tor-dev March 2017

tor-dev@lists.torproject.org

51 participants
41 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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Proposition: Applying an AONT to Prop224 addresses?
by Alec Muffett 15 Apr '17

15 Apr '17

Hi, So: a bunch of us were discussing Prop224 Onion addresses, and their UX-malleability. Specifically: that there are small bit fields in the current Prop224 Onion Address schema (eg: version, and other future structure?) which can be tweaked or amended without otherwise changing the functionality of the address, or without much changing what the user sees in the (say) browser address bar. This is a point of significant concern because of issues like phishing and passing-off - by analogy: t0rpr0ject.0rg versus torproject.org - and other games that can be played with a prop224 address now, or in future, to game user experience. We discussed the existing "hash the public key before base-32 encoding" approach, but hashing breaks the prop224 key blinding. Ian Goldberg - thank you Ian - offered this attractive solution: apply a *reversible* "All Or Nothing Transform" (AONT) to the entire Prop224 Onion Address, prior to Base32 Encoding. This way, even a single-bit mutation of (say) version number will have a "diffusion" effect, impacting ~ N/2 of the bits whilst having O(1) cost and being reversible so as not to impact the rest of Prop224. The result would be onion addresses which are less "tamperable" / more deterministic, that closer to one-and-only-one published onion address will correspond to an onion endpoint. What does the panel think? - alec -- http://dropsafe.crypticide.com/aboutalecm

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Interest in collaborating on a standard Ed25519 key blinding scheme?
by Tony Arcieri 15 Apr '17

15 Apr '17

I'm trying to gauge interest on the IRTF's CFRG mailing list regarding collaborating on a draft for a standard Ed25519 hierarchical derivation / key blinding scheme: https://mailarchive.ietf.org/arch/msg/cfrg/lM1ix9R-0tVzhZorQhQlKvi4wpA The post makes several mentions of Tor's work in the space in regard to the next-generation hidden services design. I think it'd be great if Tor were to collaborate on the design of such a scheme and adopt it for the new hidden services design. I see a lot of convergent evolution in this space and think it would be great if there were a single standard everyone could implement. Even if you don't, I think there are some ideas from similar schemes Tor should fold back into its own design, particularly in regard to how certain bits of the private scalar are "clamped". Some discussion of that here: https://moderncrypto.org/mail-archive/curves/2017/000862.html tl;dr: clamp the third highest bit of the root scalar to zero (in addition to the bits normally clamped in the non-canonical Ed25519 private scalar), and use 224-bit child scalars. -- Tony Arcieri

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GNU Guix and Tor Browser Packaging
by bancfc＠openmailbox.org 11 Apr '17

11 Apr '17

There is a serious Tor Browser packaging effort [3][4] being done by ng0 (GNUnet dev) for the GNU Guix [0] package manager. GNU Guix supports transactional upgrades and roll-backs, unprivileged package management, per-user profiles and most importantly reproducible builds. I have checked with Guix's upstream and they are working on making a binary mirror available over a Tor Hidden Service. [2] Also planned is resilience [2] to the attack outlined in the TUF threat model. [1] Back to the topic of Tor Browser packaging. While there are good reasons for Debian's pakaging policies they make packaging of fast evolving software (and especially with TBB's reliance on a opaque binary VM for builds) impractial. Both we and Micah have been doing a good effort to automate downloading and validating TBB but I still believe its a maintenance burden and Guix may be a way out of that for Linux distros in general. What are your thoughts on this? *** [0] https://www.gnu.org/software/guix/ [1] https://github.com/theupdateframework/tuf/blob/develop/SECURITY.md [2] https://lists.gnu.org/archive/html/guix-devel/2017-03/msg00192.html [3] https://lists.gnu.org/archive/html/guix-devel/2017-03/msg00189.html [4] https://lists.gnu.org/archive/html/guix-devel/2017-03/msg00149.html

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Comments on proposal 279 (Name API)
by Nick Mathewson 09 Apr '17

09 Apr '17

Hi ! I'll make some comments here on the draft onion naming API at https://gitweb.torproject.org/torspec.git/tree/proposals/279-naming-layer-a… (Some of these are probably things you already meant, or already said elsewhere.) Section 2.1 and elsewhere: I suggest that we require all address suffixes to end with .onion; other TLDs are not reserved like .onion is, and maybe we shouldn't squat any we haven't squatted already. I think we might also want to have all output addresses end with .onion too. I suggest also that we might want to reserve part of the namespace for standardized namespaces and some for experimental or local ones. Like, if we standardize on namecoin that could be .bit.onion, but if we don't, it could be .bit.x.onion. I finally suggest that we distinguish names that are supposed to be global from ones that aren't. Section 2.3: How about we require that the suffixes be distinct? If we do that, we can drop this "priority" business and we can make the system's behavior much easier to understand and explain. Let's require that the TLDs actually begin with a dot. (That is, I think that ".foo.onion" can include "bar.foo.onion", but I don't like the idea of "foo.onion" including "barfoo.onion".) Section 2.3.1: Does the algorithm apply recursively? That is, can more then one plugin rewrite the same address, or can one plugin rewrite its own output? (I would suggest "no".) I think there should be a way for a plugin to say "This address definitely does not exist" and stop resolution. Otherwise no plugin can be authoritative over a TLD. Section 2.5.1: Is the algorithm allowed to produce non-onion addresses? Should it be? Must query IDs be unique? Over what scope must they be unique? Who enforces that? May query IDs be negative? Can they be arbitrarily large? I think result should indeed be optional on failure. Section 2.5.1 and 2.5.2: We should specify what exactly clients and plugins will do if they receive an unrecognized message, or a malformed message. Section 2.5.3. See security notes on caching below; client-side caching can lead to undesirable results. As noted above, I agree with requiring all result addresses to be .onion. Section 3.1: I prefer the "put everything under .onion" option. I also think that we should require that the second-level domain be 10 characters or less, to avoid confusion with existing onion addresses. General questions: I know we've done stdout/stdin for communication before, but I wonder if we should consider how well it's worked for us. The portability on Windows can be kind of hard. Two alternatives are TCP and named pipes. Another alternative might be just using the DNS protocol and asking for some kind of "ONION_CNAME" record. (DNS is ugly, but at least it's nice and standard.) Security notes: I'd like to know what the browser people think about the risks here of (eg) probing to see whether the user has certain extensions installed or names mapped. Maybe .hosts.onion should only be allowed in the address bar, not in HREF attributes et al? We might want to think about cache-related timing attacks here. Perhaps we should have a "no caching" rule. We should probably add a security notes section for how to write plugins that aren't dangerous: a bad plugin potentially breaks user anonymity.

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GSoC: Support all kinds of DNS queries
by Daniel Achleitner 07 Apr '17

07 Apr '17

Hi everyone, I'm a Software Engineering master's student at TU Wien, Austria, with a recent focus on computer security and privacy issues. I am interested in participating in GSoC 2017, particularily in the task to support all kinds of DNS queries via Tor [1]. I've seen the mailing list discussions of 2012 and read the resulting proposition 219 [2]. What do you think, which parts of it (if any) would need to be adapted for DNS in 2017? My current impression is that not much has changed, particularily regarding DNSSEC support and deployment. As of now, the proposal looks fairly complete with few questions remaining, the biggest research task being how to utilize libunbound for query/response parsing and construction. Implementing the RELAY DNS cells then seems fairly straightforward. Unit/integration tests and some fuzzing would be a good idea. The problem of reducing DNSSEC roundtrips (serialization) to be investigated in a later phase, I would say. Is a separate AXFR tool still something that is desired? I have no experience with zone transfers -- can't the existing tooling just be used over a normal TCP conn through Tor? This project idea would make a good match to my thesis in progress, for which I am researching and evaluating privacy-improving DNS tools in the context of Tor (DNSCrypt, DNS-over-TLS) [3], inspired by the awesome paper on DNS correlation [4]. For example, I recently built a SOCKS-to-SOCKS translator which allows to resolve hostnames using a resolver of choice, e.g. using DNSCrypt with TBB. Looking forward to hearing your thoughts, concerns and opinions! Best regards, Daniel IRC handle on OFTC: idealchain [1]: https://www.torproject.org/getinvolved/volunteer.html.en#supportAllDNS [2]: https://gitweb.torproject.org/torspec.git/tree/proposals/219-expanded-dns.t… [3]: My work-in-progress mindmap about DNS Privacy (not related to prop219): https://drive.google.com/open?id=0B3d38csDsjwudDJOUjRleE93bjQ [4]: https://nymity.ch/dns-traffic-correlation/tor-dns.pdf

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Rethinking Bad Exit Defences: Highlighting insecure and sensitive content in Tor Browser
by Donncha O'Cearbhaill 06 Apr '17

06 Apr '17

Hi all, The Tor bad-relay team regularly detects malicious exit relays which are actively manipulating Tor traffic. These attackers appear financial motivated and have primarily been observed modifying Bitcoin and onion address which are displayed on non-HTTPS web pages. Increasingly these attackers are becoming more selective in their targeting. Some attackers are only targeting a handful of pre-configured pages. As a result, we often rely on Tor users to report bad exits and the URLs which are being targeted. In Firefox 51, Mozilla started to highlight HTTP pages containing password form fields as insecure [1]. This UI clearly and directly highlights the risk involved in communicating sensitive data over HTTP. I'd like to investigate ways that we can extend a similar UI to Tor Browser which highlight Bitcoin and onion addressed served over HTTP. I understand that implementing this type of Bitcoin and onion address detection would be less reliable than Firefox's password field detection. However even if unreliable it could increase safety and increase user awareness about the risks of non-secure transports. There is certainly significant design work that needs to be done to implement this feature. For example, .onion origins need be treated as secure, but only if they don't included resources from non-secure origins. We would also need to make the onion/bitcoin address detection reliable against active obfuscation attempts by malicious exits. I'd like to hear any and all feedback, suggestions or criticism of this proposal. Kind Regards, Donncha [1] https://blog.mozilla.org/security/2017/01/20/communicating-the-dangers-of-n…

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GSoC 2017 - Project "Onionoo"
by Nur-Magomed 03 Apr '17

03 Apr '17

Hi! I’m Nur-Magomed Dzhamiev, 4th year student from institute of information technology (speciality: computer security) of North-Caucasus Federal University. I have experience with Java, SQL, Web (HTML, CSS, JavaScript, PHP) and also I designed protocol based on JSON for Android app. I would love to contribute to the project "Onionoo". Please provide me some guide lines and additional materials for study and get a clear understanding about the mentioned project. Thank you! Regards Nur-Magomed

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Tor in a safer language: Network team update from Amsterdam
by Sebastian Hahn 03 Apr '17

03 Apr '17

Hi there tor-dev, as an update to those who didn't have the chance to meet with us in Amsterdam or those who haven't followed the efforts to rely on C less, here's what happened at the "let's not fight about Go versus Rust, but talk about how to migrate Tor to a safer language" session and what happened after. Notes from session: We didn't fight about Rust or Go or modern C++. Instead, we focused on identifying goals for migrating Tor to a memory-safe language, and how to get there. With that frame of reference, Rust emerged as a extremely strong candidate for the incremental improvement style that we considered necessary. We were strongly advised to not use cgo, by people who have used it extensively. As there are clearly a lot of unknowns with this endeavor, and a lot that we will learn/come up against along the way, we feel that Rust is a compelling option to start with, with the caveat that we will first experiment, learn from the experience, and then build on what we learn. You can also check out the session notes on the wiki (submitted, but not posted yet).[1] The real fun part started after the session. We got together to actually make a plan for an experiment and to give Rust a serious chance. We quickly got a few trivial things working like statically linking Rust into Tor, integrating with the build system to call out to cargo for the Rust build, and using Tor's allocator from Rust. We're planning to write up a blog post summarizing our experiences so far while hopefully poking the Rust developers to prioritize the missing features so we can stop using nightly Rust soon (~months, instead of years). We want to have a patch merged into tor soon so you can all play with your dev setup to help identify any challenges. We want to stress that this is an optional experiment for now, we would love feedback but nobody is paid to work on this and nobody is expected to spend more time than they have sitting around. We have committed to reviewing any patch that includes any Rust code to provide feedback, get experience to develop a style, and actually make use of this experiment. This means we're not ready to take on big patches that add lots of tricky stuff quite now, we want to take it slow and learn from this. We would like to do a session at the next dev meeting to give updates on this effort, but in the meantime, if team members would like to start learning Rust and helping us identify/implement small and well-isolated areas to begin migration, or new pieces of functionality that we can build immediately in Rust, that would be really great. So, for a TLDR: What has already been done: - Rust in Tor build - Putting together environment setup instructions and a (very small) initial draft for coding standards - Initial work to identify good candidates for migration (not tightly interdependent) What we think are next steps: - Define conventions for the API boundary between Rust and C - Add a non-trivial Rust API and deploy with a flag to optionally use (to test support with a safe fallback) - Learn from similar projects - Add automated tooling for Rust, such as linting and testing Cheers Alex, Chelsea, Sebastian [1]: Will be visible here https://trac.torproject.org/projects/tor/wiki/org/meetings/2017Amsterdam/No…

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tor-dev March 2017