A central finding of the paper is that RFC-compliance in the censor creates evasion opportunities: the more faithfully a censor parses HTTP/DNS per the RFC, the more RFC-permitted variants it will pass that servers also accept, yielding more viable evasion strategies. In contrast, India's Airtel censor was the most brittle (56/77 strategies bypassed it) precisely because it failed on many legitimate RFC variants; China's more sophisticated parser left fewer openings.

Extending Geneva's genetic algorithm to the application layer automatically discovered 77 unique HTTP evasion strategies and 9 DNS evasion strategies against censors in China, India, and Kazakhstan — all requiring only unprivileged usermode modifications with no TCP/IP header access. Against India's Airtel censor, 56 of the 77 strategies succeeded; 29 worked against Kazakhstan; 22 evaded China's keyword-based HTTP censorship and 27 evaded its Host-header censorship.

§5.1, §6 evaluation

China's Great Firewall runs three independent DNS censorship injectors in parallel; elevating the DNS qdcount field to 2 (despite only one query being present, violating RFC 1035) evades all three injectors simultaneously with 100% success rate across 1,000 trials — but only Cloudflare (1.1.1.1) among eight tested open resolvers responds to such queries. DNS compression paired with an elevated qdcount also achieves 100% evasion of all three injectors but is supported only by Cloudflare and Google (8.8.8.8).

§6, Table 3 evaluation

China's GFW keyword-based and Host-header HTTP censorship can be simultaneously defeated by a 'sandwich' strategy: a header with a name ≥64 bytes must appear before the Host header, the Host header value must start ≥1,281 bytes from the start of the headers, and the final header must be ≥129 bytes total — and the Host header must not be first or last. A 64+ byte header name alone is sufficient to defeat Host-header censorship because it prevents the GFW from reading further headers.

§5.2 defense

India's Airtel HTTP censor fails to reassemble TCP segments: padding any HTTP request to at least 1,449 bytes causes the IP+TCP overhead (52 bytes) to push the total past the Ethernet MTU of 1,500 bytes, forcing segmentation that the censor cannot handle and achieving 100% evasion. Kazakhstan requires the segmentation boundary to fall precisely between the Host header name and value (with two trailing spaces), rather than anywhere in the request.

§5.2 evaluation

During the June 2025 shutdown, Iranian authorities blocked international One-Time Password (OTP) SMS delivery, preventing new sign-ins to foreign secure-messaging platforms and VPN services. This forced users toward government-approved domestic platforms that lack security and privacy protections. The blockade of OTPs effectively weaponized account-recovery flows as a secondary shutdown layer, disproportionately affecting users who needed to activate new circumvention tools during the crisis.

2025-iran-shutdown-measurement §Human Rights Implications port-blockingdpikeyword-filtering

Input blocking in Chinese LLM services (DeepSeek, Qwen, Kimi, Doubao) is overwhelmingly consistent: all four services persistently block the exact same queries across all 5 measurement samples in both Simplified and Traditional Chinese. Output blocking is far less consistent, with only 29 out of 349 output-blocked queries blocked across all 5 samples. Baidu-Chat is exceptional: it performs almost no input blocking but instead relies heavily on post-search and output blocking (78.6% of blocks are output-phase).

2026-ablove-characterizing §VI-B keyword-filteringdpi

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

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

All six Chinese browsers (Baidu Searchbox, UC Browser, QQ Browser, OPPO, Redmi/Mi, VIVO) transmit the full URL of every page visited—including HTTPS pages—along with page titles and search terms out-of-band to vendor servers, entirely bypassing VPN tunnel protection. In five of six cases this data is transmitted with no cryptography or weak cryptography (purely symmetric AES with hardcoded keys, or textbook RSA with a 128-bit modulus factorable in under 3 seconds), making it readable by any on-path actor between the VPN egress and the vendor's servers.

2025-rodriguez-revisiting §4.1 dpikeyword-filtering

All six browsers grant dangerous Android permissions (READ_PHONE_STATE, INTERNET, ACCESS_NETWORK_STATE) to third-party SDKs; built-in phone browsers grant significantly more such permissions than app-store browsers. Baidu Mobile Tongji Analytics SDK—present in all six via Baidu as default search engine—collects IMEI, UUID, CUID, GAID, device MAC, and Bluetooth MAC, creating a persistent cross-app device fingerprint that identifies users across VPN sessions and survives IP changes.

2025-rodriguez-revisiting §4.3 dpikeyword-filtering