Never-twice avoidance — ensuring no country appears on both the entry leg (source→entry) and exit leg (exit→destination) of a Tor circuit — succeeds for 98.6% of source-destination pairs not in the same country, using only client-side RTT measurements. This directly defeats traffic-correlation deanonymization attacks that require an adversary on both legs of the circuit simultaneously.

DeTor circuits have significantly lower end-to-end RTTs than standard Tor circuits because high-RTT paths cannot satisfy avoidance proofs, effectively self-selecting for shorter routes. Bandwidth distributions are similar to standard Tor. However, intentional packet-delay defenses proposed for Tor (to defeat timing attacks) would increase effective δ and reduce DeTor proof coverage, creating a tension between delay-based anonymity defenses and RTT-based geographic avoidance.

§6.2.3, §6.2.1 (δ discussion) evaluation

Never-once avoidance succeeds for 75% of source-destination pairs that do not already terminate in the US (a highly routing-central country) at δ=0.5, and for nearly all pairs avoiding less central countries. Russia is the hardest case at ~35% success (δ=0.5) due to proximity to the dense European node cluster. The median successful source-destination pair has over 1,000 valid DeTor circuits when avoiding the US and 500 when avoiding China.

§6.2.1, §6.2.4 evaluation

DeTor proves geographic avoidance using speed-of-light RTT constraints rather than Internet topology maps. If the measured end-to-end RTT satisfies (1+δ)·Re2e < Rmin, where Rmin is the theoretical minimum RTT that would include any point in the forbidden region, then packets provably could not have traversed that region — even against adversaries who forge traceroute and BGP responses.

§3.1, §4.1 defense

Tor's built-in country-exclusion feature provides only the illusion of control: among circuits configured to exclude the US, only 12% could be identified as definitively avoiding US territory. The remaining 88% of 'trusted' circuits fail to deliver a proof of avoidance, meaning standard Tor policy and provable security diverge sharply.

§1, §6.2.1 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

Multi-censor simulations show that single-censor-optimized distribution strategies perform suboptimally in realistic multi-region deployments. When two networks have different censor strategies (e.g., one optimal, one zig-zag), the distributor cannot detect that a proxy is blocked until all censors have blocked it; this leaves clients without reachable proxies despite the proxy appearing "available" from the distributor's view. The authors conclude that "single-censor evaluation does not accurately predict more realistic deployment performance." A zig-zag censor in one region with 0.25 weight caused 44.4% collateral damage while reducing proxy lifetime to a median of 4 steps.

2026-fares-game §6, Table 4 traffic-shapeflow-correlation

The zig-zag traffic analysis attack (confirmed supported in Geedge TSG leak) rapidly enumerates all static proxy pools. With ζ_watch ∈ {4, 6} steps and a best-quality classifier (ρ_TP=0.99, ρ_FP=0.001), almost total proxy enumeration and user blockage occurs well before step 300. Even ζ_watch=2 leaves ~50% of users blocked. Collateral damage is high across all settings when ζ_watch ≥ 4: eventually ~50% of innocent servers are also blocked. However, Snowflake-style ephemeral proxies resist zig-zag effectively: reachability remains above 95% after 360 steps because churn prevents the censor from expanding its known proxy set beyond agents' direct assignments.

2026-fares-game §5.1, Fig 3, Fig 4 traffic-shapeflow-correlation

Per-flow RTTdiff detection rates are only ~20% because the majority of proxy flows connect to CDN-cached content (Cloudflare, Google, Fastly) that sits within 5ms of the proxy, suppressing the discrepancy. However, aggregating across flows per website visit yields detection rates exceeding 70%—and from the abstract, approximately 80% of top-5K domains generate at least one detectable flow—with half of those detections made within the first 60 packets. This means an adversary can reliably expose client and proxy IPs after just a few website visits.

2025-xue-discriminative §VI-C-2, Table II traffic-shapeflow-correlation

IMAP/SSL traffic on port 993 constitutes less than 1% of total ISP traffic but accounts for nearly one third of all false positives in the RTTdiff exploit, because IMAP's non-RESTful multi-connection pattern violates the request-response correlation assumption. The overall per-flow FPR is bounded at 0.6–0.7% (on par with GFW's estimated FPR against fully-encrypted proxies), but implementing a pre-filter to whitelist IMAP traffic reduces the FPR by approximately one third, making the fingerprint substantially more precise.

2025-xue-discriminative §VI-C-3, Table III traffic-shapeflow-correlation

Cross-layer RTT discrepancy (RTTdiff) is a protocol-agnostic fingerprint that exploits an inherent architectural property of all proxy setups: transport-layer sessions terminate at the proxy while application-layer sessions remain end-to-end. Evaluation across 10 proxy protocols—including VMess, Shadowsocks, VLESS, Trojan, XTLS-Vision, and obfs4-wrapped SOCKS—shows near-identical detection rates for all except obfs4, confirming the fingerprint is not tied to any specific obfuscation scheme. At FPR=0.01, per-website detection rates exceed 70% across all tested client and proxy location combinations.

2025-xue-discriminative §I, §VI-C traffic-shapeflow-correlation