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One case that I remember when someone was unable to connect his bitcoin full node to the network because of censorship: https://twitter.com/TheBlueMatt/status/1161291626553270272

Matt suggested using TOR bridges for people who are unable to connect (directly/vpn/tor without bridges)

What are safer ways to connect to the Tor network so that you can use Bitcoin?

0

Tor and Bitcoin

Recently read one blog post which highlights the issues involved in using tor bridges and I will summarize few things that I found interesting:

  1. The author asks not to use unlisted or private bridges which is contrary to what Matt said in the above mentioned tweet in question.

  2. Harvesting the unlisted bridges: http://hackerfactor.com/blog/index.php?/archives/892-Tor-0day-Finding-Bridges.html

  3. Public bridges: Your Tor connection looks like thousands or millions of other users. This provides safety in numbers. In the worst case, an adversary can see that you are using Tor, but not what you are doing over the Tor network. Moreover, if you disconnect and then reconnect later from a different location, there is nothing linking your new connection to your previous connection; this mitigates the risk from tracking based on the connection method.

  4. Using Tor places you at risk sometimes: China India

  5. If Tor's use can be uniquely associated with you, then you are identifiable. Being identifiable means you may be monitored. How you connect to Tor allows you to be identified. In high-risk areas, using Tor makes you a suspect, and unlisted bridges make you easy to track. However, if you are arrested, then the official charge will probably on a non-Tor related topic (circumventing censorship, spreading unrest, etc.).

  6. Unlisted and Private bridge users are also the most at-risk because they are in censored areas that forbid direct and public bridge connections

  7. If they are blocking, then they are explicitly looking for Tor user.

  8. Internet disruptions in Belarus Internet shutdowns in India

  9. Unlisted bridge set is very distinct and effectively unique

  10. If you configured the Tor Browser to use bridges, then during the startup, it immediately connects to all of the configured bridges. An observer on the network will see connection requests from your current real IP address to the "very distinct and effectively unique" set of bridges. This allows an adversary that is tracking you to know that the IP address making the connection is explicitly you. Combined with historical sightings, they can determine when you first requested the set of bridges, where you were each time you accessed Tor, and where you are currently located.

  11. It doesn't disconnect from an established bridge connection until the browser shuts down. An adversary can see exactly which bridge set you had and to which set you switched.

  12. If all of your bridges match a set of bridges that I collected, then I know exactly which Tor exit node you were using and a timeframe when you were using it. While you are not unique, you are very distinct. This allows me to associate your real IP address with traffic from a known Tor exit node.

  13. Your set of unlisted (or private) bridges is stored to disk. If you use a system that never saves to disk, such as Tails, then you're fine. Just don't re-use bridge sets. But if you use the Tor Browser for the desktop or for mobile devices, then you are unique enough for tracking.

  14. The adversary has placed users in a corner: use Tor with unique tracking attributes, or don't use Tor. (Why are they not blocking all unlisted bridges? Maybe they don't have a LUB yet. Or maybe it is better to track and identify internal dissidents than it is to stop their connectivity. They may be intentionally blocking the safe and anonymous ways to connect to the Tor network in order to flush you out.)

  15. From a practical viewpoint, Tor users should consider the trade-off between discovery and connectivity. If you are in an environment that does not permit direct connections, and does not permit the public bridges, then it probably isn't safe enough to use the Tor network.

The blog post mentions usage of Tor browser which may not be the case when you are using Bitcoin full node with tor proxy on your machine. However lot of things mentioned are important if you are living in an area which has network censored by government regularly.

Source: http://hackerfactor.com/blog/index.php?/archives/893-Tor-0day-Tracking-Bridge-Users.html

Bridges can be configured using Tor browser in Windows or Ubuntu:

Tor-Browser-Bridges

Tails OS and few other Linux distros may have different settings to configure bridges: https://tails.boum.org/doc/first_steps/welcome_screen/bridge_mode/index.en.html

If you want to use bridges with torproxy, will have to add few things in /etc/tor/torrc file and you can compare the changes with a torrc file for Tor browser bundle:

torrc

Orbot on Android has the option to configure bridges:

Orbot-bridges

Setup docs related to TOR when using Bitcoin Core: https://github.com/bitcoin/bitcoin/blob/master/doc/tor.md

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