tor-dev March 2016

tor-dev@lists.torproject.org

75 participants
71 discussions

How to build a Router that will only allow Tor users
by Martin Kepplinger 20 Mar '16

20 Mar '16

Hi, I try to configure OpenWRT in a way that it will only allow outgoing connections if it is Tor. Basically it is the opposite of "blacklisting exit relays on servers": "whitelisting (guard) relays for clients". It should *not* run Tor itself. A first test setup (onionoo document, ipset and iptables) kind of worked. It's definitely doable, but not totally trivial in the end. What did *not* work, was starting Torbrowser. That's a hard requirement, and before bebugging it through I ask: Do I miss something when I just allow outgoing connections to * Guard, * Authority, * and HSDir flagged relays (do I *need* them? that's a different question probably) I don't restrict ports for now, even though I really should, and it's all only IPv4 addresses I care about for now, and I easily could just have OpenWRT configured wrongly, but: DNS is not an issue I think, what else could be? So far I only see Torbrowser talking to one Authority while starting. thanks martin

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Scheduling next proposal discussion meetings
by Isabela 20 Mar '16

20 Mar '16

Hello there, on today's irc meeting we choose 2 proposals to discuss: #224 and #267. I took a look at people's availability in the wiki and picked the following date&time for both meetings: * Proposal 224: Next-Generation Hidden Services in Tor o Wednesday, March 16th 2200 UTC (teor can join) o Must-have attendees: special, dgoulet, asn, teor o Conflicts: (If you are noting a conflict, please include a big bunch of times when you COULD make it.) + ??? o Can-attend: * Proposal 267: Tor Consensus Transparency o Friday, March 18th 1600 UTC o Must-have attendees: ln5, leif o Conflicts: (If you are noting a conflict, please include a big bunch of times when you COULD make it.) + ???? o Can-attend: Please update in the wiki with your options for them. If this date and time does not work, let me know what is a good one in the 'conflicts' notes. https://trac.torproject.org/projects/tor/wiki/org/teams/NetworkTeam/Meeting… Let me know if you have any questions! cheers, Isabela -- PM at TorProject.org gpg fingerprint = 8F2A F9B6 D4A1 4D03 FDF1 B298 3224 4994 1506 4C7B @isa

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Core Tor / Network Team meeting time updates.
by Nick Mathewson 19 Mar '16

19 Mar '16

Hi, all! I've got a doodle poll open on http://doodle.com/poll/nvx26m4cxspryf3e to try to find the best time for a network team meeting. So far, it looks like our options are somewhat constrained, since we have people who are living from UTC-7 through UTC+11, and a wide range of time zones in between. (Karsten has said he's okay with us picking a time he can only-sorta make. Isabela claims she has no sleep schedule and can meet whenever.) In particular, we're going to have a hard time having both George and Teor on the same meeting, since whenever they're both available, all the west-coast-US people are asleep. Asking people to start meetings before 0800 or after 2200 in their personal time zones is not IMO nice or okay, so let's not try to do that. So, my favorite option ("Find some magical time when everybody can make it") is out. So, as I see it here are our options: A. Pick a time when as many people as possible can attend. Include people who can't make that time by doing one or more of these: A1. Encourage everybody to catch up informally with everybody who can't attend. A2. Work with the people who can't attend, and whoever has a schedule closest to theirs, to make sure that there is a supplemental topic meeting on topics of their joint interest. A3. In addition to meetbot logs, keep minutes of the meetings and send them to tor-dev. B. Try to pick two or more times such that everybody can make one or the other. Try to solve disconnectedness by doing one or more of these: B1. Encourage everybody who can attend both to do so. B2. Make Nick and Isabela attend both. B3. Try to make sure there are at least 3 times, with several people shared pairwise between each. B4. Minutes as above. C. We all move to a nice tropical island. Thoughts? Especially from regular attendees or would-be-regular attendees? peace, -- Nick

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Meeting about the new guard algorithm proposal (prop259)
by George Kadianakis 19 Mar '16

19 Mar '16

Hello there, seems like the prop259 algorithm has kind of stabilized and you guys have jumped into implementation. That's great! A small problem in this process is that I'm probably the only person in Tor who understands the new algorithm right now. We could fix this by doing a small proposal IRC meeting where you guys could summarize the current state of the algorithm, as well as provide some simulation results. I think that folks like Nick, Mike and isis could provide valuable feedback at this point. Would you guys be interested in something like this? I'm fine with doing it next week at some point. Maybe Wednesday or Thursday? Maybe at 15:00 UTC? Let me know if that's convenient for you. Cheers!

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Introducing Snowflake (webrtc pt)
by Serene 18 Mar '16

18 Mar '16

Hi all, Snowflake is a webrtc pluggable transport inspired by flashproxy. (https://gitweb.torproject.org/pluggable-transports/snowflake.git) Arlo, David, and I have made lots of progress on it lately, and it now appears to have reached minimum viability. The following should result in a 100% bootstrap over WebRTC: ``` git clone https://git.torproject.org/pluggable-transports/snowflake.git cd snowflake/client go get go build tor -f torrc ``` In case you have a moment, it'd be cool if you tried it out and let us know whether it works for you. I'd really appreciate hearing about all the thoughts / concerns / issues before we move forward. -- More info -- Q: What are the benefits of this PT compared with other PTs? Snowflake combines the advantages of flashproxy and meek. Primarily: - It has the convenience of Meek, but can support magnitudes more users with negligible CDN costs. (Domain fronting only used for brief signalling / NAT-piercing to setup P2P webrtc which handles the actual traffic) - Arbitrarily high numbers of volunteer proxies are possible like in flashproxy, but NATs are no longer a usability barrier - no need for manual port forwarding! Q: How does it work? 1. Volunteers visit websites which host the "snowflake" proxy. (just like flashproxy) 2. Tor clients automatically find available browser proxies over the domain fronted signaling channel. 3. Tor client and browser proxy establish a WebRTC peer connection. 4. Proxy connects to some relay. 5. Tor occurs. Q: Why is it called Snowflake? There's a bunch of "ICE" negotiation happening for WebRTC, and it also involves a great abundance of ephemeral and short-lived (and special!) volunteer proxies... Anyhow, if Snowflake seems like it would be useful / desired here, it would be awesome if we had more help getting it stable, polished, audited, deployable, etc... Plenty of work to do! <3, ~serene P.S. Make sure you're using a recent version of Go (1.5+) P.P.S. The repo is available in these locations: - https://gitweb.torproject.org/pluggable-transports/snowflake.git - https://github.com/keroserene/snowflake

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[GSoC '16] Exitmap project - Introduction and request for comments
by Mridul Malpotra 18 Mar '16

18 Mar '16

Hi everyone! I'm Mridul. I wish to apply for the Exitmap improvements project mentored by Dr. Philipp Winter for the Google Summer of Code 2016. My current IRC handle is mtyamantau. Contents -------- 1. Introduction - About myself and experience with Tor 2. Exitmap - Current progress and questions 3. GSoC - Rough proposal structure and questions 1. Introduction - About myself and experience with Tor ------------------------------------------------------ I'm Mridul Malpotra, currently in my senior year pursuing bachelors in Computer Science from IIIT Delhi, India. My interests primarily lie in computer networks and network security, specifically anonymous networks like Tor and I2P. Through my now 1-year long undergraduate thesis work under Dr. Sambuddho Chakravarty, I have had exposure to the Tor network, relevant literature and some related projects, which helped me better understand and appreciate the current research and development going on. My work involved manually setting up testbeds through testing Tor networks on our institute intranet as well as on PlanetLab (for those wondering, I had recommended Chutney and Shadow). The current private testing Tor network is running on a PlanetLab slice (iiitd_mridul2) with ~170 nodes globally and 3 directory authorities. I used the control protocol through the Stem library to help in multiple circuit creation and stream attachments for measuring performance of a software over Tor. I have also had experience with open source software, by contributing to the Non intrusive load-monitoring toolkit (NILMTK) which is based on Python and Pandas. While working there, I helped contribute code for additional features, fixed a few bugs and also worked with a few of Python's package management and documentation systems. Relevant links: github.com/nilmtk/nilmtk/commits?author=mridulmalpotra 2. Exitmap - Current progress and questions ------------------------------------------- I recently read about Exitmap in the 'Differential Treatment of Anonymous Users' paper by Khattak et. al. The use case for fast automated scanning through Exitmap to evaluate ~1000 exit nodes was really interesting. On top of that, it fitted my use case of testing a particular software's performance over Tor. Familiarizing myself with the source code, I think I understand the basic layout for how the scanner works and appreciate the modularity of task executions. I followed the project's progress on github and have read the 'Spoiled Onions' paper by Winter et. al. In the coming 2 days, I plan to tinker around more with the code, discuss concerns, issues and/or suggestions if any, and get myself properly familiarized with the codebase. I also have certain ideas regarding what modules could be added and improvements made, some of which I have mentioned in the next section. I will also be reading the tech report on Exitmap and would be grateful if you can recommend any other resource(s) that I should be referring to. Lastly, I had a few queries related to the project and/or paper and apologize for the naivety in the questions if any. a. How was the bifurcation between stand-alone and same-process modules decided? Are there any advantages to allow for multiple forked processes for specific modules? b. For testing active attacks, can there be modules developed keeping other cleartext protocols like SNMP and Telnet in mind? Alternatively, is there a way to determine what protocols are being used over Tor and their popularity? c. How is Exitmap being crowdsourced currently? I'm interested to know how data is being collected from volunteers running the scanner. 3. GSoC - Rough proposal structure and questions ------------------------------------------------ Here I am listing the possible objectives that my project will be focusing on. I request your feedback and comments on the chosen topics and their descriptions. 1. Achieve autonomous scanning in Exitmap with periodic scans that, based on a certain algorithm, fetches relay descriptors and automates various subtasks for consistent data collection and verification. The main challenges that I expect will be intelligently recognizing which tasks to automate and when, and making the entire background process execution efficient in resource consumption. 2. Emulating multiple user interaction in individual modules and in Exitmap overall to provide indistinguishability to Exitmap from regular users. I will try to explore libraries for this purpose like Splinter with Selenium or BeautifulSoup with Requests that help dynamically interaction with the web resource. The main challenges that I expect will be to scale this automated testing alongside the running asynchronous jobs and making the entire scans look like genuine user interactions. Any suggestions on better ways to do this will be helpful. 3. Making the codebase more robust by adding unit test cases. I plan on using either the plain unittest/unittest2 framework or nose/nose2/pytest tools or any other alternatives that I may find or be recommended. I plan to simultaneously write the unit test cases for new code added and improve upon the exiting testing programs. 4. (Optional) I read from the mail threads on the tor-dev mailing list that the code needs to be converted to be Python3 compatible. Would like your opinion on whether it is a viable option and if it is possible, would like to include this in my list of tasks. 5. (Optional) If I can spare time in the milestone timeline and if discussion leads to some clarity, I would like to add another module for more cleartext protocols that could be implemented like SNMP or Telnet. I am also looking at possible local to remote attacks that are active at the application layer and could be tested in Exitmap. I'll update if I find anything. Next, I am drafting a week-wise timeline of what I plan to do over the duration of ~3 months. I will be dividing task 1 and 2 before and after the mid-term, with the optional tasks done in either of the slots and testing done alongside for everything. This is to ensure incremental milestones that can be useful to the community as I develop. Also, as I gain clarity on my objectives, I plan to refine this timeline to a week-wise format with buffers placed accordingly and present it in 2 days time. Lastly, I would appreciate any suggestions, criticism or feedback on this proposal regarding content, volume or specificities. I am looking forward to contributing to the Tor Project organization and interacting with developers here. Thanking you, (long mail I know, sorry) Sincerely, -- Mridul Malpotra Undergrad @ IIIT-Delhi <https://www.iiitd.ac.in/> mridulmalpotra.github.io ============================= PGP keyID: 0xb716e33ab6d0a653 <http://pgp.mit.edu/pks/lookup?op=get&search=0xb716e33ab6d0a653>

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"Not our bug" bugs
by Griffin Boyce 18 Mar '16

18 Mar '16

Hey all, There have been quite a few bug reports that discuss incompatibility with various Firefox extensions and with websites. In most cases, I can't replicate these bugs -- either because the extension in question has been patched, the website reported no longer exists, or the issue can't be replicated (which could be due to site updates and past Firefox incompatibility). Occasionally, the issue is real and still in effect, but isn't really a Tor bug (such as #7279, where a forum restricts logins by Tor users). We've all worked very hard to reduce overly-restrictive blacklist policies, but can't be everything for everyone. In these cases, I'd propose rejecting these bugs as either invalid or `not a bug`. These are all varying degrees of "not our bug" or "actually not a bug at all." Open to more thoughts on this. ~Griffin

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Notes from the prop267 meeting 2016-03-17
by Linus Nordberg 18 Mar '16

18 Mar '16

Hi, Here's a summary of what happened in the prop267 meeting in #tor-dev yesterday with Nick, Tom, Sebastian and myself. Sebastian started by summarising the proposal nicely. Topics discussed: - for bootstrap reasons we can't mandate using tor for all communication - SCT's or not: using SCT's instead of inclusion proofs would lower the burden on operating a log and save bytes on the wire - pushback on suggestion of turning all relays into auditors, reason being increased (code) complexity - there are some differences between "MITM:ing tor" and "MITM:ing on the internet", one being that a tor mitm is the controlling of a majority of the dirauth keys, which in many cases is more persistent than an IP layer MITM - the "eventually you escape a MITM" hand waving is problematic - we need a story on how a perfectly tor-MITM:ed TAILS user get back to the real network - relays and clients must check consensus documents the same way - hard fail or not when consensus isn't shown to be in a log? - handling of changes in the set of dirauths Identified next steps: - add text about what needs to be and what should be anonymised, taking bootstrapping issues into account - decide on replacing SHA2-256 with SHA3-512 or SHA2-512||SHA3-512 (taking availability of implementations into account) - decide on using SCT's or not - analyse the "TAILS user under MITM" case - analyse "set of dirauths changing" What did I miss? Full logs can be found at http://meetbot.debian.net/tor-dev/2016/tor-dev.2016-03-17-14.58.log.html

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What does TorBulkExitList.py return?
by Linus Nordberg 17 Mar '16

17 Mar '16

Hi, I'm trying to figure out why a list from [TorBulkExitList.py] is so much larger than what is seen in [exit-addresses]. Point in case: Earlier today the list from TorBulkExitList.py contained 58% more addresses than exit-addresses: --8<---------------cut here---------------start------------->8--- $ curl-tor -q 'https://check.torproject.org/cgi-bin/TorBulkExitList.py?ip=8.8.8.8' | egrep -v ^# | wc -l 1554 $ curl-tor -q https://check.torproject.org/exit-addresses | egrep ^ExitNode | wc -l 985 --8<---------------cut here---------------end--------------->8--- Counting relays with the Exit flag in a consensus of roughly the same time gives 912: --8<---------------cut here---------------start------------->8--- $ curl-tor -q http://171.25.193.9:443/tor/status-vote/current/consensus | egrep '^s.*Exit' | wc -l 912 --8<---------------cut here---------------end--------------->8--- If I read the code [check.py][exitips.py] correctly, we include the following IP addresses in what is served from [TorBulkExitList.py]: - all routers in the current consensus - with exit addresses from TorDNSEL file(s) added - for which stem's exit_policy.is_exiting_allowed() returns true I haven't read any TorDNSEL code and don't know exactly what above mentioned TorDNSEL file(s) are but I think they include results from active testing of what address exit relays really use for exiting. [exit-addresses] seems to be from TorDNSEL too but holding more of a snapshot while the files mentioned above supposedly cover some period of time. Before I dig further, perhaps someone here already know why the numbers differ so? I wouldn't expect the churn of addresses used for exiting to be high enough to explain the difference. [TorBulkExitList.py] https://check.torproject.org/cgi-bin/TorBulkExitList.py?ip=8.8.8.8 [exit-addresses] https://check.torproject.org/exit-addresses [check.go] https://gitweb.torproject.org/check.git/tree/check.go [exitips.py] https://gitweb.torproject.org/check.git/tree/scripts/exitips.py Thanks, Linus

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Revisiting prop224 cells
by George Kadianakis 16 Mar '16

16 Mar '16

Hello, I took a look at proposal 224 again, with the aim of revisiting the cell logic and format. Here are some matters that require discussion: 1) Should we keep backwards compability with old introduction and rendezvous points? Currently, proposal 224 actually tries to maintain backwards compatbility but at the cost of complicating the design. Specifically, to achieve backwards compatibility we need at least the following functionality: - Hidden services need to generate and publish an extra encryption key for each legacy introduction point (legacy enc-key). - Hidden services need a new cell subtype to register themselves to legacy introduction points (LEGACY_EST_INTRO). - Clients need a new cell to introduce themselves through legacy introduction points (LEGACY-INTRODUCE1) The above features are not extremely hard to implement, but because of their hacky backwards-compatible nature they do complicate the protocol and the code. Also, at some point when the network has upgraded we will have to rip this code off our codebase, otherwise it will just rot there. Also also, we will have to write non-trivial chutney tests to ensure the correctness of the backwards compatibility logic. Alternatively, we could choose to completely drop backwards compatibility with old introduction and rendezvous points. This means, that we will have to wait till a good part of the network has upgraded before we enable prop224 support for clients and services. This means that we will probably have to wait a whole release cycle (till the relay-side prop224 code becomes stable; is that 6 months?) before we can globally enable the client/HS prop224 functionality (although we can use the network ourselves for testing prop224 till then). What do you people think we should do here? Paradoxically, I'm currently thinking of _keeping_ the backwards compatibility design. Looking at the spec it seems like a medium difficulty engineering issue for us (maybe an 8% of the total prop224 task size), which sucks, but at least we don't have to worry about doing proper incremental deployment of prop224 on the network and worrying about release cycles. Also, as we move towards implementing prop224 cells, we can reevaluate our position here. I'm not confident about my position here, so feedback would be helpful. 2) I'd like to simplify the ESTABLISH_INTRO logic. Currently, ESTABLISH_INTRO seems like a needlessly _complex_ cell that is also _incomplete_. It's _complex_ because it takes 3 different forms depending on the value of its first byte. This complexity is caused partially by our backwards compability needs (see above), but also because we tried to cram the MAINT_INTRO message into this cell. It's _incomplete_ because it does not actually contain the "introduction point encryption key", so hidden services are forced to send the encryption key right after the initial ESTABLISH_INTRO cell using a second ESTABLISH_INTRO cell that is actually a MAINT_INTRO/UPDATE-KEYS-SUBCMD message. I have two suggestions here: * Let's include the intro point encryption key in the ESTABLISH_INTRO cell, so that hidden services can establish intro with a single cell (not for performance, but for simplicity). * Let's introduce a new cell type for MAINT_INTRO instead of cramming it into ESTABLISH_INTRO. Or at least, let's make it an extension of ESTABLISH_INTRO instead of using the first byte of the cell to get the cell subtype. What do you think? Also, this brings me to the next topic which is: 3) What is UPDATE-KEYS-SUBCMD good for? And why do intro points need to know the intro point encryption key? UPDATE-KEYS-SUBCMD seems to be the only use of MAINT_INTRO currently. It seems to be able to update the encryption keys of an introduction point circuit on the fly. But why does the introduction point need to know the encryption key in the first place? That key is only used by clients and hidden services to encrypt stuff end-to-end to each other. After discussing with dgoulet, the only reason I can think of is that so that the IP is aware of the encryption key, and if an incoming client Alice does not know the correct encryption key, then the IP can send it to her using an INTRODUCE_ACK message with [00 02] (and then Alice does not need to refetch the descriptor). But why would a client know the authentication key but not the encryption key? Do they have different rotation times? Why would the encryption key rotate before the authentication key? Maybe all these things are not necessary for now and we can just ditch UPDATE-KEYS-SUBCMD completely, assuming that both of those keys have the same rotation lifetime? And maybe even the IP does not need to know the encryption key at all? Am I missing something? Cheers!

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tor-dev March 2016