- anti-censorship-team - lists.torproject.org

Results of Turbo Tunnel security audit that affect Snowflake
by David Fifield 24 Apr '21

24 Apr '21

There was recently a security audit of Turbo Tunnel software artifacts, including dnstt and Snowflake. I posted the report on the dnstt page: https://www.bamsoftware.com/software/dnstt/cure53-turbotunnel-2021.pdf The report finds three issues that have to do with Snowflake, rated from Informational to Low. UCB-02-001: Memory leak in Handler() routine of Snowflake client library (Low) UCB-02-008: Lack of rate limiting in Snowflake and dnstt (Info) UCB-02-009: Brokers and proxies are not authenticated (Low) For UCB-02-001, I have already opened https://gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/snow…. UCB-02-008 is not a vulnerability, but only a suggestion that rate-limiting interactions may help mitigate certain kinds of resource-exhaustion attacks. Some related tickets are: "Broker needs better resilience against DoS" https://gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/snow… "Make it more expensive (CPU wise, or other thing) to make the initial connection to a snowflake" https://gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/snow… UCB-02-009 is something we have already discussed in the team across various issues. I don't know if we can meaningfully authenticate proxies, but the broker's messages ought to be signed and encrypted. "End-to-end confidentiality for Snowflake client registrations" https://gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/snow… "Authentication for proxy--bridge connections" https://gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/snow…

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Next anti-censorship reading group: 29 April 2021
by Cecylia Bocovich 22 Apr '21

22 Apr '21

Hey everyone! We will discuss "Domain Shadowing: Leveraging Content Delivery Networks for Robust Blocking-Resistant Communications" next Thursday at our regular team meeting on 2021-04-29, at 16 UTC. Relevant links: - https://www.usenix.org/system/files/sec21fall-wei.pdf Questions to ask and goals to have: - What can we learn from this work? - Are there immediate actions we can take based on this work? - Are there long-term actions we can take based on this work? - Is there future work that we want to call out, in hopes that others will pick it up? Hope to see you all there! Cecylia

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Crash in Snowflake users since 2021-01-17
by David Fifield 17 Apr '21

17 Apr '21

I happened to look at the Snowflake bridge's bandwidth and user history page, and the counts are close to zero since yesterday. I haven't investigated it at all. https://metrics.torproject.org/rs.html#details/5481936581E23D2D178105D44DB6…

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Throttling: What's old is new again
by Matthew Finkel 07 Apr '21

07 Apr '21

I found the premise of this article [0], that throttling connections (based on SNI) is new, a little amusing. It reminds me of how Iran implemented a very similar technique almost a decade ago [1]. I don't know of earlier uses of throttling as a censorship mechanism, at this scale, before the early-2010's (but I'd be interested in learning about them, if anyone knows). An earlier article about Roskomnadzor's implementation is interesting [2], for those who missed it. [0] https://arstechnica.com/gadgets/2021/04/russias-twitter-throttling-may-give… [1] https://ooni.org/post/iran-internet-censorship/#reported-cases-of-internet-… [2] https://arstechnica.com/gadgets/2021/03/a-russian-isp-confirms-roskomnadzor…

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Plans for Orbot and OnionBrowser domain fronting update
by Nathan of Guardian 02 Apr '21

02 Apr '21

It seems like Azure Domain Fronting may already be going offline, according to some reports. Our own testing from US and EU show that it is still working for now. That said, here is our plan for updating Orbot and Onion Browser in response to what may come at any moment: 1) Move to Fastly for Snowflake and Moat as soon as they are ready. Please keep us posted on this. 2) Remove Meek as a built-in option. 3) Promote "social distribution" of bridge URLs via links and QR codes through communities that need them 4) Work on setting up our own additional pool of CDN front addresses for Moat and the Snowflake broker(s) that we can round-robin/cat-and-mouse through for both Snowflake and Moat. These would be compiled into our apps, or provided through some kind of S3/hard to block bootstrap URL. 5) Continue our own work in mobile-specific bridge distribution (push messages, SMS, chat bots, social etc) options we can employ in the future. .... any other things to know, that we missed, that we are being naive about? Thanks! +n

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TurboTunnel Packet Scheduler Tips and Traffic Analysis Benefits
by Mike Perry 31 Mar '21

31 Mar '21

Hi all, I recently posted a draft proposal for traffic splitting for Tor: https://gitlab.torproject.org/tpo/core/torspec/-/blob/master/proposals/329-… It has similar properties as TurboTunnel, but I put quite a bit of work and consulted with several TCP and multipath TCP researchers to develop the packet scheduling algorithms defined in Section 3: https://gitlab.torproject.org/tpo/core/torspec/-/blob/master/proposals/329-… You may be interested in adopting those algorithms, if possible. There are variants that optimize for latency, throughput, or both in combination. The proposal also supports resumption of closed circuits. I am writing this mail because while these things are nice, resumption in particular does not defend against all classes of issues I am worried about with respect to confirmation attacks from closing or blocking connections, particularly onion service connections: https://gitlab.torproject.org/tpo/core/torspec/-/blob/master/proposals/329-… Briefly, if an adversary suspects an onion service is in use at a particular guard, it can make a circuit to that onion service, hold it open, and then close TCP connections of that guard to see if the circuit closes. This can even be done on the side with TCP RST injection, and possibly even blindly with brute force RST spoofing and spamming, if a good enough guess can be made about the IP address range of the service. Worse, in this case, the resumption I specified for Conflux does not help here, because this adversary will see the service's resumption attempt, and use that for confirmation instead of circuit close. TurboTunnel's resumption and automatic bridge discovery and replacement should greatly mitigate this attack, because it happens at a layer that is not necessarily controlled by the adversary, and thus resumption is mostly invisible to them (save for delay, which Cecylia is working on minimizing). Additionally, since traffic splitting has been shown to help against website fingerprinting, it stands to reason that doing traffic splitting at multiple layers and multiple endpoints may actually be better than doing it at just one layer, and costs us little-to-nothing in terms of overhead: https://www.comsys.rwth-aachen.de/fileadmin/papers/2020/2020-delacadena-tra… So please, keep on improving TurboTunnel! And let's compare notes about what we learn! Looking forward to obfs4 TurboTunnel, too! -- Mike Perry

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Ansible role that installs snowflake proxy on Debian
by Jacobo Nájera 17 Mar '21

17 Mar '21

Hi, I wrote an ansible role to install snowflake proxy on Debian Buster. I will extend its support to Fedora and Ubuntu and improvements soon. https://galaxy.ansible.com/nvjacobo/snowflake Repo: https://github.com/nvjacobo/snowflake Feedback is welcome Thanks, Jacobo

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No time change for the anti-censorship meeting
by Cecylia Bocovich 17 Mar '21

17 Mar '21

Hey everyone, We can discuss this at the meeting, but I'd like to keep the meeting time at 16 UTC regardless of the time change in places that recognize a difference between daylight savings and standard time. So, if you are in the US or Canada our weekly meeting will be at a different wall clock time. But it will be at the same time in UTC :) Hopefully see you there! Cecylia

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Next anti-censorship reading group: 4 March 2021
by Cecylia Bocovich 01 Mar '21

01 Mar '21

Hey everyone! We will discuss "Investigating Large Scale HTTPS Interception in Kazakhstan" this week at our team meeting on 2021-03-04, at 16 UTC. Relevant links: - https://censoredplanet.org/assets/Kazakhstan.pdf - https://censoredplanet.org/kazakhstan Questions to ask and goals to have: - What can we learn from this work? - Are there immediate actions we can take based on this work? - Are there long-term actions we can take based on this work? - Is there future work that we want to call out, in hopes that others will pick it up? Hope to see you all there! Cecylia

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Next anti-censorship reading group: 21 January 2021
by Cecylia Bocovich 20 Jan '21

20 Jan '21

Hey everyone! We will discuss "Early Detection of Censorship Events with Psiphon Network Data" two weeks from today at our team meeting on 2021-01-21, at 16 UTC. Paper link: https://tics.site/proceedings/2019a/icn_2019_7_10_38005.pdf Questions to ask and goals to have: - What can we learn from this work? - Are there immediate actions we can take based on this work? - Are there long-term actions we can take based on this work? - Is there future work that we want to call out, in hopes that others will pick it up? Hope to see you all there! Cecylia

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