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Hello Tor people!
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.
The following is some related information which may help the future discussion:
The possible formats to hold those bridges can be: 1. JSON which is also the way tor-connection-wizard used so far[1]; 2. plain text which is the same formatt given by the BridgeDB[2] by Tor Project; 3. "Bridge" + plain text which is ready to be appended to a torrc file or to be one of the torrc files in /etc/torrc.d/ (or whatever torrc.d path Debain decides to use)
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.
What do you think?
Looking forward to hearing your insights!
Best, iry
[0]: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=872456 [1]: https://gitweb.torproject.org/builders/tor-browser-bundle.git/tree/Bundl e-Data/PTConfigs/bridge_prefs.js?h=7.5a3-linux [2]: https://github.com/irykoon/anon-connection-wizard/blob/master/usr/share/ anon-connection-wizard/bridges_default [3]: https://bridges.torproject.org/options
Best, iry
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&col...
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:
- 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. 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.
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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
On Thu, Aug 17, 2017 at 07:57:53PM +0000, iry wrote:
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:
- package meek into Debian
- host (part of the) BridgeDB mirror on Github or AWS
- #22402: https://trac.torproject.org/projects/tor/ticket/22402
Some hopefully useful thoughts along these lines:
A) Most places around the world that need bridges these days need pluggable transport bridges, not just vanilla bridges. So if we want to bundle bridge addresses, we should bundle PT bridge addresses.
B) ...and that means we need to make sure that those PTs are well packaged in Debian too, since the Tor deb by itself would not be able to use them.
C) I wonder if we could use the new %include torrc directive in this situation: https://bugs.torproject.org/1922 That is, when you apt-get install obfs4proxy, is that the right time to populate /etc/torrc.d/obfs4-bridges with some (probably commented out to start) lines that let you use those bridges if you want?
--Roger
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David Fifield -
iry -
Roger Dingledine