BlueCoat's commercial DPI hardware/software, deployed in Syria, was confirmed capable of detecting and blocking Ultrasurf connections. BlueCoat logs recovered from Syria additionally exposed real Ultrasurf user behavior, including unproxied traffic leaking to non-Ultrasurf servers before and after bootstrapping completed.

An attacker with DNS spoofing capability — the paper cites the GFW explicitly — can respond to Ultrasurf DNS discovery queries before legitimate resolvers and inject crafted CNAME records that fully control the client's single-hop path selection. In code paths where peer verification is skipped ('SkipverifyQ0' log entries), this enables complete traffic interception without any cryptographic break.

§6.4, §5.6 detection

Ultrasurf confirmed to the researcher that its protocol has no forward secrecy and uses RC4 without any integrity check (no MAC or HMAC). This means all recorded ciphertext can be retrospectively decrypted once a session key is recovered, and the stream is trivially malleable — both properties confirmed by the UltraReach team during disclosure.

§8.1, §5.15 defense

Because Ultrasurf is a single-hop proxy where client ingress and remote web-server egress share the same IP address, any web server contacted through the network can log and report the proxy IP. The paper notes an attacker running a popular web server for a short time would passively harvest the full set of Ultrasurf server addresses for subsequent IP-list blocking.

§6.9 detection

Ultrasurf's DNS bootstrapping phase uses subdomain names that are always exactly 16 characters between delimiters and exclusively target .info TLDs, producing a constant byte-width network signature. The paper concludes that filtering this bootstrapping traffic is straightforward even without reverse engineering the client binary, as the client itself acts as a network discovery oracle for censors observing its connections.

§5.6, §6.8 detection

During the June 2025 Iran shutdown, circumvention tool performance diverged sharply by transport design. Psiphon's multi-protocol architecture sustained 1.5 million concurrent users—roughly one-third of its normal Iranian base. Lantern's "proxyless" protocol (domain-fronting via CDN, ~40% of Lantern's Iranian traffic) showed moderate success. Tor usage collapsed during the blackout but bridge connections surged and rebounded quickly after lifting. BeePass (serving 500k+ daily users at shutdown onset) used live A/B testing of port/obfuscation-prefix combinations to probe the censors' blocking parameters in real time. The Ceno Browser's P2P network grew from 600 active peers on June 13 to ~8,000 by July 11, indicating that decentralized fallback paths stayed up even during peak blocking.

2025-iran-shutdown-measurement §Tool Performance dpithrottling

The June 2025 Iran shutdown—carried out during the Iran-Israel war beginning ~June 19—did not use BGP route withdrawals as in 2019. Instead, authorities applied service-level restrictions at the national border: DNS poisoning of foreign destinations, protocol whitelisting permitting only pre-approved domestic services, and DPI to block circumvention-tool traffic. Iran's international traffic fell roughly 90% while the country's BGP routes remained advertised, making the shutdown invisible to BGP-based monitoring systems. OONI measurement volume, which totalled 121,333 in June 2025, collapsed to under 200 submissions on June 19-20.

2025-iran-shutdown-measurement Executive Summary / §2 dpidns-poisoningport-blockingip-blocking

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

A three-stage detection pipeline exploiting the "dual-role" behavioral fingerprint of single-IP circumvention relays achieved 23.2% recall (96/414 ground-truth relays) with a 0.18% false-positive rate against 97,651 benign TLS servers, for an overall accuracy of 99.5%. The ground-truth set covered OpenVPN, WireGuard, and SOCKS relays identified in a 17 TB single-day backbone trace (WIDE Project, April 9, 2025).

2026-almutairi-server §3.4, Table 1 traffic-shapedpiflow-correlation

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