[tor-dev] Hello, I am a Tor Browser user in China. Currently, many obfs4 bridges are blocked by China's firewall.

Yawning Angel yawning at schwanenlied.me
Thu Oct 1 16:46:38 UTC 2015

On Thu, 1 Oct 2015 08:26:50 -0700
David Fifield <david at bamsoftware.com> wrote:
> I don't know about a schedule for deploying SkypeMorph and Dust. They
> may not help in your case anyway. The GFW is probably blocking the IP
> addresses of your bridges, not detecting the obfs4 protocol itself.

SkypeMorph: Never. (Licensing issues among other things)

Dust: I assume you mean Dust2, the original Dust is not getting
      deployed. Not sure yet.

[Folding in the 2nd reply]
> If you know some details of how I2P resists blocking, please add them
> to this wiki page:
> https://trac.torproject.org/projects/tor/wiki/doc/PluggableTransports

It doesn't do anything special.

The old TCP based protocol (NTCP) is trivially identifiable.

Blocking the more modern UDP protocol (SSU) would require looking for
high-entropy UDP or doing statistical attacks IIRC.  Active probing is
possible if they run a node that's part of the network and obtain
enough key material (But, I'd need to look at the floodfill system
again to figure out how many nodes for how long is realistically


Yawning Angel
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