tor-dev December 2016

tor-dev@lists.torproject.org

25 participants
23 discussions

non-anonymous ephemeral onion services with stem
by Micah Lee 30 Jan '18

30 Jan '18

The stem documentation for create_ephemeral_hidden_service [1] says: "Changed in version 1.5.0: Added support for non-anonymous services." But I can't figure out to actually use this feature. There doesn't seem to be a new argument to say if you want your onion service to be non-anonymous. It also says, "Changed in version 1.5.0: Added the basic_auth argument." But there's a new basic_auth argument you can pass into the function to use that. [1] https://stem.torproject.org/api/control.html#stem.control.Controller.create…

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Proposal 247 (Hidden Service Vanguards) Overhaul
by Mike Perry 09 Jun '17

09 Jun '17

I spent some time trying to clean up proposal 247 based on everyone's comments, as well as based on my own thoughts. Please have a look if you commented on the original proposal, and complain if I've not taken your thoughts into account. (Aaron: In particular, I made several tradeoffs in favor of performance and DoS resistance that may be at odds with some of your suggestions, but I think the end result is still OK after looking into the Sybil rates and thinking about the adversary model in more detail. You may disagree). I've attached my updated version of the proposal inline in this mail, but the canonical updated proposal is in my remote at: https://gitweb.torproject.org/user/mikeperry/torspec.git/tree/proposals/247… Here's a summary of the changes (which are also listed in Git): * Try to make a coherent threat model and specify its assumptions * Fold in my comments about using disjoint sets ("buckets") for the third level guard. * Make the parameter discussion subsection its own section, and include tables with far more detail for the Sybil success rates. * Put the rotation period in a separate subsection from the number of guards * Switch to using min(X,X) and max(X,X) for the distribution for the second and third layer guard lifespans, respectively. Add a subsection describing this distribution (3.2.3) * Changed the default parameters based on these tables, and based on my own intuition about Tor's performance properties. * Move the load balancing, torrc, and other performance considerations to their own section (Section 5). * Move "3.2. Distinguishing new HS circuits from normal HS circuits" to section 4.1. * Fold in some of "3.3. Circuit nodes can now be linked to specific hidden services" into 4.1. Some of it I just removed, though, because I did not find it credible. * Added Roger's concerns about guard linkability to Section 4.2. * Added a denial of service subsection to Section 4.3. ================================ Filename: 247-hs-guard-discovery.txt Title: Defending Against Guard Discovery Attacks using Vanguards Author: George Kadianakis Created: 2015-07-10 Status: Draft 0. Motivation A guard discovery attack allow attackers to determine the guard node of a Tor client. The hidden service rendezvous protocol provides an attack vector for a guard discovery attack since anyone can force an HS to construct a 3-hop circuit to a relay (#9001). Following the guard discovery attack with a compromise and/or coercion of the guard node can lead to the deanonymization of a hidden service. 1. Overview This document tries to make the above guard discovery + compromise attack harder to launch. It introduces an optional configuration option which makes the hidden service also pin the second and third hops of its circuits for a longer duration. With this new path selection, we force the adversary to perform a Sybil attack and two compromise attacks before succeeding. This is an improvement over the current state where the Sybil attack is trivial to pull off, and only a single compromise attack is required. With this new path selection, an attacker is forced to do a one or more node compromise attacks before learning the guard node of a hidden service. This increases the uncertainty of the attacker, since compromise attacks are costly and potentially detectable, so an attacker will have to think twice before beginning a chain of node compromise attacks that he might not be able to complete. 1.1. Visuals Here is how a hidden service rendezvous circuit currently looks like: -> middle_1 -> middle_A -> middle_2 -> middle_B -> middle_3 -> middle_C -> middle_4 -> middle_D HS -> guard -> middle_5 -> middle_E -> Rendezvous Point -> middle_6 -> middle_F -> middle_7 -> middle_G -> middle_8 -> middle_H -> ... -> ... -> middle_n -> middle_n this proposal pins the two middles nodes to a much more restricted set, as follows: -> guard_3A_A -> guard_2_A -> guard_3A_B -> guard_3A_C -> Rendezvous Point HS -> guard_1 -> guard_3B_D -> guard_2_B -> guard_3B_E -> guard_3B_F -> Rendezvous Point Note that the third level guards are partitioned into buckets such that they are only used with one specific second-level guard. In this way, we ensure that even if an adversary is able to execute a Sybil attack against the third layer, they only get to learn one of the second-layer Guards, and not all of them. This prevents the adversary from gaining the ability to take their pick of the weakest of the second-level guards for further attack. 2. Design This feature requires the HiddenServiceGuardDiscovery torrc option to be enabled. When a hidden service picks its guard nodes, it also picks two additional sets of middle nodes `second_guard_set` and `third_guard_set` of size NUM_SECOND_GUARDS and NUM_THIRD_GUARDS respectively for each hidden service. These sets are unique to each hidden service created by a single Tor client, and must be kept separate and distinct. When a hidden service needs to establish a circuit to an HSDir, introduction point or a rendezvous point, it uses nodes from `second_guard_set` as the second hop of the circuit and nodes from that second hop's corresponding `third_guard_set` as third hops of the circuit. A hidden service rotates nodes from the 'second_guard_set' at a random time between MIN_SECOND_GUARD_LIFETIME hours and MAX_SECOND_GUARD_LIFETIME hours. A hidden service rotates nodes from the 'third_guard_set' at a random time between MIN_THIRD_GUARD_LIFETIME and MAX_THIRD_GUARD_LIFETIME hours. These extra guard nodes should be picked with the same path selection procedure that is used for regular middle nodes (though see Section 5.1 for performance reasons to restrict this slightly). Each node's rotation time is tracked independently, to avoid disclosing the rotation times of the primary and second-level guards. XXX how should proposal 241 ("Resisting guard-turnover attacks") be applied here? 2.1. Security parameters We set NUM_SECOND_GUARDS to 4 nodes and NUM_THIRD_GUARDS to 16 nodes (ie four sets of four). XXX: 3 and 12 might be another option here, in which case our rotation period for the second guard position can be reduced to 15 days. We set MIN_SECOND_GUARD_LIFETIME to 1 day, and MAX_SECOND_GUARD_LIFETIME to 33 days, for an average rotation rate of ~11 days, using the min(X,X) distribution specified in Section 3.2.2. We set MIN_THIRD_GUARD_LIFETIME to 1 hour, and MAX_THIRD_GUARD_LIFETIME to 18 hours, for an average rotation rate of ~12 hours, using the max(X,X) distribution specified in Section 3.2.2. XXX make all the above consensus parameters? Yes. Very yes, especially if we decide to change the primary guard lifespan. See Section 3 for more analysis on these constants. 3. Rationale and Security Parameter Selection 3.1. Threat model, Assumptions, and Goals Consider an adversary with the following powers: - Can launch a Sybil guard discovery attack against any node of a rendezvous circuit. The slower the rotation period of the node, the longer the attack takes. Similarly, the higher the percentage of the network is compromised, the faster the attack runs. - Can compromise any node on the network, but this compromise takes time and potentially even coercive action, and also carries risk of discovery. We also make the following assumptions about the types of attacks: 1. A Sybil attack is noisy. It will require either large amounts of traffic, multiple test circuits, or both. 2. A Sybil attack against the second or first layer Guards will be more noisy than a Sybil attack against the third layer guard, since the second and first layer Sybil attack requires a timing side channel in order to determine success, where as the Sybil success is almost immediately obvious to third layer guard, since it will now be returned as a rend point for circuits for the hidden service in question. 3. As soon as the adversary is confident they have won the Sybil attack, an even more aggressive circuit building attack will allow them to determine the next node very fast (an hour or less). 4. The adversary is strongly disincentivized from compromising nodes that may prove useless, as node compromise is even more risky for the adversary than a Sybil attack in terms of being noticed. Given this threat model, our security parameters were selected so that the first two layers of guards should be hard to attack using a Sybil guard discovery attack and hence require a node compromise attack. Ideally, we want the node compromise attacks to carry a non-negligible probability of being useless to the adversary by the time they complete. On the other hand, the outermost layer of guards should rotate fast enough to _require_ a Sybil attack. 3.2. Parameter Tuning 3.2.1. Sybil rotation counts for a given number of Guards The probability of Sybil success for Guard discovery can be modeled as the probability of choosing 1 or more malicious middle nodes for a sensitive circuit over some period of time. P(At least 1 bad middle) = 1 - P(All Good Middles) = 1 - P(One Good middle)^(num_middles) = 1 - (1 - c/n)^(num_middles) c/n is the adversary compromise percentage In the case of Vanguards, num_middles is the number of Guards you rotate through in a given time period. This is a function of the number of vanguards in that position (v), as well as the number of rotations (r). P(At least one bad middle) = 1 - (1 - c/n)^(v*r) Here's detailed tables in terms of the number of rotations required for a given Sybil success rate for certain number of guards. 1.0% Network Compromise: Sybil Success One Two Three Four Five Six Eight Nine Ten Twelve Sixteen 10% 11 6 4 3 3 2 2 2 2 1 1 15% 17 9 6 5 4 3 3 2 2 2 2 25% 29 15 10 8 6 5 4 4 3 3 2 50% 69 35 23 18 14 12 9 8 7 6 5 60% 92 46 31 23 19 16 12 11 10 8 6 75% 138 69 46 35 28 23 18 16 14 12 9 85% 189 95 63 48 38 32 24 21 19 16 12 90% 230 115 77 58 46 39 29 26 23 20 15 95% 299 150 100 75 60 50 38 34 30 25 19 99% 459 230 153 115 92 77 58 51 46 39 29 5.0% Network Compromise: Sybil Success One Two Three Four Five Six Eight Nine Ten Twelve Sixteen 10% 3 2 1 1 1 1 1 1 1 1 1 15% 4 2 2 1 1 1 1 1 1 1 1 25% 6 3 2 2 2 1 1 1 1 1 1 50% 14 7 5 4 3 3 2 2 2 2 1 60% 18 9 6 5 4 3 3 2 2 2 2 75% 28 14 10 7 6 5 4 4 3 3 2 85% 37 19 13 10 8 7 5 5 4 4 3 90% 45 23 15 12 9 8 6 5 5 4 3 95% 59 30 20 15 12 10 8 7 6 5 4 99% 90 45 30 23 18 15 12 10 9 8 6 10.0% Network Compromise: Sybil Success One Two Three Four Five Six Eight Nine Ten Twelve Sixteen 10% 2 1 1 1 1 1 1 1 1 1 1 15% 2 1 1 1 1 1 1 1 1 1 1 25% 3 2 1 1 1 1 1 1 1 1 1 50% 7 4 3 2 2 2 1 1 1 1 1 60% 9 5 3 3 2 2 2 1 1 1 1 75% 14 7 5 4 3 3 2 2 2 2 1 85% 19 10 7 5 4 4 3 3 2 2 2 90% 22 11 8 6 5 4 3 3 3 2 2 95% 29 15 10 8 6 5 4 4 3 3 2 99% 44 22 15 11 9 8 6 5 5 4 3 The rotation counts in these tables were generated with: def count_rotations(c, v, success): r = 0 while 1-math.pow((1-c), v*r) < success: r += 1 return r 3.2.2. Rotation Period As specified in Section 3.1, the primary driving force for the third layer selection was to ensure that these nodes rotate fast enough that it is not worth trying to compromise them, because it is unlikely for compromise to succeed and yield useful information before the nodes stop being used. For this reason we chose 1 to 18 hours, with a weighted distribution (Section 3.2.3) causing the expected average to be 12 hours. From the table in Section 3.2.1, it can be seen that this means that the Sybil attack will complete with near-certainty (99%) in 29*12 hours (14.5 days) for the 1% adversary, 3 days for the 5% adversary, and 1.5 days for the 10% adversary. Since rotation of each node happens independently, the distribution of when the adversary expects to win this Sybil attack in order to discover the next node up is uniform. This means that on average, the adversary should expect that half of the rotation period of the next node is already over by the time that they win the Sybil. With this fact, we choose our range and distribution for the second layer rotation to be short enough to cause the adversary to risk compromising nodes that are useless, yet long enough to require a Sybil attack to be noticeable in terms of client activity. For this reason, we choose a minimum second-layer guard lifetime of 1 day, since this gives the adversary a minimum expected value of 12 hours for during which they can compromise a guard before it might be rotated. If the total expected rotation rate is 11 days, then the adversary can expect overall to have 5.5 days remaining after completing their Sybil attack before a second-layer guard rotates away. 3.2.3. Rotation distribution In order to skew the distribution of the third layer guard towards higher values, we use max(X,X) for the distribution, where X is a random variable that takes on values from the uniform distribution. In order to skew the distribution of the second layer guard towards low values (to increase the risk of compromising useless nodes) we skew the distribution towards lower values, using min(X,X). Here's a table of expectation (arithmetic means) for relevant ranges of X (sampled from 0..N). The current choice for second-layer guards is noted with **, and the current choice for third-layer guards is noted with ***. Range Min(X,X) Max(X,X) 10 2.85 6.15 11 3.18 6.82 12 3.51 7.49 13 3.85 8.15 14 4.18 8.82 15 4.51 9.49 16 4.84 10.16 17 5.18 10.82*** 18 5.51 11.49 19 5.84 12.16 20 6.18 12.82 21 6.51 13.49 22 6.84 14.16 23 7.17 14.83 24 7.51 15.49 25 7.84 16.16 26 8.17 16.83 27 8.51 17.49 28 8.84 18.16 29 9.17 18.83 30 9.51 19.49 31 9.84 20.16 32 10.17** 20.83 33 10.51 21.49 34 10.84 22.16 35 11.17 22.83 36 11.50 23.50 37 11.84 24.16 38 12.17 24.83 39 12.50 25.50 4. Security concerns and mitigations 4.1. Mitigating fingerprinting of new HS circuits By pinning the middle nodes of rendezvous circuits, we make it easier for all hops of the circuit to detect that they are part of a special hidden service circuit with varying degrees of certainty. The Guard node is able to recognize a Vanguard client with a high degree of certainty because it will observe a client IP creating the overwhelming majority of its circuits to just a few middle nodes in any given 10-18 day time period. The middle nodes will be able to tell with a variable certainty that depends on both its traffic volume and upon the popularity of the service, because they will see a large number of circuits that tend to pick the same Guard and Exit. The final nodes will be able to tell with a similar level certainty that depends on their capacity and the service popularity, because they will see a lot of rend handshakes that all tend to have the same second hop. The most serious of these is the Guard fingerprinting issue. When proposal xxx-padding-negotiation is implemented, services that enable this feature should use those padding primitives to create fake circuits to random middle nodes that are not their guards, in an attempt to look more like a client. Additionally, if Tor Browser implements "virtual circuits" based on SOCKS username+password isolation in order to enforce the re-use of paths when SOCKS username+passwords are re-used, then the number of middle nodes in use during a typical user's browsing session will be proportional to the number of sites they are viewing at any one time. This is likely to be much lower than one new middle node every ten minutes, and for some users, may be close to the number of Vanguards we're considering. This same reasoning is also an argument for increasing the number of second-level guards beyond just two, as it will spread the hidden service's traffic over a wider set of middle nodes, making it both easier to cover, and behave closer to a client using SOCKS virtual circuit isolation. 4.2. Hidden service linkability Multiple hidden services on the same Tor instance should use separate second and third level guard sets, otherwise an adversary is trivially able to determine that the two hidden services are co-located by inspecting their current chosen rend point nodes. Unfortunately, if the adversary is still able to determine that two or more hidden services are run on the same Tor instance through some other means, then they are able to take advantage of this fact to execute a Sybil attack more effectively, since there will now be an extra set of guard nodes for each hidden service in use. For this reason, if Vanguards are enabled, and more than one hidden service is configured, the user should be advised to ensure that they do not accidentally leak that the two hidden services are from the same Tor instance. 4.3. Denial of service Since it will be fairly trivial for the adversary to enumerate the current set of rend nodes for a hidden service, denial of service becomes a serious risk for Vanguard users. For this reason, it is important to support a large number of third-level guards, to increase the amount of resources required to bring a hidden service offline by DoSing just a few Tor nodes. 5. Performance considerations The switch to a restricted set of nodes will very likely cause significant performance issues, especially for high-traffic hidden services. If any of the nodes they select happen to be temporarily overloaded, performance will suffer dramatically until the next rotation period. 5.1. Load Balancing Since the second and third level "guards" are chosen from the set of all nodes eligible for use in the "middle" hop (as per hidden services today), this proposal should not significantly affect the long-term load on various classes of the Tor network, and should not require any changes to either the node weight equations, or the bandwidth authorities. Unfortunately, transient load is another matter, as mentioned previously. It is very likely that this scheme will increase instances of transient overload at nodes selected by high-traffic hidden services. One option to reduce the impact of this transient overload is to restrict the set of middle nodes that we chose from to some percentage of the fastest middle-capable relays in the network. This may have some impact on load balancing, but since the total volume of hidden service traffic is low, it may be unlikely to matter. 5.2. Circuit build timeout The adaptive circuit build timeout mechanism in Tor is what corrects for instances of transient node overload right now. The timeout will naturally tend to select the current fastest and least-loaded paths even through this set of restricted routes, but it may fail to behave correctly if there are a very small set of nodes in each guard set, as it is based upon assumptions about the current path selection algorithm, and it may need to be tuned specifically for Vanguards, especially if the set of possible routes is small. 5.3. OnionBalance At first glance, it seems that this scheme makes multi-homed hidden services such as OnionBalance[1] even more important for high-traffic hidden services. Unfortunately, if it is equally damaging to the user for any of their multi-homed hidden service locations to be discovered, then OnionBalance is strictly equivalent to simply increasing the number of second-level guard nodes in use, because an active adversary can perform simultaneous Sybil attacks against all of the rend points offered by the multi-homed OnionBalance introduction points. 5.4. Default vs optional behavior We suggest this torrc option to be optional because it changes path selection in a way that may seriously impact hidden service performance, especially for high traffic services that happen to pick slow guard nodes. However, by having this setting be disabled by default, we make hidden services who use it stand out a lot. For this reason, we should in fact enable this feature globally, but only after we verify its viability for high-traffic hidden services, and ensure that it is free of second-order load balancing effects. Even after that point, until Single Onion Services are implemented, there will likely still be classes of very high traffic hidden services for whom some degree of location anonymity is desired, but for which performance is much more important than the benefit of Vanguards, so there should always remain a way to turn this option off. 6. Future directions Here are some more ideas for improvements that should be done sooner or later: - Maybe we should make the size and rotation period of secondary/third guard sets to be configurable by the user. - To make it harder for an adversary, a hidden service MAY extend the path length of its circuits by an additional static hop. This forces the adversary to use another coercion attack to walk the chain up to the hidden service. 7. Acknowledgments Thanks to Aaron Johnson, John Brooks, Mike Perry and everyone else who helped with this idea. 1. https://onionbalance.readthedocs.org/en/latest/design.html#overview -- Mike Perry

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Re: [tor-dev] Flashproxy has been Deactivated by Stanford? Why?
by David Fifield 12 Mar '17

12 Mar '17

On Tue, Dec 20, 2016 at 01:21:04AM +0800, tomli(a)riseup.net wrote: > It turned out that the entire code has been commented out and apparently > Flashproxy became > out of service. Why? Has the project discontinued, or just down for > maintenance? Flash proxy is basically retired now. It was removed from Tor Browser a year ago (https://bugs.torproject.org/17428) after it had been supplanted by more effective transports. I don't know why there was a blog post on December 16 promoting flash proxy, because it's no longer used. Even when flash proxy was part of Tor Browser, it had very few users (less than 100; see https://metrics.torproject.org/userstats-bridge-transport.html?start=2013-0…), probably because of the difficulty of running it as a client (https://trac.torproject.org/projects/tor/wiki/doc/PluggableTransports/Flash…). Compare those user numbers to meek (current about 10K) or obfs4 (30K). The reason I haven't asked people to stop running the flash proxy badge is we're working on a new pluggable transport along the same lines but without the usability challenges: https://trac.torproject.org/projects/tor/wiki/doc/Snowflake. I was thinking about adapting existing flash proxy badges to provide capacity to Snowflake instead. This would go for Cupcake as well. The need to get the badge running again hasn't been pressing because Snowflake isn't deployed yet, but we're getting close. The badge was deactivated by Stanford (without my knowledge, but I found out a while ago). I arranged with them to move it to alternate hosting and have them install a redirect, but that has been a low priority behind other work on Snowflake. I'm sorry about the confusion. If I get some time I'll add a notice to the flash proxy main page saying that it's been retired.

2 2

onionoo.tpo stuck at 2016-05-13 12:00
by nusenu 29 Jan '17

29 Jan '17

Hi Karsten, I was surprised that ornetradar did not send a single email for yesterday's new relays. After looking into it, it turned out it is an onionoo problem. "relays_published":"2016-05-13 12:00:00" https://onionoo.torproject.org/details?limit=4 regards, nusenu

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Proposal 274: A Name System API for Tor Onion Services
by George Kadianakis 26 Jan '17

26 Jan '17

Hello list, we've been busy discussing secure name systems for the past few months, and how we could integrate them with Tor. We had a few people ask us for precise interfaces, so here is an attempt for a modular name system API. It's largely based on the PT API, which has been pretty successful. The proposal was brainstormed on a Sunday morning in Seattle between Yawning, David and me. I wrote the actual proposal contents so any innacuracies, impossibilities and errors are mine :) If people like it and are interested in implementing it, we can draft out an implementation plan for any person who wants to go for it. But for now, please consider this proposal text as a draft that is meant to be improved from this list's feedback. Have fun and looking forward to your comments (and code). --- Filename: 274-naming-layer-api.txt Title: A Name System API for Tor Onion Services Author: George Kadianakis, Yawning Angel, David Goulet Created: 04-Oct-2016 Status: Draft Table Of Contents: 1. Introduction 1.1. Motivation 1.2. Design overview and rationale 2. System Specification 2.1. System overview [SYSTEMOVERVIEW] 2.2. System Illustration 2.3. System configuration [TORRC] 2.3.1. Tor name resolution logic 2.4. Name system initialization [INITPROTOCOL] 2.5. Name resolution using NS API 2.5.1. Message format 2.5.2. RESOLVED status codes 2.5.3. Further name resolution behavior 2.6. Cancelling a name resolution request 2.7. Launching name plugins [INITENVVARS] 2.8. Name plugin workflow [NSBEHAVIOR] 2.8.1. Name plugin shutdown [NSSHUTDOWN] 2.9. Further details of stdin/stdout communication 2.9.1. Message Format 3. Discussion 3.1. Using second-level domains instead of tld 3.2. Name plugins handling all tlds '*' 3.3. Deployment strategy 3.4. Miscellaneous discussion topics 4. Acknowledgements A.1: Example communication Tor <-> name plugin [PROTOEXAMPLE] A.2: Example plugins [PLUGINEXAMPLES] 1. Introduction This proposal specifies a modular API for integrating name systems with Tor. 1.1. Motivation Tor onion service addresses are decentralized and self-authenticated but they are not human-memorable (e.g. 3g2upl4pq6kufc4m.onion). This is a source of poor usability, since Internet users are familiar with the convenient naming of DNS and are not used to addresses being random text. In particular, onion addresses are currently composed of 16 random base32 characters, and they look like this: 3g2upl4pq6kufc4m.onion vwakviie2ienjx7t.onion idnxcnkne4qt76tg.onion vwakviie2ienjx6t.onion When Proposal 224 get deployed, onion addresses will become even bigger: 53 base32 characters. That's: llamanymityx4fi3l6x2gyzmtmgxjyqyorj9qsb5r543izcwymle.onion lfels7g3rbceenuuqmpsz45z3lswakqf56n5i3bvqhc22d5rrsza.onion odmmeotgcfx65l5hn6ejkaruvai222vs7o7tmtllszqk5xbysola.onion qw3yvgovok3dsarhqephpu2pkiwzjdk2fgdfwwf3tb3vgzxr5kba.onion Over the years Tor users have come up with various ad-hoc ways of handling onion addresses. For example people memorize them, or use third-party centralized directories, or just google them everytime. We believe that the UX problem of non-human-memorable problems is not actually solved with the above ad-hoc solutions and remains a critical usability barrier that prevents onion services from being used by a wider audience. 1.2. Design overview and rationale During the past years there has been lots of research on secure naming and various such systems have been proposed (e.g. GNS, Namecoin, etc.). Turns out securely naming things is a very hard research problem, and hence none of the proposed systems is a clear winner: all of them carry various trade-offs. Furthermore, none of the proposed systems has seen widespread use so far, which makes it even harder to pick a single project. Given the plenitude of options, one approach to decide which system is best is to make various decent name systems available and let the Tor community and the sands of time pick the winner. Also, it might be that there is no single winner, and perhaps different specialized name system should be used in different situations. We believe that by getting secure name systems actually get utilized by real users, the whole field will mature and existing systems will get battle-hardened. Hence, the contribution of this proposal is a modular Name System API (NSA) that allows developers to integrate their own name systems in Tor. The interface design is name-system-agnostic, and it's heavily based on the pluggable transports API (proposal 180). It should be flexible enough to accommodate all sorts of name systems (see [PLUGINEXAMPLES]). 2. System Specification A developer that wants to integrate a name system with Tor needs to first write a wrapper that understands the Tor Name System API (NS API). Using the Name System API, Tor asks the name system to perform name queries, and receives the query results. The NS API works using environment variables and stdin/stdout communication. It aims to be portable and easy to implement. 2.1. System overview [SYSTEMOVERVIEW] Here is an overview of the Tor name system: Alice, a Tor user, can activate various name systems by editing her torrc file and specifying which tld each name system is responsible for. For this section, let's consider a simple fictional name system, unicorn, which magically maps domains with the .corn tld to the correct onion address. Here it is: OnionNamePlugin 0 .corn /usr/local/bin/unicorn After Alice enables the unicorn plugin, she attempts connecting to elephantforum.corn. Tor will intercept the SOCKS request, and use the executable at /usr/local/bin/unicorn to query the unicorn name system for elephantforum.corn. Tor communicates with the unicorn plugin using the Tor NS API through which name queries and their results can be transported using stdin/stdout. If elephantforum.corn corresponds to an onion address in the unicorn name system, unicorn should return the onion address to Tor using the Tor NS API. Tor must then internally rewrite the elephantforum.corn address to the actual onion address, and initiate a connection to it. 2.2. System Illustration Here is a diagram illustrating how the Tor Name System API works. The name system used in this example is GNS, but there is nothing GNS-specific here and GNS could be swapped for any other name system (like hosts files, or Namecoin). The example below illustrates how a user who types debian.zkey in their Tor browser gets redirected to sejnfjrq6szgca7v.onion after Tor consults the GNS network. Please revisit this illustration after reading the rest of the proposal. | $~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~$ | 1. $ 4. GNS magic!! $ | User: SOCKS CONNECT to $ debian.zkey -> sejnfjrq6szgca7v.onion$ | http://debian.zkey/ $~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~$~~~~~~~$ | $ +-----|-----------------------------------------+ $ |+----v-----+ 2. +---------+| 3. $ ||Tor | debian.zkey |Tor || debian.zkey +-$-------+ ||Networking------------------------->Naming -------------------------> | ||Submodule | |Submodule|| Tor Name System API | GNS | || <------------------------- <------------------------- wrapper| || | 6. | ||5. | | |+----|-----+ sejnfjrq6szgca7v.onion +---------+|sejnfjrq6szgca7v.onion +---------+ +-----|-----------------------------------------+ | 7. | Tor: Connect to | http://sejnfjrq6szgca7v.onion/ v 2.3. System configuration [TORRC] As demonstrated in [SYSTEMOVERVIEW], a Tor user who wants to use a name system has to edit their configuration file appropriately. Here is the torrc line format: OnionNamePlugin <priority> <tld> <path> where <priority> is a positive integer denoting the priority with which this name plugin should be consulted. <tld> is a string which restricts the scope of this plugin to a particular tld. Finally, <path> is a filesystem path to an executable that speaks the Tor Name System API and can act as an intermediary between Tor and the name system. For example here is a snippet from a torrc file: OnionNamePlugin 0 .hosts /usr/local/bin/local-hosts-file OnionNamePlugin 1 .zkey /usr/local/bin/gns-tor-wrapper OnionNamePlugin 2 .bit /usr/local/bin/namecoin-tor-wrapper OnionNamePlugin 3 .scallion /usr/local/bin/community-hosts-file 2.3.1. Tor name resolution logic When Tor receives a SOCKS request to an address that has a name plugin assigned to it, it needs to perform a query for that address using that name plugin. If there are multiple name plugins that correspond to the requested address, Tor queries all relevant plugins sorted by their priority value, until one of them returns a successful result. If two plugins have the same priority value, Tor MUST abort. If all plugins fail to successfuly perform the name resolution, Tor SHOULD default to using the exit node for name resolution. XXX or not? because of leaks? 2.4. Name system initialization [INITPROTOCOL] When Tor finds OnionNamePlugin lines in torrc, it launches and initializes their respective executables. When launching name plugins, Tor sets various environment variables to pass data to the name plugin (e.g. NS API version, state directory, etc.). More information on the environment variables at [INITENVVARS]. After a name plugin initializes and parses all needed environment variables, it communicates with Tor using its stdin/stdout. The first line that a name plugin sends to stdout signifies that it's ready to receive name queries. This line looks like this: INIT <VERSION> <STATUS_CODE> [<STATUS_MSG>] where VERSION is the Tor NS API protocol version that the plugin supports, STATUS_CODE is an integer status code, and STATUS_MSG is an optional string error message. STATUS_CODE value 0 is reserved for "success", and all other integers are error codes. See [PROTOEXAMPLE] for an example of this protocol. 2.5. Name resolution using NS API Here is how actual name resolution requests are performed in NS API. 2.5.1. Message format When Tor receives a SOCKS request to an address with a tld that has a name plugin assigned to it, Tor performs an NS API name query for that address. Tor does this by printing lines on the name plugin stdout as follows: RESOLVE <QUERY_ID> <NAME_STRING> where QUERY_ID is a unique integer corresponding to this query, and NAME_STRING is the name to be queried. When the name plugin completes the name resolution, it prints the following line in its stdout: RESOLVED <QUERY_ID> <STATUS_CODE> <RESULT> where QUERY_ID is the corresponding query ID and STATUS_CODE is an integer status code. RESULT is the resolution result (an onion address) or an error message if the resolution was not succesful. See [PROTOEXAMPLE] for an example of this protocol. XXX Should <RESULT> be optional in the case of failure? 2.5.2. RESOLVED status codes Name plugins can deliver the following status codes: 0 -- The name resolution was successful. 1 -- Name resolution generic failure. 2 -- Name tld not recognized. 3 -- Name not registered. 4 -- Name resolution timeout exceeded. XXX add more status codes here as needed 2.5.3. Further name resolution behavior Tor and name plugins MAY cache name resolution results in memory as needed. Caching results on disk should be avoided. Tor SHOULD abort (or cancel) an ongoing name resolution request, if it takes more than NAME_RESOLUTION_TIMEOUT seconds. XXX NAME_RESOLUTION_TIMEOUT = ??? Tor MUST validate that the resolution result is a valid .onion name. XXX should we also accept IPs and regular domain results??? XXX perhaps we should make sure that results are not names that need additional name resolution to avoid endless loops. e.g. imagine some sort of loop like this: debian.zkey -> debian-bla.zkey -> debian.zkey -> etc. 2.6. Cancelling a name resolution request Tor might need to cancel an ongoing name resolution request (e.g. because a timeout passed, or the client is not interested in that address anymore). In this case, Tor sends the following line to the plugin stdout as follows: CANCEL <QUERY_ID> to which the name plugin, after performing the cancellation, SHOULD answer with: CANCELED <QUERY_ID> 2.7. Launching name plugins [INITENVVARS] As described in [INITPROTOCOL], when Tor launches a name plugin, it sets certain environment variables. At a minimum, it sets (in addition to the normal environment variables inherited from Tor): "TOR_NS_STATE_LOCATION" -- A filesystem directory path where the plugin should store state if it wants to. This directory is not required to exist, but the plugin SHOULD be able to create it if it doesn't. The plugin MUST NOT store state elsewhere. Example: TOR_NS_STATE_LOCATION=/var/lib/tor/ns_state/ "TOR_NS_PROTO_VERSION" -- To tell the plugin which versions of this configuration protocol Tor supports. Future versions will give a comma-separated list. Plugins MUST accept comma-separated lists containing any version that they recognize, and MUST work correctly even if some of the versions they don't recognize are non-numeric. Valid version characters are non-space, non-comma printing ASCII characters. Example: TOR_NS_PROTO_VERSION=1,1a,2,4B "TOR_NS_PLUGIN_OPTIONS" -- Specifies configuration options for this name plugin as a semicolon-separated list of k=v strings with options that are to be passed to the plugin. Colons, semicolons, equal signs and backslashes MUST be escaped with a backslash. If there are no arguments that need to be passed to any of the plugins, "TOR_NS_PLUGIN_OPTIONS" MAY be omitted. For example consider the following options for the "banana" name plugin: TOR_NS_PLUGIN_OPTIONS=timeout=5;url=https://bananacake.com Will pass to banana the parameters 'timeout=5' and 'url=https://bananacake.com'. XXX Do we like this option-passing interface? Do we have any lessons from our PT experiences? XXX Add ControlPort/SocksPort environment variables. See [PROTOEXAMPLE] for an example of this environment 2.8. Name plugin workflow [NSBEHAVIOR] Name plugins follow the following workflow: 1) Tor sets the required environment values and launches the name plugin as a sub-process (fork()/exec()). See [INITENVVARS]. 2) The name plugin checks its environment, and determines the supported NS API versions using the env variable TOR_NS_PROTO_VERSION. 2.1) If there are no compatible versions, the name plugin writes an INIT message with a failure status code as in [INITPROTOCOL], and then shuts down. 3) The name plugin parses and handles the rest of the environment values. 3.1) If the environment variables are malformed, or otherwise invalid, the name plugin writes an INIT message with a failure status code as in [INITPROTOCOL], and then shuts down. 4) After the name plugin completely initializes, it sends a successful INIT message to stdout as in [INITPROTOCOL]. Then it continues monitoring its stdin for incoming RESOLVE messages. 6) When the name plugin receives a RESOLVE message, it performs the name resolution and replies with the appropriate RESOLVED message. 7) Upon being signaled to terminate by the parent process [NSSHUTDOWN], the name plugin gracefully shuts down. 2.8.1. Name plugin shutdown [NSSHUTDOWN] To ensure clean shutdown of all name plugins when Tor shuts down, the following rules apply for name plugins: Name plugins MUST handle OS specific mechanisms to gracefully terminate (e.g. SIGTERM). Name plugins SHOULD monitor their stdin and exit gracefully when it is closed. 2.9. Further details of stdin/stdout communication 2.9.1. Message Format Tor communicates with its name plugins by writing NL-terminated lines to stdout. The line metaformat is <Line> ::= <Keyword> <OptArgs> <NL> <Keyword> ::= <KeywordChar> | <Keyword> <KeywordChar> <KeyWordChar> ::= <any US-ASCII alphanumeric, dash, and underscore> <OptArgs> ::= <Args>* <Args> ::= <SP> <ArgChar> | <Args> <ArgChar> <ArgChar> ::= <any US-ASCII character but NUL or NL> <SP> ::= <US-ASCII whitespace symbol (32)> <NL> ::= <US-ASCII newline (line feed) character (10)> Tor MUST ignore lines with keywords that it doesn't recognize. 3. Discussion 3.1. Using second-level domains instead of tld People have suggested that users should try to connect to reddit.zkey.onion instead of reddit.zkey. That is, we should always preserve .onion as the tld, and only utilize second-level domains for naming. The argument for this is that this way users cannot accidentally leak addresses to DNS, as the .onion domain is reserved by RFC 7686. The counter-argument here is that this might be confusing to users since they are not used to the second-level domain being special (e.g. co.uk). Also, what happens when someone registers a 16-character name, that matches the length of a vanilla onion address? We should consider the concerns here and take the right decision. 3.2. Name plugins handling all tlds '*' In [TORRC], we assigned a single tld to each name plugin. Should we also accept catch-all tlds using '*'? I'm afraid that this way a name system could try to resolve even normal domains like reddit.com . Perhaps we trust the name plugin itself, but maybe the name system network could exploit this? Also, the catch-all tld will probably cause some engineering complications in this proposal (as it did for PTs). 3.3. Deployment strategy We need to devise a deployment strategy that will allow us to improve the UX of our users as soon as possible, but without taking hasty, sloppy or uneducated decisions. For starters, we should make it easy for developers to write wrappers around their secure name systems. We should develop libraries that speak the NS API protocol and can be used to quickly write wrappers. Similar libraries were quite successful during pluggable transport deployment; see pyptlib and goptlib. In the beginning, name plugins should be third-party applications that can be installed by interested users manually or through package managers. Users will also have to add the appropriate OnionNamePlugin line to their torrc. This will be a testing phase, and also a community-growing phase. After some time, and when we get a better idea of how name plugins work for the community, we can start considering how to make them more easily usable. For example, we can start by including some name plugins into TBB in an optional opt-in fashion. We should be careful here, as people have real incentives for attacking name systems and we should not put our users unwillingly in danger. 3.4. Miscellaneous discussion topics 1. The PT spec tries hard so that a single executable can expose multiple PTs. In this spec, it's clear that each executable is a single name plugin. Is this OK or a bad idea? Should we change interfaces so that each name plugin has an identifier, and then use that identifier for things? 2. Should we make our initialization protocol _identical_ to the PT API initialization protocol? That is, use ENV-ERROR etc. instead of INT? 3. Does it make sense to support reverse queries, from .onion to names? So that people auto-learn the names of the onions they use? 4. Acknowledgements Proposal details discussed during Tor hackfest in Seattle between Yawning, David and me. Thanks to Lunar and indolering for more discussion and feedback. Appendix A.1: Example communication Tor <-> name plugin [PROTOEXAMPLE] Environemnt variables: TOR_NS_STATE_LOCATION=/var/lib/tor/ns_state TOR_NS_PROTO_VERSION=1 TOR_NS_PLUGIN_OPTIONS=timeout=5;cache=/home/user/name_cache Messages between Tor and the banana name plugin: Name plugin (banana) -> Tor: INIT 1 0 Tor -> Name plugin (banana): RESOLVE 1 daewonskate.banana Name plugin (banana) -> Tor: RESOLVED 1 0 jqkscnkne4qt91iq.onion Tor -> Name plugin (banana): RESOLVE 1 architecturedirect.zkey Name plugin (banana) -> Tor (banana): RESOLVE 1 2 "zkey not recognized tld" Tor -> Name plugin (banana): RESOLVE 1 origamihub.banana Name plugin (banana) -> Tor (banana): RESOLVE 1 2 wdxfpaxar4dg12vd.onion Appendix A.2: Example plugins [PLUGINEXAMPLES] Here are a few examples of name plugins for brainstorming: a) Simplest plugin: A local hosts file. Basically a local petname system that maps names to onion addresses. b) A remote hosts file. A centralized community hosts file that people trust. c) Multiple remote hosts files. People can add their own favorite community hosts file. d) Multiple remote hosts files with notaries and reputation trust. Like moxie's convergence tool but for names. e) GNS f) OnioNS g) Namecoin/Blockstart

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Remaining 4 bits in prop224 addresses
by Jesse V 06 Jan '17

06 Jan '17

Hello all, I've been closely following the other Proposal 224 threads regarding the next-generation of onion services. I'm glad to see that we have a timeline and plan for migrating the network. One unresolved point is what to do with the remaining 4 bits in the longer addresses. Section 1.2 in the 224 document states "Note that since master keys are 32 bytes long, and 52 bytes of base 32 encoding can hold 260 bits of information, we have four unused bits in each of these names." It seems a waste for these to be zeroed out. The four bits could also be used to hold client-side flags, but I'm not aware of any applicable client settings that could be used here. I suggest that we use them as a checksum. (wasn't this proposed in Arlington?) Since speed isn't a priority, aside from Adler-32 or some CRC function, we could also hash the 32-byte key and use the first four bits of the hash. I think a checksum is best because it helps ensure data integrity when the address is shared online, copy/pasted, or physically written down. Bitcoin addresses contain a checksum as well for exactly this reason. They use a combination of SHA-256 and RIPEMD-160 to compute the checksum component. Source: 1) https://en.bitcoin.it/wiki/Technical_background_of_version_1_Bitcoin_addres… 2) https://bitcoin.stackexchange.com/questions/32353/ What do we think about a checksum, or do we have other plans here? I ask because once we nail down the address format, I can add support for 224 into my Onion Name System. -- Jesse

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Interested in contributing to Tor Project - IP Hijacking detection for Tor relays
by Nikhil 29 Dec '16

29 Dec '16

Hi, I am Nikhil. R, a student from India. You can know more about me from here[1] and here[2]. I have been running a Tor relay for sometime and now I am interested in contributing to the Tor Project. Specifically, I would like to work on IP Hijacking detection for Tor relays. I understand this does not involve directly with the Tor core hence I think this project is ideal in getting my feet wet with the Tor Community and get me started for further contributions to the Tor Project. BGP hijacking is difficult without inside help from ISP's(I think ?) but state run adversaries don't necessarily have this problem. This has a great risk of exposing all Tor clients or even mess around with the name resolution in exit relays. I have also read about incidents where an attacker using BGP hijacking, hijacked a portion of a Bitcoin mining pool traffic to pay himself instead of the people contributing the processing power. I feel BGP has major security implications in this aspect and a monitoring service is necessary. There are many monitoring services and we can possibly leverage one of them for the routing data. The main motive of the service would be to find anomalies/ malicious changes in the routing information compared to previous snapshots of the same. How do we actually do this comparison ? Any pointers for that ? The project also mentions that the service should be Tor-aware. What exactly does this mean ? Does it mean that, it should monitor all tor relays ip addresses ? It would be wonderful if you could elaborate on the project in a little more detail. I am a beginner in this area and please excuse me if any of the above questions are too stupid. Regards, Nikhil. R [1]:https://in.linkedin.com/in/rnikhil275 [2]https://rnikhil275.github.io

1 0

Can I modify obfs4 proxy code for my purpose?
by trmobid＠tutanota.com 22 Dec '16

22 Dec '16

Hi. I have some questions about modifying codes. 1. I wanna build a password protected obfs4 proxy sever with my VPS. I don't need that much privacy in terms of MITM for this. I just wanna know if it is ok to build such server in Tor network. 2.I wanna overrides some Javascript API with add-on. but... I just tried this with latest Torbrowser. it seems like I can't overrides some API's. Because same add-on I made worked on normal Firefox browser. I wanna avoid some fingerprint tracking recently discovered. Is there any reason to block overrides by add-on? Or am I missing something? I wanna know which is best way to do this. add-on or Torbrowser itself. Thanks.

2 2

prop224: What should we do with torrc options?
by David Goulet 20 Dec '16

20 Dec '16

Hi everyone! We are soon at the stage of implementing the service part of proposal 224 (next gen. hidden service.). Parent ticket is #20657 but I'll be discussing here ticket #18054. In a nutshell, we need to figure out the interface for the torrc file[1]. We currently have some options to configure an hidden service and the question is now how do we proceed on using those for next version? Instead of listing all options and going in an endless loop of possibilities, I'll outline what we've discussed so far between some of us. In the following, "v2" is current hidden service and "v3" is the next generation detailed in prop224. 1) Once v3 is released, from that point on _no_ v2 service will be allowed to be created by "tor" itself. It will always be possible to do it by hand by creating an RSA key and putting it in the service directory (see 3 below). The reasoning for this is that we really want to phase out as quickly as possible the v2 protocol for privacy and security reasons. 2) All the current torrc options will be kept for v3 as they all apply in terms of format. (One exception might be the client authorization.) 3) When tor is loading config for a service: if a v2 key is found that is an RSA key, we treat that service as v2, print a deprecation warning and continue. if a v3 key is found, use v3, all is good. if no key is found, consider a new service and generate v3 (ties to 1 above). 4) Over time, extra option might appear and they will be ONLY for v3 unless for force majeur security madness. One of those options that we want to add is this one as offline key will be a reality with v3: "HiddenServiceOfflineKey 1" It will indicate tor to _not_ generate the master identity key and will require the user to put the public key in the HiddenServiceDir. Note that with all of the above it will be possible to have one of your application on both v2 and v3 address. Here is a snippet as an example: # v2 HiddenServiceDir /srv/hs/v2 HiddenServicePort 80 localhost:80 # v3 HiddenServiceDir /srv/hs/v3 HiddenServicePort 80 localhost:80 The important part here is the different directories but the port points to the same place. Ok here it is. Please comment, improve, or propose! :) Cheers! David [1] https://www.torproject.org/docs/tor-manual.html.en (see HIDDEN SERVICE OPTIONS)

10 42

automatically detect many new identical/similar bridges
by nusenu 16 Dec '16

16 Dec '16

Hi, in the context of [1] I'm wondering if it makes sense to add bridge support to ornetradar. If there is any value to automatically detect multiple new bridges: - Do bridges publish ContactInfo in their descriptor? If not: Why not? (it shouldn't disclose their bridge location) another raw idea: - would the bridge auth be willing to publish a randomly generated AS identifier (regenerated daily) that allows new bridges added on the same day to be grouped by that identifier without directly disclosing the AS itself. Note: This introduces a confirmation opportunity, where attackers can learn the AS in which a new bridge is added if they added a bridge in the same AS on the same day. To reduce this problem it could be a hourly generated identifier. regards, nusenu [1] https://lists.torproject.org/pipermail/tor-project/2016-December/000851.html

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tor-dev December 2016