An attacker can conduct stealth port scans against a victim without revealing their own IP by exploiting a 'patsy' host whose OS uses a globally incrementing IP Identifier: the attacker observes ID increments of 2 (rather than 1) in the patsy's traffic when the victim sends a RST to the patsy in response to a spoofed SYN, revealing open ports. Choosing a different patsy for each port makes the scan very hard to detect.

The user-level norm normalizer processes a realistic 100,000-packet trace (88% TCP) at approximately 101,000 pkts/sec (397 Mb/s) with all normalizations enabled on a $1,000 AMD Athlon 1.1 GHz PC, compared to a memory-copy-only baseline of 727,270 pkts/sec; the authors conclude a kernel implementation could sustain a bidirectional 100 Mbps access link with sufficient headroom to weather high-speed small-packet flooding attacks.

§7.2 evaluation

TCP RSTs are delivered unreliably and different OS stacks apply different validity rules, so a NIDS cannot safely tear down connection state on RST alone; a 'reliable RST' scheme — sending a keep-alive ACK behind every forwarded RST and tearing down state only upon observing a confirming RST from the trusted side — resolves this without violating end-to-end semantics. The cold-start problem (state loss on restart) can be addressed statelessly by stripping payload from unknown-connection packets from untrusted hosts and probing the trusted endpoint with a keep-alive before instantiating state.

§6.1–6.2 defense

Passive NIDS can be evaded via three fundamental classes of ambiguity: incomplete protocol analysis (none of the four commercial systems tested by Ptacek and Newsham in 1998 correctly reassembled IP fragments), divergent end-system behavior (different OS stacks resolve overlapping TCP retransmissions differently), and topology uncertainty (low-TTL packets may not reach the victim end-system, so the NIDS cannot determine which packets are delivered).

§1 detection

A traffic normalizer placed inline ('bump in the wire') can eliminate over 70 IP/TCP packet-level ambiguities before a NIDS inspects traffic — including fragment reassembly, TTL restoration, DF flag clearing, IP option removal, and cryptographic IP ID scrambling — leaving the classifier with an unambiguous byte stream and removing the degrees of freedom an attacker needs to evade detection.

§3, Appendix A defense

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

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

Amnesty International's 102-page investigation identifies a multi-vendor surveillance stack deployed in Pakistan: Chinese DPI (Geedge/MESA-derived), Canadian social-media monitoring (Netsweeper), and Emirati commercial spyware (Pegasus and FinFisher). The system enables deep packet inspection, SNI-based filtering, and traffic-shape classification at national scale, including targeted interception of encrypted messaging apps and VPN traffic.

2025-amnesty-pakistan-shadows §3, §5 dpisni-blockingip-blockingtraffic-shapeml-classifier

VPN search demand in Iran spiked approximately 707% during the June 2025 stealth blackout, as measured by Top10VPN analytics, making it one of the highest-documented circumvention-demand spikes associated with a single shutdown event. Despite this demand, many VPN connections failed because the protocol whitelist eliminated non-HTTPS tunneling methods and HTTP-level filters could detect known VPN signatures on port 443.

2025-aryapour-stealth-blackout §1, §5 dpiport-blockingtraffic-shape