[tor-dev] DefenestraTor: Throwing out Windows in Tor

Roger Dingledine arma at mit.edu
Sun Mar 13 03:28:56 UTC 2011


"Tor is the most widely used privacy enhancing technology for achieving
online anonymity and resisting censorship. While conventional wisdom
dictates that the level of anonymity offered by Tor increases as its
user base grows, the most significant obstacle to Tor adoption contin-
ues to be its slow performance. We seek to enhance Tor's performance
by offering techniques to control congestion and improve flow control,
thereby reducing unnecessary delays.

To reduce congestion, we first evaluate small fixed-size circuit win-
dows and a dynamic circuit window that adaptively resizes in response to
perceived congestion. While these solutions improve web page response
times and require modification only to exit routers, they generally
offer poor flow control and slower downloads relative to Tor's
current design.  To improve flow control while reducing congestion,
we implement N23, an ATM-style per-link algorithm that allows Tor
routers to explicitly cap their queue lengths and signal congestion
via back-pressure. Our results show that N23 offers better congestion
and flow control, resulting in improved web page response times and
faster page loads compared to Tor's current design and the other
window-based approaches. We also argue that our proposals do not enable
any new attacks on Tor users' privacy.

I haven't read it yet, but figured I'd share it with others here in
the meantime.


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