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PrivEX - Privacy
by Tariq Elahi 27 Jun '14

27 Jun '14

tl;dr: We propose collecting data from exit nodes to improve the Tor network, using differential privacy and secure multiparty computation to do it in a privacy-sensitive manner. Hi tor-dev, In the ongoing effort to make Tor faster, secure and more resilient, network data plays an important role. If we know how the network is being used, what its clients' needs are and the threats that it faces we can deal with these in an intelligent manner. While the Tor Project does collect some statistics from guards, it does not currently collect and share potentially sensitive exit statistics. This data includes destination statistics and client timing behaviour, among many other potentially interesting, but privacy sensitive, data points. This reticence to collect data is due to the (well-founded) risk to clients and OR operators that this data could pose, such as correlation and coercion attacks. This is unfortunate since, as we observe above, in order to make improvements to the Tor network and its feature set, it would be beneficial to know what is going on inside it and with its users. To that end, it would be great if we were able to learn about network and client trend data. Some concrete examples include circuit-level data volumes, guard traffic usage, lengths of internal buffers, and latencies at relays. Indeed, if it can be counted then we should be able to collect and report it in a privacy-preserving manner. Which brings me to the reason for this email; I have had the good fortune to work with George Danezis at UCL and my supervisor Ian Goldberg at the University of Waterloo on coming up with a solution to this private data collection problem. We have created a system, PrivEx, that uses modern privacy-preserving techniques such as differential privacy and secure multiparty computation to address this thorny set of challenges; we have written up the details in a tech report that can be found here:http://cacr.uwaterloo.ca/techreports/2014/cacr2014-08.pdf . We have also created implementations of the two variants of PrivEx as described in the tech report. We are currently putting in the finishing touches and will be releasing them soon as open source in a git repo. We would like to start by rolling out our own PrivEx-enabled exits in the Tor network and begin collecting destination visit statistics. We expect that PrivEx will be generally useful to all exit operators and the Tor network in general but there is no requirement to deploy it everywhere. We hope to deploy PrivEx on a handful of exits during the June-August timeframe. What we would really like in order of importance is 1) a design review of our proposal, 2) an implementation review would be nice (once we release it). We hope that these reviews will address the main concerns of the community at large as well as give it, and us, a measure of confidence that collecting data with PrivEx is inherently good and is being done in a responsible and intelligent manner. We anticipate that this would make PrivEx an attractive addition for the Tor Project and their data collection needs. Please don't hesitate to give us your feedback, either to the list or to me via email. Cheers, Tariq

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Who shall we send to the GSoC reunion?
by Amogh Pradeep 25 Jun '14

25 Jun '14

Well, questions pretty straightforward, and I didn't get selected via the lucky draw, so I was thinking of alternative ways to get there!

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Fwd: Run a Small Tor Network for a Research
by Soroosh Sardari 25 Jun '14

25 Jun '14

Hi I want to run a small tor network with only 3 node, entry, router, and exit node. Also I want to set this three nodes in the client node without using directory server. Any idea appreciated. Regards, Soroosh

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Damian's Status Report - June 2014
by Damian Johnson 25 Jun '14

25 Jun '14

Oooh summer. Pollen scratching my eyes and a fiery ball of death hellbent on frying me. We oughta nuke the sun! Teach that lazy, freeloading ball of plasma who's boss. Just think of all the savings on air conditioning! In those rare moments not staving off heat stroke I spent much of this month visiting family, and just a tad on code... * Stem 1.2.0 introduced a couple version compatibility regressions, the first with python 3.x [1] and another with python 2.6 [2]. Both received hotfixes, bumping us now to version 1.2.2. * Karsten and I discussed a Python rewrite of ExoneraTor at length [3]. While this would be a pretty fun and interesting project, its relative impact compared to other things I have in the works right now isn't especially high. * Reviewed Stem usage in Kai's DetecTor project. [4] Recently I shifted my focus back to arm. I've been truly impressed at the level of interest in it on IRC! New arm users are appearing almost daily, and I owe them a shiny new release! [1] https://trac.torproject.org/projects/tor/ticket/12185 [2] https://trac.torproject.org/projects/tor/ticket/12223 [3] https://lists.torproject.org/pipermail/tor-dev/2014-June/006970.html [4] https://lists.torproject.org/pipermail/tor-dev/2014-June/006965.html

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Python ExoneraTor
by Damian Johnson 25 Jun '14

25 Jun '14

Hi Karsten. This is diving into enough detail that we might as well move this over to tor-dev@. For the list's benefit, Karsten and I are discussing a Python rewrite of ExoneraTor... https://exonerator.torproject.org/ https://gitweb.torproject.org/exonerator.git First I think I need to take a step back to figure out exactly what we're after. From a quick peek at ExoneraTor it looks like it behaves as follows... a. User enters an address (IPv4 or IPv6) and a date (either for a day or an hour). b. ExoneraTor lists router status entries for all relays that match the criteria. These entries link to the consensus they came from and server descriptors they reference. c. The user can then enter a destination address and port to search exit policies in TorDNSEL entres. Step 'a' and 'b' make sense to me. Step 'c' however I'm having a little difficulty groking. Ignoring TorDNSEL entries for a moment, we already have all the ingredients to provide the user with three fields to start with... * Source Address (required) * Timestamp (required) * Destination Address and/or Port (optional) The source address and timestamp come from the consensus, and an optional 'can it exit to destination X' consults the server descriptor's exit policy. So what is TorDNSEL providing us and why is it a separate search on the page? As I understand it the value of TorDNSEL is that we can't trust the address in the router status entries. If that's the case then our present search fields don't make sense to me... * Our initial search consults consensus information for the address and timestamp but not the exit policy. This is weird both because the address this has is faulty, and we have the exit policy so we could trivially include that in our search criteria. * Our second search gives the impression that we're using the earlier consensus results to query exit criteria from TorDNSEL. As I understand it though that's not what it's doing. TorDNSEL is completely independent from the consensus information. I could understand a search that just consults consensus information (ignoring address accuracy, it has everything we need). I could also understand a search that just consults TorDNSEL information (ignoring its inconsistent poll rate, it has everything we need). However, this hybrid approach and how it's presented really confuses me. Unless I'm mistaken with something above what I'd expect from ExoneraTor is... * The three search fields mentioned above. * It shows results based on the consensus information like we presently do. * If we have TorDNSEL entries that either indicate that a relay we're presenting had a different external address or another relay had the address we're searching for then note that. That is to say, the base search is based on consensus information (using server descriptor exit policies if we want to filter by that), and the TorDNSEL results are just appended notes since we can't rely on its poll rate. Thoughts? Cheers! -Damian PS. Congratulations on getting me invested. I just spent the last three hours in front of a whiteboard trying to puzzle out why ExoneraTor works the way it presently does. ;) PPS. Stem's ExitPolicy class has a can_eixt_to() method that would be really handy for this... https://stem.torproject.org/api/exit_policy.html#stem.exit_policy.ExitPolic… PPPS. I'm still hesitant about actually tackling this project. Arm is midway through being rewritten, and considering its sudden uptick in usage probably the most important project on my plate right now. That said, I'm happy to discuss this. Even if we don't implement it right now this thread will be useful so we know where we're going with ticket #8260. Concerning the earlier discussion of 'work with Karsten on a python project' I have a personal bias toward collaborating when the project has few unknowns for me, but working alone when *I'm* learning something. That is to say, I'd love to work with you on a straightforward Stem project and I'd also like to discuss ExoneraTor's design. But when it comes to coding, this has enough unknowns that if I take it on I'd prefer to experiment alone for a while - at least until I know enough about the APIs involved that I can avoid embarrassing myself. :) On Sun, Jun 8, 2014 at 2:56 AM, Karsten Loesing <karsten(a)torproject.org> wrote: > On 08/06/14 06:27, Damian Johnson wrote: >>>> Here's a quick overview of the codebase to facilitate reading through it: >>> >>> Ahhh, very useful - thanks. >> >> Hmmm. Just took a quick peek at the ExoneraTor codebase and, unless >> I'm mistaken, it doesn't actually use metrics-lib, does it? > > You're right, looks like it doesn't. > >> Honestly >> looking over the code is making me a little hesitant to take this on >> after all. I was anticipating a small, quick project of DocTor's scope >> but I've never touched SQLAlchemy or Posgress before. > > I don't think we'll even have to touch the Postgres for moving from Java > to Python. The Python code would simply do SQL calls via its SQL > library just like Java does. > > I just copied all SQL statements that the Python part would have to > prepare and execute: > > CALL insert_descriptor(?, ?); > CALL insert_statusentry(?, ?, ?, ?, ?, ?, ?); > CALL insert_consensus(?, ?); > CALL insert_exitlistentry(?, ?, ?, ?, ?); > SELECT MIN(validafter) AS first, MAX(validafter) AS last FROM consensus; > SELECT validafter FROM consensus WHERE validafter >= ? AND validafter <= ?; > CALL search_statusentries_by_address_date(?, ?); > CALL search_addresses_in_same_24 (?, ?); > CALL search_addresses_in_same_48 (?, ?); > SELECT rawdescriptor FROM descriptor WHERE descriptor = ?; > SELECT descriptor, rawdescriptor FROM descriptor WHERE descriptor LIKE ?; > SELECT rawconsensus FROM consensus WHERE validafter = ?; > > That's it. No further knowledge about Postgres required. > >> Once I wrote this I realized I'm being a damn hypocrite. Here I was >> saying "Karsten, learn Python so we can leverage each other's >> codebases!" but then I hightail it once the project delves into areas >> new to me. New arm users are showing up almost daily on irc and I'm >> anxious to give them a new release... but then this is exactly the >> issue, isn't it? Deliverables you'd like to focus on crowding out time >> to learn new things. >> >> So TL;DR I'm gonna eat my own words and suggest we focus on our >> separate domains for now. I really would like to work on some small >> metrics projects with you. Each month I eyeball your status reports >> asking myself "Is there anything here I can work with Karsten on to >> draw our spaces closer together?" so please let me know if you run >> across anything in Metrics we can collaborate on. > > (Replying below, first replying to the DynamoDB part.) > >> Your hypocritical friend, ~Damian >> >> PS. When we next meet I'd like to discuss ExoneraTor's design a bit. >> First thought I had when looking at the code was 'huh... I wonder if >> this would be a good use case for DynamoDB'. > > I'm wary about moving to another database, especially NoSQL ones and/or > cloud-based ones. They don't magically make things faster, and Postgres > is something I understand quite well by now. And again, I think that we > keep the Postgres part entirely unchanged when moving to Python. Not > saying that DymanoDB can't be the better choice, but switching the > database is not a priority for me. > > > So, regarding the rewrite: rather than canceling the project before it > starts, how about we find a role for you that you're more comfortable with? > > For example, I'd want to try rewriting it step by step based on your > suggestion of frameworks/libraries and with some code review of yours. > > If you're interested, which framework would I use for the new Python > ExoneraTor? It's supposed to do the following tasks: > > - Provide a simple web site with a web form, backed by the PostgreSQL > database. > - Maybe offer a simple RESTful API for lookups that the web form could > use to compose responses, but that could also be used by other > applications directly. > - Return documents from the database by identifier, so without > providing a search functionality. > - Run a scheduled task once per hour that fetches data from CollecTor > and puts it in a database. > > Bonus points if the result is as easy to deploy on Debian Wheezy as > possible. Like, install these few Debian packages, run the setup > script, done. > > Of course, if you'd prefer to focus on other things and not discuss > ExoneraTor stuff, that's perfectly fine, too. :) > > All the best, > Karsten >

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Reminder: tor dev IRC meeting each Wednesday (but not next week)
by Nick Mathewson 25 Jun '14

25 Jun '14

Hi, all! The next tor dev meeting is at the usual time: 19:00 UTC this Wednesday (June 25). This is the weekly IRC meeting for people working on the program "tor". (It won't cover all the other programs developed under the Tor umbrella.) (That's 3pm EDT and 12:00 noon PDT.) As usual, we'll do it on the #tor-dev IRC channel. (Also: we're not going to have one on Wednesday July 3: too many tor developers will be in France.) cheers, -- Nick

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GSoc update #2 - Stegotorus security enhancement
by Noah Rahman 24 Jun '14

24 Jun '14

Hello tor-dev. over the past two weeks I have - met with the team at SRI who have been developing further enhancements to stegotorus separately from the codebase available on github. We developed a plan to begin integrating the two codebases and to prepare it for integration with tbb and gitian builds as well (isis will hopefully advise us on the latter especially). To this end, I have established an Asana workspace specifically to cover the tasks needed for smooth integration (as opposed to the somewhat out of date individual tracs both sides were keeping) - implemented the Elligator handshake on a circuit level. I need to look into implementing it on a connection level to add greater security, as well as adding OCB encryption (does anyone know for sure whether this is in OpenSSL now? I can't seem to find out) - merged the config file code from SRI into our codebase. Multiple passphrase support should be added. - resolved nagging problems with our SWF Steganographic module architecture; the lessons learned should be helpful when integrating SRI's new JSON modulen. I intend to continue further work on this in person over the next month as well as at HOPE @ NYC in July, and a focused week in person with my mentor there should greatly speed progress. Best Noah R.

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Journey to the core of Tor: Why does Roger has so many guards?
by George Kadianakis 23 Jun '14

23 Jun '14

During our meeting in Iceland, we talked a lot about guard nodes. Some of that discussion eventually turned into proposal 236 [0]. During our discussions, we looked into the state file of Roger, and we noticed that there are 50 or so guard nodes in there. And that made us wonder: "Why does Roger have so many guards?". Roger is not the problem in this case; my state file also has many guards. Most people who don't use bridges or hardcoded EntryNodes have shitloads of guards. This post tries to explain why. So, Tor, in its memory, has an ordered list of entry guards (the global `entry_guards` smartlist in `src/or/entrynodes.c`). This list can be lengthy: it usually contains more than $NumEntryGuards entry guards. You can see this beautiful list just on your right below that beautiful stalagmite: https://gitweb.torproject.org/tor.git/blob/d064773595f1d0bf1b76dd6f7439bff6… This happens because in its first startup, Tor adds $NumEntryGuards nodes to that list. However if one of them is not Stable and Tor needs to build a Stable circuit, Tor will need to append a Stable guard to the list. Similarly, if one of the guards is down, Tor will need to compensate for that and append [1] one more guard to the list. The same happens if Tor needs to fetch directory documents, but its guards are not directory mirrors. So, if Tor walks to the end of the guard node list and it still hasn't found enough guard nodes with the needed property to make a pick, it picks a random entry guard from the consensus and adds it to the list. It's amazing and yet real, look straight ahead (and don't look directly into the light): https://gitweb.torproject.org/tor.git/blob/d064773595f1d0bf1b76dd6f7439bff6… But this still does not explain why Roger has so many guards. Usually a list of 5 or 6 nice guards is sufficient to satisfy the needs of any circuit (alive, stable, fast, directory mirror). The reason for Roger's surplus of guards, is the following very interesting functionality of Tor: Consider the following scenario, you start Tor while your network is down, Tor starts picking nodes from your list and attempts to connect to them. All connections fail, since your network is down. So now, Tor needs to add a new guard node to the list. There are two cases now: If Tor fails to connect to this new guard node (your network is still down), Tor removes the new guard node from the entry guard list (that's good; otherwise the list would be full of nodes added while the network is down). Look on your left, you can see this beautiful phenomenon happening here: https://gitweb.torproject.org/tor.git/blob/d064773595f1d0bf1b76dd6f7439bff6… However, let's say that your network is back up, and Tor manages to connect to this new guard node! That's great! But should Tor keep the connection to this guard? The answer is probably that it shouldn't: Tor should recognize this problem and attempt to reconnect to the primary guards on the top of the list. And that's exactly what Tor does. Nature is truly amazing! Just relax and witness this behavior happening right in front of your eyes: https://gitweb.torproject.org/tor.git/blob/d064773595f1d0bf1b76dd6f7439bff6… So, when Tor manages to connect to this newly added entry guard, it assumes that the network is back, and walks through the list of entry guards and marks them all as "needs to be retried". It also marks the connection to the new entry guard as rotten and kills it. This to me is very interesting, because it ensures that the primary guards (the ones at the top of the list) are going to be tried again after the network is back up; otherwise we would leak connections to new guards all the time! And all that fluff is related to this post, because this new guard (that made us realise that the network is back up) actually stays in our guard list. So, basically every time the network goes down and Tor does this little dance, a new entry guard is appended to our list and our statefile. And that's why Roger has so many guards! Or at least, that's why *I* have so many guards [2]. Apart from this being wonderful on its own, there are two interesting points here: a) There is always a bug: As this thing happens more times, our guard list gets bigger and the time to walk it increases. Dig this race condition: Tor starts up with the network being down, so the connections to our primary guards fail, but the network comes back while we are walking our entry guard list and trying to connect to the rest of our guards. If we manage to connect to one of the guards in our list (the lucky guard), the code at https://gitweb.torproject.org/tor.git/blob/d064773595f1d0bf1b76dd6f7439bff6… doesn't get triggered because `first_contact` is not true (that node was already in the guard node list). So, we stick with that lucky guard even though it's not our primary guard, and since the network is back up, a connection to our primary guards would work too. What stinks here is that all the guards above that lucky guard are marked as unreachable, so next time Tor starts up, it will ignore them and jump directly to the lucky guard. This probably needs to be fixed somehow. I opened trac ticket #12450 for this issue [3]. b) While writing proposal 236 we were thinking about how new guard nodes should be picked. Should we pick new guard nodes at the point they are needed? Or should we pick a surplus of guard nodes in the beginning, and then when the primary ones expire, we use the extra ones? You can read more about this behavior here: https://gitweb.torproject.org/torspec.git/blob/2ecd06fcfd883e8c760f0694f359… The insight here is that apparently we are already doing the latter approach, because all these guard nodes that get added when our network goes back up will remain in our guard list. And when our primary guards expire, the ones on the bottom will rise on the top (till they expire themselves). So if you are wondering "when does Tor add new entry guards?", the answer is "when you move your laptop to a new location; just before you connect to the wifi" ;) Greetings from the core, have a good day! [0]: https://gitweb.torproject.org/torspec.git/blob/HEAD:/proposals/236-single-g… [1]: Note that the word "append" is vital here. The extra guards are appended to the end of the list, and when Tor wants to pick a guard node it walks the list from the top. So, these newly added guards have lower priority so to say (most of them will not even be considered if the ones above are sufficient for building a circuit). [2]: Here is a grep of my logs. Look at how the guard counter increments by one everytime we hit https://gitweb.torproject.org/tor.git/blob/d064773595f1d0bf1b76dd6f7439bff6… $ zgrep "Marking earlier" /var/log/tor/notices.log.3.gz [warn] Connected to new entry guard XXX. Marking earlier entry guards up. 0/2 entry guards usable/new. [warn] Connected to new entry guard XXX. Marking earlier entry guards up. 0/3 entry guards usable/new. [warn] Connected to new entry guard XXX. Marking earlier entry guards up. 3/4 entry guards usable/new. [warn] Connected to new entry guard XXX. Marking earlier entry guards up. 4/5 entry guards usable/new. [warn] Connected to new entry guard XXX. Marking earlier entry guards up. 5/6 entry guards usable/new. [warn] Connected to new entry guard XXX. Marking earlier entry guards up. 8/9 entry guards usable/new. [warn] Connected to new entry guard XXX. Marking earlier entry guards up. 6/8 entry guards usable/new. [warn] Connected to new entry guard XXX. Marking earlier entry guards up. 7/9 entry guards usable/new. [warn] Connected to new entry guard XXX. Marking earlier entry guards up. 8/10 entry guards usable/new. [warn] Connected to new entry guard XXX. Marking earlier entry guards up. 9/11 entry guards usable/new. [warn] Connected to new entry guard XXX. Marking earlier entry guards up. 10/12 entry guards usable/new. [warn] Connected to new entry guard XXX. Marking earlier entry guards up. 11/13 entry guards usable/new. [warn] Connected to new entry guard XXX. Marking earlier entry guards up. 12/14 entry guards usable/new. [warn] Connected to new entry guard XXX. Marking earlier entry guards up. 13/15 entry guards usable/new. [3]: https://trac.torproject.org/projects/tor/ticket/12450#ticket

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GSoC: BridgeDB Twitter Distributor report
by Kostas Jakeliunas 21 Jun '14

21 Jun '14

Hi all, in the past couple of weeks I've been doing more of the same - namely, fleshing out churn control in the bot; finishing a generic challenge-response system (I'm also now considering making it into a Zope Interface); subclassed text-based challenge-response; incorporating isis' IRequestBridges and BridgeRequest's into the bot's bridge request processing part; and fake bridge-line-from-descriptor generator within the bot (didn't really do much re: the latter.) Unfortunately, all those parts are not yet ready for redeployment of the bot, and are either buggy or not finished (inclusion/use of BridgeRequests.) This is partly due to me having a bit less time in the last two weeks (a fault of my own; on the plus side, I've learned to use the soldering iron properly!) My plan is to finish the things that are near completion, and do another midterm-worthy status update "very soon." I'll also be present during the developer meeting hackdays (2th-4th), and hope to use them to flesh out ideas, etc. with isis/sysrqb. -- Kostas. 0x0e5dce45 @ pgp.mit.edu

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PT Combiner GSoC Second Report
by quinn jarrell 21 Jun '14

21 Jun '14

Hi, I'm the GSoC student working on creating a pluggable transport combiner. Progress: 1. I worked on modifying the SOCKS protocol to save the requested address and redirect the requester to a different address. 2. The pt combiner client side now starts a new chain of proxies in between the pts per connection instead of having to create a new set of pts per connection. 3. The pt proxies now shut down their ports after a single connection is established, lowering the number of ports needed. 4. Tested using authenticated pts and added a better logging mechanism. Quinn

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