TLS record fragmentation is implementable entirely in userspace at the application layer and requires no elevated privileges, unlike TCP segmentation which requires raw socket access. The authors' DPYProxy tool demonstrates a MITM approach that wraps TLS messages into smaller records before transmission without breaking the TLS handshake, since TLS records are unprotected during the handshake phase.

The GFW's SNI inspection is a stateless single-record parser: it cannot detect the SNI extension when the ClientHello is split across multiple TLS records, even when all records are contained within the same TCP segment. In contrast, the GFW does detect SNI when it appears fully within the first TCP segment despite TCP fragmentation, indicating the reassembly gap is specific to the TLS record layer.

§3 detection

TCP fragmentation before the SNI extension circumvents the GFW, but TCP fragmentation placing the SNI in the first TCP segment does not. The paper notes the GFW is showing 'the first signs of successfully handling TCP fragmentation,' indicating active hardening of TCP-layer circumvention that makes TLS-layer techniques increasingly necessary.

§3, Table 1 detection

96.21% of CitizenLab-tracked censored domains (1,092 of 1,135 scanned) and 92.36% of Tranco Top 1M domains (766,909 of 830,357 scanned) already support TLS record fragmentation, with support exceeding 90% across all Tranco rank ranges. This broad server-side compatibility makes TLS record fragmentation deployable without any server-side changes.

§4, Table 2 evaluation

TLS record fragmentation successfully circumvents the GFW in all tested configurations: splitting the ClientHello across multiple TLS records — whether the split falls before or after the SNI extension — bypasses GFW SNI-based blocking in every case (Table 1). TCP fragmentation after the SNI extension fails, but any TLS-layer fragmentation succeeds.

§3, Table 1 defense

The paper identifies a fundamental architectural vulnerability in single-IP circumvention designs: a relay must generate new observable flows (via DNS or TLS SNI) to reach end services after receiving client connections, creating a detectable server-and-client behavioral contrast. A relay accessing user-facing domains (news, social media) scores high on a Relay Suspicion Score (w=0.9) versus infrastructure domains (w=0.1). The paper argues this host-level signal is censorship-invariant and cannot be concealed by link obfuscation.

2026-almutairi-server §2.4, §4 traffic-shapedpisni-blocking

Article 19 documents that Iran's National Information Network (NIN / SHOMA) was designed with explicit reference to China's Great Firewall as a model, with institutional mirroring: Iran's Supreme Council of Cyberspace parallels China's Cyberspace Administration of China, and both governments share a "cyber sovereignty" doctrine used to justify domestic content controls and cross-border technology transfer. The report frames Iran's filtering infrastructure as deliberately architected to replicate GFW capabilities, not as an independently developed system.

2026-article19-tightening-the-net §2, §3 dpisni-blockingdns-poisoningip-blockingbgp-hijackthrottling

The report maps specific Belt and Road Initiative Digital Silk Road projects through which Chinese technology vendors have transferred censorship and surveillance infrastructure to Iran, including fiber backbone investments, data-center co-location agreements, and equipment supply chains. Specific vendors named include Huawei and ZTE as network infrastructure providers, with the report noting that equipment exports include filtering-capable hardware that Iran's ISPs have deployed at network choke points.

2026-article19-tightening-the-net §4, §5 dpisni-blockingthrottling

Despite AWS, Google, and Microsoft having publicly withdrawn CDN-level domain-fronting support to preserve commercial relationships with censoring states, domain fronting remains functional on AWS Lambda as of early 2026. Microsoft Azure Functions explicitly rejects mismatched SNI/Host headers, whereas AWS Lambda permits a client to present a legitimate *.lambda-url.*.on.aws SNI while routing internally to a different serverless function via the HTTP Host header.

2026-kang-censorless-serverless §4.7 sni-blocking

CensorLess vanilla mode costs $0.27/month for a single proxy processing 6.76 GB of traffic monthly, a 97.1% reduction (34.4×) over SpotProxy's optimal single-NIC configuration ($9.28/month). The private mode, which adds a t4g.micro EC2 VPS for end-to-end encryption via SOCKS, costs $3.41/month — still 63.3% cheaper than SpotProxy's cheapest option. Costs remain below $3.50/day even when scaling to 300 proxies.

2026-kang-censorless-serverless §6.3, Figure 6 ip-blockingsni-blockingdns-poisoning

Both Firefox and Chromium leak cleartext DNS before establishing encrypted DNS connections: they first send an unencrypted UDP DNS query to resolve the DoH server's domain (e.g., doh.opendns.com). An in-path censor can intercept and poison this initial query, making encrypted DNS in browsers completely ineffective without additional circumvention of the resolver-lookup step. Additionally, Chromium always includes the SNI extension in the encrypted DNS TLS handshake (e.g., "doh.opendns.com"), leaking the resolver identity even after the initial lookup. No resolver requires SNI to be present for certificate validation when the resolver's IP certificate is configured.

2026-lange-towards §2.4, §7, §10 dns-poisoningsni-blocking