2025-lu-rpki-based-location-unaware-tor
findings extracted from this paper
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.
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.
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.
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.
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).