Hi all,
some of you might know Briar which uses Tor as its internet data transport. Currently, we only use direct Tor connections, but we also want the app to work where connections to Tor might get blocked.
Since we don't want all of our users go through bridges, we need to know where it is really needed, because we want things to work out of the box as much as possible. So I did some research and was surprised that there doesn't seem to be a maintained list of places where Tor is blocked.
Therefore, I looked into OONI vanilla_tor measurements from the past year and into the ratio of bridge users per country in the last three months with data from Tor Metrics. You can find the result here:
https://grobox.de/tor/ (needs JavaScript)
You will notice that Iran, Turkey and Venezuela are absent from both lists. Even China has a surprisingly high success rate. Do these countries maybe block the connections only later when the OONI probe doesn't listen anymore or is the blocking just very inconsistent? Tor Metrics also shows quite a few direct relay users in those countries.
So once we know where Tor is likely to be blocked, we would like to know where bridges will work and which kind. The only data source for this that we found are the OONI tcp_connect measurements. You can find our results from the past year here:
https://grobox.de/tor/bridges.html (needs JavaScript)
This is looking at TCP connection success rates in some pre-selected countries compared to a control group. Only China seems to be interfering with bridge connections, but not with all and not all the time.
When you only show Tor Browser bridges and even the ones with bad control group reachability, you will see that there's quite a few that perform very poorly. You might want to rethink including them.
If anybody finds these pages useful, I could set up a cronjob that automatically updates them.
I imagine that countries have other ways to interfere with bridge connections besides simple TCP blocking. If anybody is aware of reliable data sources for those, please let me know. Eventually, I would also be interested in knowing which pluggable transports work in which country. One-off academic research has limited usefulness here as we ideally have fresh data to decide parameters before each new Briar release.
Which bridges should we include in Briar? The first impulse is to just use whatever Tor Browser is using, but on IRC somebody told me that those bridges are already overloaded and that we better request some through the usual channels. Is that the recommended approach?
Thanks and Kind Regards, Torsten