IRBlock: A Large-Scale Measurement Study of the Great Firewall of Iran
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Presented at USENIX Security 2025 by
The Great Firewall of Iran (GFI) has evolved significantly over the past decade, constantly adding sophisticated blocking techniques. Prior research into Iran's Internet censorship, however, has primarily been one-off studies, leaving significant gaps in understanding the breadth and evolution of its filtering strategies. Exploiting the bidirectional blocking behaviors of the GFI and its own injection mechanisms as a side-channel to determine traffic disruption, we developed IRBlock, a novel large-scale, multi-protocol measurement system designed to measure DNS, HTTP, and UDP-based censorship across Iran, enabling continuous monitoring and in-depth exploration of the GFI's blocking behavior.