  Tor provides anonymity to millions of users around the globe which has made
it a valuable target for malicious actors. As a low-latency anonymity system,
it is vulnerable to traffic correlation attacks from strong passive adversaries
such as large autonomous systems (ASes). In preliminary work, we have developed
a measurement approach utilizing the RIPE Atlas framework -- a network of more
than 11,000 probes worldwide -- to infer the risk of deanonymization for IPv4
clients in Germany and the US.
  In this paper, we apply our methodology to additional scenarios providing a
broader picture of the potential for deanonymization in the Tor network. In
particular, we (a) repeat our earlier (2020) measurements in 2022 to observe
changes over time, (b) adopt our approach for IPv6 to analyze the risk of
deanonymization when using this next-generation Internet protocol, and (c)
investigate the current situation in Russia, where censorship has been
intensified after the beginning of Russia's full-scale invasion of Ukraine.
According to our results, Tor provides user anonymity at consistent quality:
While individual numbers vary in dependence of client and destination, we were
able to identify ASes with the potential to conduct deanonymization attacks.
For clients in Germany and the US, the overall picture, however, has not
changed since 2020. In addition, the protocols (IPv4 vs. IPv6) do not
significantly impact the risk of deanonymization. Russian users are able to
securely evade censorship using Tor. Their general risk of deanonymization is,
in fact, lower than in the other investigated countries. Beyond, the few ASes
with the potential to successfully perform deanonymization are operated by
Western companies, further reducing the risk for Russian users.
