All 25 applicable client-side Geneva strategies failed when mechanically translated to server-side analogs against China's GFW, even when the only structural difference was which endpoint sent the insertion packet. Experiments with the server placed inside China and client outside also failed, indicating the GFW tracks connection initiator identity and processes client versus server packets asymmetrically—meaning server-side circumvention requires a completely independent discovery approach.

China's GFW uses distinct, co-located censorship boxes—each with its own independent network stack implementation and bugs—for each application-layer protocol it censors. TCP-level strategies that exploit transport-layer bugs show dramatically different success rates per protocol: Strategy 1 (Simultaneous Open + Injected RST) achieves 89% for DNS but only 14% for HTTPS; Strategy 8 (TCP Window Reduction) achieves 100% for SMTP but only 2–3% for DNS, HTTP, and HTTPS. TTL-limited probes confirm all protocol boxes are co-located at the same network hop.

§6, Table 2 detection

The paper identifies three distinct GFW resynchronization-state triggers with protocol-specific behavior: (1) a server payload on any non-SYN+ACK packet causes resync on the next SYN+ACK or client ACK-flagged packet for all protocols; (2) a server RST causes resync on the next client packet for all protocols except HTTPS; (3) a SYN+ACK with a corrupted acknowledgment number triggers resync only for FTP. Strategy 1's 50% per-attempt success rate for HTTP is confirmed to result from the 50% probability of the GFW entering the resynchronization state on an injected RST, consistent with Wang et al. [36].

§5.1 detection

The paper presents 11 purely server-side censorship evasion strategies requiring zero client-side software, successfully bypassing censorship in China, India, Iran, and Kazakhstan across DNS-over-TCP, FTP, HTTP, HTTPS, and SMTP. All strategies manipulate only TCP handshake packets (primarily the SYN+ACK) and were verified against 17 versions of 6 client operating systems (Windows XP–Server 2018, MacOS, iOS, Android, Ubuntu, CentOS) with unmodified clients.

§1, §5, Table 2 defense

TCP Window Reduction (Strategy 8)—reducing the SYN+ACK TCP window to 10 bytes and stripping wscale options, forcing the client to segment its request—achieves 100% evasion success against HTTP in India and Kazakhstan, 100% against HTTP and HTTPS in Iran, and 100% against SMTP in China, because none of these censors can reassemble TCP segments. The strategy is compatible with all 17 tested client OS versions when implemented without SYN+ACK payloads, making it the most broadly deployable server-side strategy found.

§5.1, §5.2, §7, Table 2 defense

Iran's censorship of refraction-networking proxies (Conjure via Psiphon) is not monolithic: different ISPs independently deploy different techniques and timelines. Over 800 million logged Conjure connections from July 2023–February 2025 across 10+ Iranian ASes show TCI (AS58224, ~33% of traffic) uses packet injection, while MCCI/Hamrah-e Avval (AS197207, ~22%) applies IP-based blocking, and some ASes (Parsonline AS16322, Shatel AS31549) show no proxy blocking at all.

2025-alaraj-iran-refraction §4 rst-injectionip-blockingpacket-injectiondpi

TTL-based path analysis showed that all censorship actions (DNS poisoning, HTTP injection, TLS resets) in the June 2025 shutdown occurred at the same network hop across all tested ISPs, indicating a single centralized national border gateway—likely TCI AS gateways—rather than per-ISP enforcement. Global BGP announcements were kept intact throughout, making the shutdown invisible to routing monitors while domestic connectivity collapsed.

2025-aryapour-stealth-blackout §4.5 dpidns-poisoningrst-injection

TLS connections to blocked services (instagram.com, telegram.org) were terminated by TCP RST immediately after the client's ClientHello, before any certificate exchange, confirming SNI-based DPI that reads the plaintext SNI extension and aborts the handshake. HTTP filtering additionally matched Host headers and URL keywords case-sensitively, with injected HTTP 403 pages or TCP RST responses, and case-change evasions were sometimes effective.

2025-aryapour-stealth-blackout §4.2, §4.3 sni-blockingdpirst-injectionkeyword-filtering

The August 20, 2025 unconditional RST event revealed an asymmetry in the GFW's triggering mechanism: for traffic originating inside China, both the client SYN and the server SYN+ACK each independently triggered three injected RST+ACK packets (six total per connection). For traffic to China from outside, only the Chinese server's SYN+ACK triggered RSTs — the foreign client's SYN alone was insufficient. This asymmetry implies the responsible device observed the SYN+ACK from the Chinese server as the trigger condition, not a port-match rule on the SYN.

2025-gfw-port443-rst §2.1, §2.2 rst-injectionport-blockingdpi

Iran's HTTP censor exhibits several parsing inconsistencies exploitable for evasion: (1) it is case-sensitive and ignores lowercase method variant "gET"; (2) it does not censor the Host header for HTTP version strings "HTTP", "1.1", and "example" (suggests a version regex of HTTP/.*); (3) when the Host header is absent, the path is not censored for versions "HTTP" and "HTTP/1"; (4) the body is never analyzed regardless of version. All HTTP and DNS censorship occurs at the same last-hop border node, suggesting centralized architecture.

2025-lange-i-ra-nconsistencies §3.2, Table 1 dpikeyword-filteringrst-injection

In China, multiple URLs show 100% failure rates across 3–7 ASNs with near-zero confirmed blockpage rates (e.g., hkleaks.ru, blockdx.co, libgen.space each at 100% failure, avg_confirmed ≈ 0), indicating that China increasingly uses non-blockpage mechanisms — connection drops, TCP anomalies — that evade blockpage-based detection while achieving complete access denial.

2025-lipphardt-1-800-censorship §4.4, Table 4 dpirst-injection