Using Google Pub/Sub as a rendezvous channel adds 7.17 seconds of bootstrapping overhead vs. a 1.32-second direct baseline when establishing a TorKameleon WebRTC bridge connection (total: 8.49s vs. 1.32s). The dominant bottleneck is subscription creation time (5.23s), not the message exchange itself (3.26s), averaged across 10 samples with 113 ms cross-Atlantic latency.

Separating the Broker role (a server that holds and manages bridge information) from both the rendezvous channel and the censorship evasion system enables modular protocol design: the rendezvous carrier can be swapped independently of the proxy system. The authors identify broker authentication and multi-broker load distribution as open problems not addressed in the current prototype.

§3.1, §5 defense

Google Cloud Pub/Sub is blocked entirely in China, limiting the system's applicability in the highest-censorship environment. Azure Pub/Sub is a structurally weaker candidate for rendezvous channels because each created resource receives a unique per-resource domain, enabling censors to block it with minimal collateral damage compared to blocking a shared Google or AWS endpoint.

§4.1 deployment

The paper surveys the rendezvous channel design space and identifies at least six prior carrier approaches: domain fronting via CDNs, AMP cache proxying, Amazon SQS queues, push notification services, email tunneling (Mailet, SWEET), and cryptocurrency covert channels (MoneyMorph). Pub/Sub adds bidirectional real-time messaging with broad IoT/enterprise adoption as a new carrier class not previously evaluated for circumvention rendezvous.

§2.2 defense

The system uses a shared Pub/Sub topic for all users, where session IDs (SIDs) are visible to all subscribers on the broker topic. The paper argues this does not compromise user anonymity because SIDs are randomly generated per-session by client-side software with no link to user identity, and all subsequent bridge-info payloads are encrypted under a session-specific symmetric key exchanged via asymmetric encryption.

§3.2 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

The host-profiling censor (passive traffic analysis: count connections per server, block those exceeding a threshold τ within a window w) blocks essentially all circumvention user traffic within 30 time steps for all classifier qualities tested (ρ_TP ∈ {0.9, 0.95, 0.99}), while causing far less collateral damage than zig-zag (never exceeding ~30% innocent server blocking). Snowflake resists this attack well: with w=3, τ=3, over 94.48% of users receive a proxy within 2 steps even with worst-classifier rules, and final unblocked server rates are 91.24–99.04%. The host profiling approach is feasible for passive censors who cannot enumerate the distribution channel.

2026-fares-game §5.2, Table 2, Table 3 traffic-shapeml-classifier

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