[tor-dev] Feature Request: please consider ship default Tor bridges

[iry]

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David Fifield:
> On Thu, Aug 17, 2017 at 05:19:44PM +0000, iry wrote:
>> A set of Tor bridges are shipped with Tor browser bundle[0], 
>> helping users in Tor-censored area to connection to the Tor 
>> network. Since system Tor users may also face the censorship 
>> problem, shall we ship some Tor bridges along with the tor 
>> package?
>> 
>> The request is firstly reported[0] to Debian BTS and I got the 
>> following reply by Peter:
>> 
>>> If upstream starts shipping bridges with their Tor releases, 
>>> that would naturally result in the Tor package shipping
>>> bridges as well.
>>> 
>>> I do not know whether that's a good idea or not, but I don't 
>>> think deviating from upstream would be particularly 
>>> worthwhile.
> 
> To get an idea of how frequently the list of default bridges has 
> changed, see the tbb-bridges keyword in the bug tracker: 
> https://trac.torproject.org/projects/tor/query?keywords=~tbb-bridges&c
ol=time&col=id&col=summary&col=keywords&col=status&desc=1&order=time
>
>
> 
Thank you very much for informing us the way to check default bridges'
update frequency.

The frequency is generally once per month while sometime three times a
month.

This RSS feed may be helpful to immediately inform us the new changes:

https://trac.torproject.org/projects/tor/query?keywords=~tbb-bridges&for
mat=rss&col=id&col=summary&col=keywords&col=status&col=time&desc=1&order
=time

>> The default bridge shipped with tor package should be exactly
>> the same bridges contained in bridge_prefs.js[0] shipped with
>> the latest stable TBB. This is because: 1. The servers hosting 
>> default bridges are set up for huge amount of traffic; 2. The 
>> servers hosting default bridges are probably audited by TPO for 
>> better security; 3. Using a different set of bridges will 
>> distinguish the anon-connection-wizard bridge users from the TBB 
>> bridge users, which compromises their anonymity.
> 
> There is an argument for using a different set of default bridges: 
> when one of the Tor Browser ones gets blocked, it won't affect the 
> Debian ones. For example, for a while, Orbot had some additional 
> bridges that Tor Browser did not have. When the firewall of China 
> blocked the Tor Browser bridges, the Orbot ones continued working 
> for another nine months (until they got blocked for a different 
> reason). We know that at least China and Kazakhstan pay attention 
> to the default Tor Browser bridges (and China blocks them as soon 
> as they enter the source code, even before a release).

> So having a few bridges that are not shared with Tor Browser has 
> that advantage, at least.

Thank you for offering me the interesting information. I did not
realize this advantage before.

The advantages 1 and 2 which I mentioned above will still be valid as
long as the bridges are TPO proved. Therefore, it sounds to be a good
idea to have some unique bridges shipped with Debian Tor (if including
Tor bridges is a good idea).

> Of course, it's basically security by obscurity, because a censor 
> that can discover the Tor Browser bridges can (in theory) also 
> discover some other static list of bridges. But in practice it
> will take censors time to build automation to read from a new list,
>  default bridges are security by obscurity anyway, though 
> surprisingly effective for that.

That is true. Using security by obscurity strategy in censorship
circumvention is more like a resource competition. When the adversary
is a country like China, we may not be confident to win in long term.

Btw, Collateral Freedom seems to be one of the most effective ways to
circumvent Internet censorship in China. Circumvention tools that
depend on Collateral Freedom usually works fine, including meek,
lantern, psiphon3 etc. Therefore, I see a lot of potential work which
may benefit the Internet freedom in China. For example:
1. package meek into Debian
2. host (part of the) BridgeDB mirror on Github or AWS
3. #22402: https://trac.torproject.org/projects/tor/ticket/22402
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