PTperf: On the Performance Evaluation of Tor Pluggable Transports

Zeya Umayya, Dhruv Malik, Devashish Gosain, Piyush Kumar Sharma

Abstract:

Tor, one of the most popular censorship circumvention systems,
faces regular blocking attempts by censors. Thus, to facilitate access,
it relies on “pluggable transports” (PTs) that disguise Tor’s traffic
and make it hard for the adversary to block Tor. However, these are
not yet well studied and compared for the performance they provide
to the users. Thus, we conduct a first comparative performance
evaluation of a total of 12 PTs—the ones currently supported by the
Tor project and those that can be integrated in the future.

Our results reveal multiple facets of the PT ecosystem. (1) PTs’
download time significantly varies even under similar network
conditions. (2) All PTs are not equally reliable. Thus, clients who
regularly suffer censorship may falsely believe that such PTs are
blocked. (3) PT performance depends on the underlying commu-
nication primitive. (4) PTs performance significantly depends on
the website access method (browser or command-line). Surpris-
ingly, for some PTs, website access time was even less than vanilla
Tor.

Based on our findings from more than 1.25M measurements, we
provide recommendations about selecting PTs and believe that our
study can facilitate access for users who face censorship.