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3581 discussions

Moving prop#250 discussion meeting to Tuesday, 1600 UTC
by Nick Mathewson 25 Jan '16

25 Jan '16

As mentioned on the other thread, George and David (who wrote proposal 250) can't make it at the originally planned time. So instead, we'll be discussing proposal 250 at 11 am eastern (1600 UTC) on Tuesday! (I'll still be around at the planned time to talk about patches and code and whatever.) cheers, -- Nick

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New Shadow versions now available
by Rob Jansen 24 Jan '16

24 Jan '16

Hello, Shadow versions 1.11.0 and 1.11.1 are now released! https://github.com/shadow/shadow/releases/tag/v1.11.0 https://github.com/shadow/shadow/releases/tag/v1.11.1 These versions represent a huge engineering effort to provide transparent support for plug-ins that use pthreads and that make blocking IO or system calls. We are using a fork of GNU portable threads (http://www.gnu.org/software/pth/) to enable this thread and blocking support. Shadow now literally just calls `tor_main()` and handles the rest internally. More details can be found in the release notes here: http://mailman.cs.umn.edu/archives/shadow-support/2016-January/000475.html All the best, Rob

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Proposal 251 (netflow padding) meeting logs, minutes, and action items
by Mike Perry 22 Jan '16

22 Jan '16

We had our meeting about the netflow padding defense proposal and implementation today: https://gitweb.torproject.org/torspec.git/tree/proposals/251-netflow-paddin… Here's the IRC logs: http://meetbot.debian.net/tor-dev/2016/tor-dev.2016-01-22-16.00.log.html The minutes+action item summary is as follows: - Write a torspec branch to describe the defense and changes since the proposal. The protocol changes will go in tor-spec.txt, and the behavior/usage will go in padding-spec.txt. Right now, I do not plan to also update Prop#251 itself, as the spec will be canonical. - In padding-spec.txt, we need to describe the options for disabling padding, reducing padding, and connection lifespan controls as these have changed since Prop#251 was written. - We are not going to use channel padding to obscure circuit setup (https://trac.torproject.org/projects/tor/ticket/17591), as fingerprinting is more of a risk from the guard node rather than someone watching TLS. It is better handled through multi-hop padding. That ticket needs to be closed or replaced with one to write a separate proposal for multi-hop padding. - We discussed overhead bounds and if we believe there are adversaries that exist that this will protect against (who won't/aren't doing full take for example). We believe data retention regulation and ISP practices strongly indicates that there are. - Bridges will be padded like clients are. - We discussed using behavioral checks to differentiate clients from relays instead of the consensus checks. I do not like this option, as it introduces protocol side effects that seem sloppy and prone to cause problems in the future (like CREATE_FAST did). I am not sure if we came to an agreement here. - We need to be sure to describe the protocol negotiation and forward compatibility properties of the padding negotiation in detail in tor-spec.txt. After the meeting, Nick and I discussed some implementation details. We need to improve the callback handling and maybe also upgrade libevent's timer algorithm. Nick is working on a new data structure to look up channels in O(1), so we can fix a callback channel dropping bug he spotted in code review, and eliminate the need to reach into channeltls_t from channelpadding.c. Nick also has code review comments in https://trac.torproject.org/projects/tor/ticket/16861#comment:39 that I have mostly fixed, minus the callback issue. I will be posting a reply and a new branch later today. I think that's it. Please reply with questions, comments, or additions, or if I missed anything. -- Mike Perry

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Entry/Exit node selection
by Evan d'Entremont 22 Jan '16

22 Jan '16

What threat is Tor trying to defeat? Region locking or nation states? If the former, then great, select an exit country, or just use a VPN. If the latter, perhaps that actual threat profile should be taken into account. Is there any reason why Tor doesn't select exit nodes which are as close as possible to the intended host? If I connect to Tor and request a resource from a server on ISP A, would in not make sense to enforce an exit node also on ISP A, or if not, as close as possible? As well, entry guards should be as close as possible to the user, limiting the ability of others to log the connection. In short, it's safer that only my ISP see a connection rather than my ISP, a backbone provider, the entry guard's ISP, etc. Systems like XKeyscore wouldn't even see the traffic in this case. It seems that selecting an exit country may actually be detrimental to anonymity by forcing traffic over the (monitored) internet backbone. Evan d'Entremont

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SyslogIdentityTag considered to be backported to 0.2.7?
by nusenu 21 Jan '16

21 Jan '16

Hi, I like weasel's [1] SyslogIdentityTag feature that is available in debian 0.2.7 packages only. The ticket [1] suggests that it will be included in tor 0.2.8.x (milestone). Would you consider to backport it to 0.2.7 as well so other platforms can make use of it before we see tor 0.2.8 (without having to ask every package maintainer to maybe ship packages with the patch applied)? thanks! [1] https://trac.torproject.org/projects/tor/ticket/17194 https://gitweb.torproject.org/debian/tor.git/tree/debian/patches/20-upstrea…

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Is it possible to specify voluntary delays in my Tor client?
by Virgil Griffith 20 Jan '16

20 Jan '16

I.e., if I want the extra resistance to traffic analysis that higher latency connections provide, is there a way to specify that in my Tor config? -V

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Notes from 1st Tor proposal reading group [prop241, prop247, prop259]
by George Kadianakis 19 Jan '16

19 Jan '16

Today was the first Tor proposal reading group [0] and we discussed the following guard proposals: Prop#241: Resisting guard-turnover attacks [DRAFT] Prop#259: New Guard Selection Behaviour [DRAFT] Prop#247: Defending Against Guard Discovery Attacks using Vanguards [DRAFT] In this mail, I will assume that the reader is familiar with the concepts behind those proposals. We started by discussing prop241 and prop259. These proposals specify how Tor should pick and use entry guards. - We decided that we should merge the remaining ideas of prop241 into prop259. - prop259: The original guardset should also include 80/443 bridges (shouldn't have disjoint utopic/dystopic guard sets). We should specify a behavior on how the fascist firewall heuristic should work. - prop259: Should probably not impose a specific data structure to the implementor except if strictly required. Instead maybe state the properties that such a data structure needs. Maybe we can put the hashring idea in the appendix? - We can simulate the various algorithms we are examining to test their behavior and correctness. Nick and Isis have already written some guard switching code to be simulated: https://github.com/isislovecruft/guardsim.git However, no simulations happen right now. We should code some simulation scenarios and check that the algorithm works as intended in all possible edge cases: https://github.com/isislovecruft/guardsim/blob/master/doc/stuff-to-test.txt We then moved to discussing prop247. Proposal 247 specifies how entry guards should be used by hidden services to avoid various attacks: - We can think of prop241 as the proposal specifying how entry guards work on Tor. It specifies how Tor selects its set of guards and also how it picks and switches between them. Then prop247 could be stacked on top of prop241 specifying how entry guards are used specifically in _hidden services_ and describing how the guardsets from prop241 can be used in the hidden services setting. To achieve this design we should figure out what we need from Tor guardsets to achieve all the needs of prop247, and then we should design the interface of guardsets appropriately in prop241. A stupid Guardset interface that prop247 could use could be: guardset_layer_1 = Guardset(nodes_to_consider, n_guards=1, rotation_period_max, flags, exclude_nodes) guardset_layer_2 = Guardset(nodes_to_consider, n_guards=4, rotation_period_max, flags, exclude_nodes=guardset_layer_1) - We discussed how the HS path selection should happen in prop247. Should layer-2 and layer-3 vanguards be picked from the set of Guard nodes, or should they be middle relays? This is important to figure out both for security and performance! Also, it's clear that layer-2 vanguards should not be the same node as the layer-1 guard. But what about layer-3 vanguards? Can they be the same node as the layer-1 guard? If not, then an attacker learns information about the layer-1 guard by keeping track of the list of layer-3 vanguards by monitoring many layer-3 rotations. Also, should layer-3 guardsets share nodes between them or should they be disjoint? We should be very careful about what kind of relays we allow in each position since it's clear that it has security implications. We should edit the proposal and specify this further. - We should test our design here with a txtorcon test client, and get some assurance about the performance and correctness of the system. Also, we need to see how CBT interacts with it. If you want to help with any of the above, show up for the little-t-tor meeting tomorrow. --- [0]: https://lists.torproject.org/pipermail/tor-dev/2016-January/010219.html

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Re: [tor-dev] Does Orbot use default obfs4 bridges?
by Nathan Freitas 19 Jan '16

19 Jan '16

On Tue, Jan 19, 2016, at 03:33 PM, David Fifield wrote: > On Tue, Jan 19, 2016 at 03:29:38PM -0500, Nathan Freitas wrote: > > > > On Tue, Jan 19, 2016, at 02:52 PM, David Fifield wrote: > > > Does Orbot have a list of default built-in obfs4 bridges? Or do users > > > fetch them dynamically? I looked in the source code and found default > > > meek bridges but not default obfs4. > > > > No we have no default Obfs4 bridges built-in. It has been on my list to > > get done, because we really should, obviously to make the user > > experience better, and to alleviate meek traffic. > > > > > I'm asking because we recently added a few new high-capacity default > > > obfs4 bridges. > > > https://bugs.torproject.org/18071 (1 bridge) > > > https://bugs.torproject.org/18091 (2 bridges) > > > > I will get this built-in ASAP. > > The list of Tor Browser built-in bridges is here: > https://gitweb.torproject.org/builders/tor-browser-bundle.git/tree/Bundle-D… Fantastic. Those will be built into the next release.

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ENGINE_get_default_ECDx missing?
by Gisle Vanem 19 Jan '16

19 Jan '16

Seems these two OpenSSL functions: ENGINE_get_default_ECDSA() ENGINE_get_default_ECDH() have been dropped; in util/libeay32.num: ... ENGINE_get_default_ECDH 3387 1_1_0 NOEXIST::FUNCTION: ENGINE_get_default_ECDSA 3662 1_1_0 NOEXIST::FUNCTION: ... https://raw.githubusercontent.com/openssl/openssl/master/util/libeay.num (not sure exactly what 'NOEXIST' does). So shouldn't common/crypto.c be patched into something like: --- a/src/common/crypto.c 2016-01-14 22:29:59 +++ b/src/common/crypto.c 2016-01-18 17:55:53 @@ -373,8 +373,10 @@ used by Tor and the set of algorithms available in the engine */ log_engine("RSA", ENGINE_get_default_RSA()); log_engine("DH", ENGINE_get_default_DH()); +#if OPENSSL_VERSION_NUMBER < OPENSSL_V_SERIES(1,1,0) log_engine("ECDH", ENGINE_get_default_ECDH()); log_engine("ECDSA", ENGINE_get_default_ECDSA()); +#endif log_engine("RAND", ENGINE_get_default_RAND()); log_engine("RAND (which we will not use)", ENGINE_get_default_RAND()); log_engine("SHA1", ENGINE_get_digest_engine(NID_sha1)); Isn't OpenSSL 1.1.0 supported yet? Scratching head... BTW, I'm using TDM-gcc 5.1 (http://tdm-gcc.tdragon.net/) on Win-10. -- --gv

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Re: [tor-dev] Does Orbot use default obfs4 bridges?
by Nathan Freitas 19 Jan '16

19 Jan '16

On Tue, Jan 19, 2016, at 02:52 PM, David Fifield wrote: > Does Orbot have a list of default built-in obfs4 bridges? Or do users > fetch them dynamically? I looked in the source code and found default > meek bridges but not default obfs4. No we have no default Obfs4 bridges built-in. It has been on my list to get done, because we really should, obviously to make the user experience better, and to alleviate meek traffic. > I'm asking because we recently added a few new high-capacity default > obfs4 bridges. > https://bugs.torproject.org/18071 (1 bridge) > https://bugs.torproject.org/18091 (2 bridges) I will get this built-in ASAP. +n

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