiments and in-depth analysis, we reveal that diverse censorship resulting from varying routing paths within a country is widespread, implying that (1) the implementations of centralized censorship are commonly incomplete or flawed and (2) decentralized censorship is also prevalent. Moreover, we find that different hosting platforms also contribute to inconsistent censorship behavior due to their varying peering relationships with ISPs within a country. Finally, we present detailed case studies to illustrate the configurations that lead to such inconsistencies and to explore their underlying causes.