A protocol-agnostic classifier that identifies RFC-mandated TCP behaviors (three-way handshake, 500ms ACK, 2×RMSS acknowledgement) leaking through UDP-based VPN tunnels achieves a false positive rate of 0.11–0.29% on real campus traffic, an order of magnitude lower than ML-based VPN detection techniques (FPR 1.4–5.5%) and on par with the GFW's estimated heuristic FPR of 0.6%.

The encapsulated TCP three-way handshake (3WHS) is detected in 80.59% of VPN flows but only 0.33% of plain UDP flows, making it—on its own—a near-practical VPN detector with 0.33% FPR; its presence is required by the classifier regardless of the compliance-rate threshold t.

§4.2 Feature Importance detection

ML-based VPN classifiers report FPRs of 1.4–5.5%, all exceeding the GFW's estimated practical threshold of 0.6%, while the simple RFC-heuristic approach achieves 0.11%; this indicates that real-world censors are more likely to adopt lightweight heuristic detectors than opaque ML pipelines.

§4.2 Overall Classifier Results evaluation

Random padding alone raises the classifier FPR only slightly (0.11% to 0.15%), and connection multiplexing alone raises it to 0.53%; however, combining both defenses raises FPR to 2.57%, making the detector impractical for a real-world censor and yielding TPR of 93.40%.

§4.2 Robustness of 3WHS / Table 3 defense

Web browsing VPN traffic achieves only 32.35–42.44% TPR—far below SSH (99.43–99.56%) and file transfer (83.95–99.73%)—because DNS queries interleaved with TCP streams disrupt detection of the encapsulated 3WHS, confirming that connection multiplexing is a naturally occurring and effective evasion for web-browsing workloads.

§4.2 Overall Classifier Results evaluation

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

AnyTLS's default padding scheme operates across 8 levels (stop=8), with initial padding fixed at 30 bytes, small-data padding 100–400 bytes, and medium-to-large data padding chains of 400–500 bytes continuing through multiple 500–1000 byte segments. The 'c' (continue) marker allows multi-stage padding sequences within a single connection burst.

2026-anon-anytls-anytls-sing-box-2026 §2.3 traffic-shapedpi

AnyTLS is a TLS-based proxy protocol maintained by the sing-box team, designed in 2024 and first released in the sing-box dev-next branch. Its core mechanism wraps arbitrary proxy traffic in standard TLS and applies a configurable padding scheme (Padding Scheme) to enhance traffic concealment while maintaining compatibility with standard TLS infrastructure.

2026-anon-anytls-anytls-sing-box-2026 §1.1–1.3 tls-fingerprinttraffic-shapedpi

Simulations extending the ENEM19 game-theory framework show that ephemeral proxy schemes (modeled on Snowflake/Lantern) effectively neutralize both the "optimal" and "aggressive" censors from the original framework. In overprovisioned settings (proxies arriving at 250/step vs. 200 clients/step), even the null censor scenario outperforms either censor in equal-arrival settings. Over 90% of waiting users receive a proxy within 1 time step. The critical variable is not censor sophistication but proxy arrival rate relative to client demand—high proxy churn combined with high arrival rate defeats both enumeration strategies tested.

2026-fares-game §4, Fig 1, Fig 2, Table 1 dpitraffic-shape

WebSocket, required by HTTPT and WebTunnel to establish covert channels inside TLS connections, had an adoption rate as low as 6.3% of websites in 2021, sharply limiting the pool of volunteer websites that can act as proxies for these tools. By contrast, Huma's traffic replacement scheme embeds covert data in standard HTTP leaf objects (images, scripts, CSS), requiring only that the DW serve HTTP content — a near-universal property.

2026-kamali-huma §II-C dpitraffic-shape