A client-agnostic Discount Selection algorithm—discounting consensus weights of non-ROA-covered guard relays by factor d—achieves 90.2% of clients selecting ROA-protected guards at d=0.5 and 80% network load, an 18.8% improvement over vanilla Tor, with no measurable performance difference in Shadow simulation even at 100MB transfer sizes.

Location-aware Tor relay selection algorithms leak client AS-level location: an adversary observing 5 guard selections can guess the client's AS in under 10 attempts, and under 5 attempts after 15 selections. A chosen-destination attack exploiting guard selection bias finds the client's guard relay 94% of the time after 300 destination visits.

§2.1 detection

Shadow simulation at 10% Tor scale (719 relays, 75,234 clients) shows the Matching Selection algorithm adds 5.3% latency to circuit build time and 2.4% to round-trip time versus vanilla Tor; average overall transfer time is 1.8 seconds slower (out of 12 seconds baseline). For 100MB transfers—which occur rarely given the probability distribution of transfer sizes—the matching algorithm is 6.5 seconds slower on average and 15 seconds slower at median versus vanilla Tor's 31-second average.

§5.4 evaluation

A linear-programming Matching Selection algorithm pairing ROA-covered clients with ROV-enforcing guard ASes (and vice versa) achieves 48.47% of all client-relay pairs with full ROA+ROV protection using parameters l=0.8, d1=0.9, d2=0.7, B=1.5—a multifold increase over vanilla Tor's base rate. The algorithm is constrained so no relay exceeds θ=5× its vanilla selection probability, bounding guard placement attack risk.

§5.3 defense

ROA coverage of Tor guard relays grew steadily from 47.20% in January 2021 to 71.43% in May 2024 for IPv4, while IPv6 coverage grew from 19.41% to 43.89% over the same period. Overall ROA coverage for all Tor relays reached 83.51% by May 2024, with more than 90% of observed route announcements for covered prefixes being valid (reaching 92.91% for IPv4 guard relays in May 2024).

§3.2 evaluation

Article 19 documents that Iran's National Information Network (NIN / SHOMA) was designed with explicit reference to China's Great Firewall as a model, with institutional mirroring: Iran's Supreme Council of Cyberspace parallels China's Cyberspace Administration of China, and both governments share a "cyber sovereignty" doctrine used to justify domestic content controls and cross-border technology transfer. The report frames Iran's filtering infrastructure as deliberately architected to replicate GFW capabilities, not as an independently developed system.

2026-article19-tightening-the-net §2, §3 dpisni-blockingdns-poisoningip-blockingbgp-hijackthrottling

Comparative analysis of 73 unmatched events (2022 onward) between IODA's automated network-level detection and Access Now's #KeepItOn Shutdown Tracker reveals systematic documentation gaps — shutdowns recorded by human reporters are frequently absent from automated measurement platforms and vice versa.

2026-cheek-gaps-record-observability Abstract / §1 Introduction measurement-platformbgp-hijackactive-probing

HOWLR successfully detects 83% of the 1,902 real-world prefix hijack incidents observed in high-confidence Cloudflare Radar data from May 2026. The detection method fails when the hijacked prefix contains no authenticatable witnesses, and also cannot defend against routing adversaries capable of transparently forwarding non-targeted traffic within the prefix.

2026-doumanidis-howlr-client-driven-approach §4, §7 bgp-hijack

HOWLR's T4 variant (scanning only port 443) reduces worst-case prefix scan time from 260 minutes to 4 minutes while missing fewer than 2 witnesses in 83.6% of prefixes; the worst-case drop was 13 witnesses in a high-density prefix, still leaving 15 usable witnesses. Over a 6-day monitoring period, 96% of the 30,217-witness set maintained 99+% uptime.

2026-doumanidis-howlr-client-driven-approach §5, §6 bgp-hijack

HOWLR provides Light protection (≥3 witnesses in prefix) to 89% of Tor relay prefixes and Strong protection (≥8 witnesses from ≥2 CAs) to 64%, based on sampling 200 random relays. By contrast, DNS server prefixes receive Light protection in only 40% and Strong protection in only 12% of cases, reflecting their tendency toward residential or sparse hosting.

2026-doumanidis-howlr-client-driven-approach §6 bgp-hijack

BGP hijacking remains a practical threat to circumvention infrastructure: BGPWatch reported 5,673 possible hijack events in 2024 alone, and approximately 43% of ASes currently do not enforce route origin validation, leaving RPKI-covered prefixes still vulnerable. An attacker can statistically divert 50% of traffic by announcing an equally specific prefix with the genuine origin and itself prepended as next hop.

2026-doumanidis-howlr-client-driven-approach §2.2 bgp-hijackip-blocking