[ooni-dev] Complete list of Tor blocking events

Sadia Afroz sadia.afroz at berkeley.edu
Mon Sep 29 20:30:48 UTC 2014

This has been very helpful.

Is there a way to get the help desk data? Is it available online?

On Mon, Sep 29, 2014 at 7:03 AM, Philipp Winter <phw at nymity.ch> wrote:

> On Thu, Sep 25, 2014 at 12:47:49PM -0700, Sadia Afroz wrote:
> > I am trying find a list of events when different countries blocked Tor to
> > understand why and how those countries blocked it and how Tor resolved
> > those issues. Do you know if anybody is maintaining such a list?
> Before the pluggable transports era, we tried to make Tor's link
> handshake look like a Firefox talking to a Web server [0].  It turned
> out that it's quite difficult to mimic TLS handshakes and some countries
> became good at fingerprinting Tor's TLS handshake.  Now that we have
> obfsproxy, the questions shifted from "how do we change Tor?" to "what
> additional pluggable transport do we need?".
> > I found censorshipwiki (
> > https://trac.torproject.org/projects/tor/wiki/doc/OONI/censorshipwiki)
> that
> > has a similar list. But it seems that it's not maintained any more as it
> > doesn't have the recent blocking incident by Iran. Also I'm not sure how
> > comprehensive is this list as it's missing Tunisia.
> The wiki does not have a well-defined set of maintainers and is indeed
> starting to collect some dust.  It's a community effort so please feel
> free to update it.
> > 1. Get the total number of Tor users from every countries over time and
> > look for anomalous fluctuations. When we created such a graph we noticed
> > that huge number of bot controlled nodes that appear in almost every
> > country's graph. It seems hard to identify real censorship events from
> > graphs like this that can be affected by other events unrelated to
> > censorship.
> Despite the spike caused by the botnet, it should still be possible to
> identify censorship events in the time series.  Censorship systems would
> likely not care if they block a genuine Tor user or a bot---as long as
> they don't target a particular Tor version.  As a result, I would still
> expect an effective censorship event to significantly reduce the total
> number of Tor users in a given country.
> > Let me know if there are other places I should look into to find
> censorship
> > events.
> Often, the help desk learns about censorship events first.  However,
> there's also some noise in help desk tickets as it's not always easy to
> distinguish between network issues and country-wide censorship.
> [0]
> https://trac.torproject.org/projects/tor/wiki/org/projects/Tor/TLSHistory
> Cheers,
> Philipp
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