tor-dev April 2016

tor-dev@lists.torproject.org

60 participants
61 discussions

Request for feedback/victims: cfc-0.0.3
by Yawning Angel 18 Apr '16

18 Apr '16

Thanks for the feedback/bug reports so far. [ PEOPLE THAT HAVE BIG SCARY ADVERSARIES IN THEIR THREAT MODEL STILL SHOULD NOT USE THIS. ] This is the third release of the archive.is based captcha-be-gone extension for Tor Browser. Relative to 0.0.2, this has a minor bugfix that fixes URLs with trendy "@" signs in odd places by replacing the URI/URL parser (Eg: "https://medium.com/@blahblahblah"). I've been busy with other things so this was the only change, but medium.com is popular enough that it deserved a new XPI. Source: https://git.schwanenlied.me/yawning/cfc XPI: https://people.torproject.org/~yawning/volatile/cfc-20160418/ Regards, -- Yawning Angel

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Re: [tor-dev] Latest state of the guard algorithm proposal (prop259) (April 2016)
by Fan Jiang 18 Apr '16

18 Apr '16

Hi, the last mail got rejected by tor-dev, to keep track of this thread, sending again, sorry for disturbing, > On Fri, Apr 15, 2016 at 5:37 AM, George Kadianakis <desnacked(a)riseup.net> > wrote: > >> Fan Jiang <fanjiang(a)thoughtworks.com> writes: >> >> > [ text/plain ] >> > Thanks for the insights. >> > >> > >> >> >> It seems like the latest version of prop259 was posted a few weeks >> ago: >> >> >> >> >> https://lists.torproject.org/pipermail/tor-dev/2016-March/010625.html >> >> >> >> >> > <snip> >> >> > >> >> >> A few things: >> >> >> >> >> >> a) Are there still proposal design decisions that need to be taken >> and >> >> we >> >> >> are >> >> >> unclear on? I admit I'm a bit lost in the latest [tor-dev] >> thread, so >> >> >> maybe >> >> >> I can be of help somehow here? >> >> >> >> >> >> There are still some issues, like for_directory may leads to >> maintain >> >> two >> >> > sets of >> >> > sampled_set independently, which is not yet defined clearly in >> proposal. >> >> > >> >> >> >> Hm, how come this is happening? >> >> >> >> I would think that for_directory would now be just another filter >> (like the >> >> ipv6 one etc.) that can be applied on top of the sampled list. >> >> >> > The problem here is for_directory is a parameter of function call, that >> > means we can't do filter >> > before the call happens. Now the filter action only happens at START >> stage. >> > Maybe do a check before we return the selected guard (if not valid, then >> > continue picking new one) >> > can be a solution. >> > >> >> Hello, >> >> hm, that's an interesting problem... >> >> So we learn whether a circuit is for_directory when >> choose_random_entry_prop259() is called, but at that point the prop259 >> algorithm has already STARTed and its filtering parameters have been >> determined? >> >> So if some part of tor calls choose_random_entry_prop259() quickly twice, >> first >> with for_directory set, and the second time with for_directory unset, the >> guard >> algorithm will proceed in both cases with for_directory being set? >> Because the >> context has been set in the first call to choose_random_entry_prop259()? >> >> This seems like a problem to me, and I'm not sure how to solve it well... >> >> One way could be to use the 'cpath_build_state_t *state' in >> choose_random_entry_prop259() to be able to understand whether each call >> is >> about a different circuit or not. Then you could start a separate >> algorithm >> invocation (so new START) for each new circuit you see. >> >> But then I'm not sure how to do this without each separate algorithm call >> wrecking up the sampled_guards and used_guards lists... In the dev >> meeting in >> Valencia, we discussed with Ola and Reinaldo about using locking and >> blocking >> for this, but I'm not sure how much that would impact the performance... >> >> Do you guys have any plans here? >> >> We can have two pending_guard one for directory, one for any usage(which > will be picked by the NEXT algo, so they can be same node), > and they can be checked with directory flag before return. > Locking may not work because this algo should at least return sth before > it continues to another one, saying Dir and non-Dir are now in main loop, > Or if you have any ideas please let me know. > >> --- >> >> >> >> BTW, I also noticed that you have various global structures in prop259.c, >> like >> entry_guard_selection and used_guards and sampled_guards. I see you've >> been >> working hard on un-globalizing the entry_guards list, but I'm not sure if >> there >> is value to that if all those other structures are global. Do you have >> plans >> for making those structures local to each specific algorithm instance? >> >> I've been working on moving these other structures into a > guard_selection_t, > and hope it can help to make this algo instanceable. > > >> Cheers! >> >

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putting 'Nuke MyFamily' to vote (#6676)
by nusenu 17 Apr '16

17 Apr '16

One year after my last thread on that topic [0] I'd like to move forward on the question whether tor should have a MyFamily functionality or not, because it seems to be a blocker of prop242 (#5565) and it is clear that the current MyFamily design is not practical for many - given the amount of improper or undeclared families [6]. prop 242 is also relevant in the context of Sibyls because if MyFamily becomes trivially easy for everyone to configure one might even start to use it to tell "good" and "bad" apart. If you have an opinion on that topic please reply. I tried to collect opinions on that from past threads and trac. When Nick asked "So, what do we think?" last year only people in favor of keeping it replied. In favor of keeping it: Nick [1] Teor [2] Virgil [3] Griffin [4] Moritz [5] In favor of nuking MyFamily: rransom anyone? Please speak up. Tools that use/display/process/depend on MyFamily: - tor-roster.org - onionoo - atlas - others? Can we close #6676 if no one is in favor of removing MyFamily? https://trac.torproject.org/projects/tor/ticket/6676 [0] https://lists.torproject.org/pipermail/tor-dev/2015-March/008516.html [1] https://lists.torproject.org/pipermail/tor-dev/2015-March/008517.html [2] https://lists.torproject.org/pipermail/tor-dev/2015-March/008531.html [3] https://lists.torproject.org/pipermail/tor-dev/2015-March/008527.html [4] https://lists.torproject.org/pipermail/tor-dev/2015-March/008529.html [5] https://trac.torproject.org/projects/tor/ticket/6676#comment:8 [6] https://raw.githubusercontent.com/nusenu/tor-network-observations/master/to… https://raw.githubusercontent.com/ornetstats/stats/master/o/potentially_dan…

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Add me
by Ruth Watts 17 Apr '16

17 Apr '16

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Re: [tor-dev] Latest state of the guard algorithm proposal (prop259) (April 2016)
by George Kadianakis 15 Apr '16

15 Apr '16

Fan Jiang <fanjiang(a)thoughtworks.com> writes: > [ text/plain ] > Thanks for the insights. > > >> >> It seems like the latest version of prop259 was posted a few weeks ago: >> >> >> https://lists.torproject.org/pipermail/tor-dev/2016-March/010625.html >> >> >> > <snip> >> > >> >> A few things: >> >> >> >> a) Are there still proposal design decisions that need to be taken and >> we >> >> are >> >> unclear on? I admit I'm a bit lost in the latest [tor-dev] thread, so >> >> maybe >> >> I can be of help somehow here? >> >> >> >> There are still some issues, like for_directory may leads to maintain >> two >> > sets of >> > sampled_set independently, which is not yet defined clearly in proposal. >> > >> >> Hm, how come this is happening? >> >> I would think that for_directory would now be just another filter (like the >> ipv6 one etc.) that can be applied on top of the sampled list. >> > The problem here is for_directory is a parameter of function call, that > means we can't do filter > before the call happens. Now the filter action only happens at START stage. > Maybe do a check before we return the selected guard (if not valid, then > continue picking new one) > can be a solution. > Hello, hm, that's an interesting problem... So we learn whether a circuit is for_directory when choose_random_entry_prop259() is called, but at that point the prop259 algorithm has already STARTed and its filtering parameters have been determined? So if some part of tor calls choose_random_entry_prop259() quickly twice, first with for_directory set, and the second time with for_directory unset, the guard algorithm will proceed in both cases with for_directory being set? Because the context has been set in the first call to choose_random_entry_prop259()? This seems like a problem to me, and I'm not sure how to solve it well... One way could be to use the 'cpath_build_state_t *state' in choose_random_entry_prop259() to be able to understand whether each call is about a different circuit or not. Then you could start a separate algorithm invocation (so new START) for each new circuit you see. But then I'm not sure how to do this without each separate algorithm call wrecking up the sampled_guards and used_guards lists... In the dev meeting in Valencia, we discussed with Ola and Reinaldo about using locking and blocking for this, but I'm not sure how much that would impact the performance... Do you guys have any plans here? --- BTW, I also noticed that you have various global structures in prop259.c, like entry_guard_selection and used_guards and sampled_guards. I see you've been working hard on un-globalizing the entry_guards list, but I'm not sure if there is value to that if all those other structures are global. Do you have plans for making those structures local to each specific algorithm instance? Cheers!

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Proposal: Tor with collective signatures
by Nicolas Gailly 14 Apr '16

14 Apr '16

Hi Tor devs, I'm part of the DeDiS team at EPFL and we are working on Cothority, which is a generic framework for Collective Authority. We worked on a proposal to apply Collective Signatures (CoSi) to D.A. consensus document in the Tor ecosystem. While not adding too much complexity to the Tor ecosystem, we believe it can bring more transparency, accountability and security regarding the consensus documents. There is also a section regarding the emergency procedure that D.A.s operators are under when a relay is detected as malicious, and how CoSi could help in this process. I hope you will find it interesting and welcome all the feedbacks / opinions you can have! Thanks in advance, Nicolas <-------- tor_cosi.txt ---------------> Filename: tor_cosi.txt Title: Tor CoSi Author: Nicolas GAILLY Created: 09.03.2016 Status: draft 0. Introduction This document describes how to provide and use a decentralized witness cosigning mechanism in order to gain proactive transparency and public accountability for the Tor consensus documents. Directory Authorities (DA) send their document to this set of witnesses and embed the signature within the document. Tor relays and clients can choose to refuse a consensus document if it has not been accepted and signed by a threshold of witnesses. 1. Overview A weakness of the current DA system is that if any 5 of the 9 DAs’ keys are stolen or coerced they could be used to sign fake directories that the attacker might use secretly in another part of the world to compromise Tor clients in the attacker’s domain. We propose to address this class of attacks by incorporating decentralized witness cosigning (CoSi) into the directory signing process, which ensures that any consensus document must be not only signed by appropriate DAs, but also publicly witnessed, signed and logged by a larger group of servers acting as witnesses, before clients will accept the directory. A Tor relay or client expects to receive an additional "CoSi" signature alongside the consensus document. They verify if the signature is correct and whether a sufficient number of witnesses attested that the consensus document is valid or not. The Tor project would fix such a threshold in the default configuration but any user or relay is free to adjust this value to its own need. In order to verify the signature, they need to have the individuals public keys of all the witnesses beforehand. This "CoSi certificate" can be embedded in the software in the same way certificate pinning does. 2. Motivation Tor's DAs are comprised of 9 servers (and one extra for the bridges): four of them are in the US and 5 of them are in the EU. Attacking these central and vital points of the Tor network is clearly within the reach of state level adversaries if they were to collaborate. Recent stories about surveillance show that such a collaboration is already happening. For example, let's imagine a plausible situation where a state-level attacker secretly coerces and/or steals the private keys of 5 of the 9 DAs, takes them back to the Republic of Tyrannia where they control the ISPs and the country’s Internet connectivity to the rest of the world. The government embeds those keys in their “Great Firewall” type devices, and uses them to secretly MITM attack targeted Tor users within Tyrannia by giving them correctly-signed but completely false views of the Tor directory in which all of the available relays are run by the Tyrannian authorities. Since this attack does not attack the consensus documents that the legitimate DAs are regularly broadcasting to the rest of the world, neither the Tor project nor anyone else outside of Tyrannia will have the opportunity to see or become aware of the fake consensus documents, and not many people even inside Tyrannia might have the opportunity to detect the attack if it is carefully targeted against the small number of suspected activists and journalists the government does not like. The main goal of CoSi applied in Tor should be to ensure consensus document transparency: that is, ensure the property that any consensus document that any Tor client anywhere will accept has been observed and logged by a significant number of parties throughout the world, so that any misuse of a quorum of 5 DA keys anywhere will be quickly detectable (soon, if not necessarily during the signing process itself). 4. Design The first part will talk more about the architecture of a "CoSi" system and the second part will go into more detail about how such a system can be integrated in Tor. 4.1 Simplified Architecture The designated leader arranges all the witnesses in a tree. The public keys of each participants are aggregated to form an aggregate public key. The tree is only there for performance reasons and can be reconfigured at any point in time without affecting security (the latest experiments showed that we could run up to 8000 nodes with a 2 second delay for generating a signature). Once the tree is constructed, its "certificate" represents the aggregate public key and the hash of a Merkle tree containing all the individual public keys. This Merkle tree is needed in case some nodes are failing, so the verification of the signature can still be executed without any change by the client. These issues are covered later in the “Handling Exceptions” part. In a nutshell, a signature round broadcasts the message down the tree, and to each participant. At the end of a signature round, the client have a simple Schnorr signature to verify. Besides contributing to the signing, each witness can and should perform any readily feasible syntactic and semantic correctness checks on the leader’s proposed statements before signing off on them. They can / should probably publish logs of the statements they witness or simply make available a public mirror of everything that its tree roster has been asked to sign. An important point is that each signature is chained with the last one, so each witness also knows the full set of witnesses that accepted the last signature and whether the leader is acting malicious or not. 4.2 CoSi in Tor 4.2.1 Setup The CoSi system can be constructed using independent, diverse and decentralized witnesses. In the context of Tor, one could imagine to include the DA themselves (one could be the leader), and some of the best relays in term of availability and reputation. Due to the decentralized nature of CoSi, this system can also includes external organizations that are favorable and trusted by Tor (e.g. EFF). Another criteria for the tree construction includes the latency between witnesses. One can collect information about the communication latencies between the witnesses and construct a shortest-path spanning tree using this data in order to reduce the global latency of the system. One important property is that the system is under a closed membership policy. The certificate of the CoSi system will have to be embedded in the Tor code in a similar way as for certificate pinning. One obvious way to do it is to setup the set of witnesses as being the DAs and the set of (future) “backup directory servers” as their public keys will already be hard-coded into the Tor client software. That way the deployment cost is drastically reduced as software will already have the keys to verify a CoSi signature. 4.2.2 Operations Once the tree is setup and each one knows about it (have the certificate), then the signature process happens for each consensus document. The CoSi protocol produces a collective signature in response to the initiation of the protocol by a leader. This signature is then included in the consensus document so clients don't have to request it from another party. One issue for discussion is who should initiate CoSi protocol rounds and at what times. For example, each of the 9 DAs (or whatever subset is online) could independently initiate CoSi rounds on each directory consensus event, producing up to nine separate, redundant collective signatures on each directory consensus. Alternatively, the common case might be for one of the 9 DAs to be the CoSi initiator at a given time, with a round-robin leader-change mechanism ensuring that another leader takes over if the prior one becomes unavailable. A related issue for discussion is whether it could be problematic if there are two or more distinct collective signatures for a given directory consensus, and whether it is a problem if distinct subsets of 5 DAs might (perhaps accidentally) produce multiple slightly different, though valid and legitimately-signed, consensus documents at about the same time. In other words, does Tor directory consensus “need” strong consistency with a single serialized timeline, as Byzantine consensus protocols are intended to provide - or is weak consistency with occasional cases of multiple concurrent consensus documents and/or collective signatures acceptable? 4.2.3 Integration First of all, integrating CoSi would *not* immediately affect the fundamental structure or function of the current DAs: there could still be 9 of them, of which any 5 can authorize the release of a new consensus document, as they do now. Secondly, CoSi would not necessarily change anything about how the 9 DAs decide on how to compute these directory consensus documents; e.g., it would not prevent the DAs from working together to block the inclusion of (or assignment of bandwidth-weight to) relays that might be perceived by the DAs as doing bad things. Finally, full backward compatibility with old Tor clients and relay software may be maintained by treating the new CoSi-generated collective signature as just an additional signature that gets attached to and distributed with consensus documents. It may be treated as a special “10th virtual DA” that does not help authorize decisions but just publicly witnesses the output of the regular 9 DAs. Old client and relay software can simply ignore that new collective signature, whereas new software might look for it and over time gradually increase the threshold number of witnesses it expects to see. 4.3 Optional: Break-the-glass Emergency Directory Adjustments In case of emergency, the delay caused by having to coordinate among 5 DAs in order to make anything happen (i.e. excluding a set of malicious nodes) can be problematic. This section proposes a mechanism in which the CoSi witnesses can accept and witness not just “full consensus” documents (signed by 5 DAs), but can also accept “emergency adjustments”, which are highly-constrained deltas (diffs) to an existing full consensus document signed by a smaller threshold of DAs, e.g., 2 or even just 1. For example, the CoSi witness cosigning rules might require that an emergency directory-adjustment must: - be a diff against a “fresh”, recent full consensus document (perhaps *the* most recent one), - can make no modifications to the full consensus other than some pre-defined operations such as decreasing bandwidth weights assigned to relays, - cannot affect the directory-wide total bandwidth weight by more than X% (e.g., 1% or .1%). These suggestions are just a few imaginable rules to get the idea across; the “right” rules would of course need much more discussion. This way, if one or two DAs discovers or even strongly suspects an attack of some kind, they can take emergency countermeasures against the attack and be able to roll them out to clients quickly without having to get a full 5 DAs out of bed - but because the delta-consensus is still witness-cosigned automatically by (perhaps) all the DAs and a number of additional trusted relays, we get the strong accountability provision that the use of such a “break-the-glass” emergency provision will immediately become known to the other DAs as soon as they do get out of bed. Such a break-the-glass emergency adjustment mechanism could be designed, if desired, so that ordinary clients and relays cannot immediately tell the difference between a directory consensus produced via the normal threshold of 5 DAs and one that was produced as a delta via the emergency adjustment mechanism. Only the witness cosigners would necessarily need to know which collectively-signed directories were authorized via the full consensus procedure or via a break-the-glass adjustment. So if it’s important to keep it secret from the general public the precise reason for a particular directory update, that can be accommodated. Only the more-trusted group of witness cosigners (and obviously all the DAs themselves) would necessarily know the precise origin and administrative justification of a given directory update. With even fancier crypto, even the witnesses would not necessarily need to know, but that’s beyond the scope of this proposal and its desirability may be questionable at any rate. 4. Security implications 4.1 Cons Since the structure is a tree, if any node fails, there must be some failover mechanisms to restore connectivity between the children of the failed node and the rest of the tree. Since the DA reach consensus every hour [1], with the help of the gossiping network, the availability problem is not an issue. 4.2 Benefits Technically, it is quite easy to implement witness cosigning if the group of witnesses is small. If we want the group of witnesses to be large, however – and we do, to ensure that compromising transparency would require not just a few but hundreds or even thousands of witnesses to be colluding maliciously – then gathering hundreds or thousands of individual signatures could become painful and inefficient. Worse, every client would need to check all these signatures individually. The key technical contribution of our research is a distributed protocol that makes large, decentralized witness cosigning groups practical. This decentralized approach enables the security of the whole system to scale with the number of witnesses. Not only does this system dramatically increase the cost of successfully deploying an attack on the DA (the attacker would have to corrupt a large majority of the witnesses), it also decreases the incentive to launch such an attack because the threshold of witnesses that are required to sign the document for the signature to be accepted can be locally set on each client. 4.3 Differences between CoSi and Certificate Transparency Prior transparency mechanisms have two weaknesses. First they do not significantly increase the number of secret keys an attacker must control to compromise any client device, and client devices cannot even retroactively detect such compromise unless they can actively communicate with multiple well-known Internet servers. For example, even with Certificate Transparency, an attacker can forge an Extended Validation (EV) certificate for Chrome after compromising or coercing only three parties: one Certificate Authority (CA) and two log servers. Since many CAs and log servers are in US jurisdiction, such an attack is clearly within reach of the US government. If such an attack does occur, Certificate Transparency cannot detect it unless the victim device has a chance to communicate or gossip the fake certificate with other parties on the Internet – after it has already accepted and started using the fake digital certificate. In the case of Tor Transparency, the attack is harder because the attacker would have to compromise the three parties plus a majority of Directory Authorities but facing a state-level adversary the threat is still plausible. One way to increase the difficulty of the attack is to make sure the logs servers are scattered in different places of the world. Second, the attacker can still evade transparency by controlling the client’s Internet access paths. For example, a compromised Internet service provider (ISP) or corporate Internet gateway can defeat retroactive transparency mechanisms by persistently blocking a victim device’s access to transparency servers elsewhere on the Internet. Even if the user’s device is mobile, a state intelligence service such as China’s “Great Firewall” could defeat retroactive transparency mechanisms by persistently blocking connections from a targeted victim’s devices to external transparency servers, in the same way that China already blocks connections to many websites and Tor relays. Using CoSi requires the clients to have the list of public keys of all the witnesses embedded in the software, like certificate pinning. In order to reduce the size of this CoSi certificate, we embed the aggregated public key of all the witnesses and a hash representing the root of a Merkle tree containing the public key of all the witnesses. Using the certificate this way provides an universally-verifiable commitment to all the witnesses’ public keys, without the certificate actually containing them all. 5. Specifications 6. Compatibility 7. Implementation Implementation in Go is open source at: https://github.com/dedis/cothority 8. Performance 9. Acknowledgments This proposals has received some valuable feedback from Bryan Ford, Linus Gasser, Ismail Khoffi, Philipp Jovanovic, and Ludovic Barman. A. References [1] https://collector.torproject.org <-------------- END ----------------------->

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Re: [tor-dev] Latest state of the guard algorithm proposal (prop259) (April 2016)
by George Kadianakis 14 Apr '16

14 Apr '16

Fan Jiang <fanjiang(a)thoughtworks.com> writes: > [ text/plain ] > Hi George, > > Thanks for following up, > We have been updating the prop259 actively in recent two weeks, > >> >> It seems like the latest version of prop259 was posted a few weeks ago: >> https://lists.torproject.org/pipermail/tor-dev/2016-March/010625.html >> >> My understanding is that since then a few things have changed particularly >> with >> regards to the dystopic heuristic, and the various filtering torrc options. >> More discussion happened in the mailing list, but we have not posted a >> newer version of the proposal yet: >> https://lists.torproject.org/pipermail/tor-dev/2016-April/010714.html >> >> > the newer version of prop259 is sort of feasible again. it's here > https://github.com/twstrike/torspec/blob/review/proposals/259-guard-selecti… > Ah great. Will read it and comment on it ASAP. I notice that the prop now contains many many implementation details (like variable names, etc.). Ideally, we should abstract those details and make them look more like a specification. > And, we have our fork of Tor *running* with new proposal: > https://github.com/twstrike/tor_for_patching/tree/prop259 > How is this going? Does it work as intended? Any graphs? I should find some time and run it myself soon. > > >> A few things: >> >> a) Are there still proposal design decisions that need to be taken and we >> are >> unclear on? I admit I'm a bit lost in the latest [tor-dev] thread, so >> maybe >> I can be of help somehow here? >> >> There are still some issues, like for_directory may leads to maintain two > sets of > sampled_set independently, which is not yet defined clearly in proposal. > Hm, how come this is happening? I would think that for_directory would now be just another filter (like the ipv6 one etc.) that can be applied on top of the sampled list. > <snip> > > c) Let me know if there are any open implementation questions that I could >> assist with. > > > About implementation, one problem is when we try to remove the global > *entry_guards*, > The following functions are still using the global list: > > we already get rid of these: > > //- update_node_guard_status (OK - called from *set_from_config and > // *parse_state. This is an optimization to set the using_as_guard flag.) > //- entry_guards_compute_status (OK - when a new consensus arrives) > //- log_entry_guards (OK - wont be used) > //- add_an_entry_guard (OK - wont be used) > //- entry_guard_register_connect_status (OK - wont be used) > //- entry_guards_set_from_config (OK - wont be used) > //- entry_guards_parse_state and entry_guards_update_state (OK - wont be > used) > //- choose_random_entry_impl (OK - wont be used) > > there are still some remaining: > > //- get_entry_guards() > //- num_live_entry_guards() > //- getinfo_helper_entry_guards() > //- entries_retry_helper() > //- any_bridge_supports_microdescriptors() // Don't quite understand this, > what's a microdescriptors? A microdescriptor is a new type of relay descriptor that is more compact. (well, it used to be new, but it's a few years old these days and most bridges support it afaik). They were introduced to reduce the download sizes of clients, because asking for thousands of normal descriptors required too much bandwidth. Microdescriptors include almost all the details of normal descriptors (like onion keys, etc.) but in a much more succinct format. That function checks if the bridge supports microdescriptors. If yes, it will ask it for its microdescriptor. Otherwise, it will just ask for the normal descriptor. (I'm actually not sure how that function gets away without checking the bridge version or something.) > //- any_bridge_descriptors_known() // Calling choose_random_entry to check > a bridge, which doesn't make sense. > Hah. I didn't know of that function either. That function seems to call choose_random_entry() just to check if bridges have been configured correctly and are ready to use. It doesn't actually use the return value of the function :) Basically, if that func returns not NULL, it means that at least one bridge is live and ready to be attempted. > > > Another issue is about finding a better way to handle configuration > changes, especially for EntryNodes, > UseBridges and ReachableAddresses. The treshould numbers like > N_PRIMARY_GUARDS should be different > in such cases. > Hmm, yes I have not thought how the primary guards heuristic would work when bridges are enabled. Why do you think the thresholds should be different? Thanks for the info. Will try to have feedback on the proposal tomorrow or early next week.

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iObfs: obfs4proxy on iOS
by Mike Tigas 14 Apr '16

14 Apr '16

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA512 [Cross-posted to guardian-dev and tor-dev.] Hey, friends. I suppose this serves as a project announcement of sorts, and also as a progress report regarding the current status of this thing. iObfs is an effort to build obfs4proxy for iOS and to also build out some techniques for actually making it usable within other Tor-enabled iOS apps. You may have heard me or n8fr8 discuss the idea at the dev meeting a few weeks ago. I'm not in love with the name I gave it (it's a placeholder that stuck around), but such is life. The repository is currently hosted at [1]. [1]: https://github.com/mtigas/iObfs The initial sprint is being supported by a small Guardian Project grant through mid-April. The high-level goals are to: 1) successfully cross-compile obfs4proxy for the iOS environment 2) "library-ify" it and link it into a proof-of-concept iOS app 3) figure out how to get it to work without "managed mode" 4) build out a process for maybe putting it into Onion Browser, iCepa[2], and other Tor iOS efforts [2]: https://github.com/iCepa I've got a bit of work regarding #1. I think I'm close to getting the binary running, thanks to the existence of the gomobile tools[3]. Using gomobile, you easily get[4] an "obfs4proxy.app" and (given a properly configured Xcode and iPhone) you can put it on a device. But it crashes right now because (I believe) the iOS SDK requires apps to declare some user interface (even if it's blank). So that's close, but my relative lack of experience with Go and the Go buildchain have made #1/#2 a bit slow-going. [3]: https://golang.org/x/mobile/cmd/gomobile [4]: https://github.com/mtigas/iObfs/blob/master/buildobfs4.sh This week, I also took the time to figure out how PT "managed mode" actually works and now have a good idea of how I'd get obfs4proxy to work in an environment where tor can't fork it as a subprocess. There were some conversations I had during the dev meeting where we thought I'd have to use the control port and manually build circuits or something crazy like that -- but it turns out that the solution is a lot simpler.[5] [5]: https://github.com/mtigas/iObfs/blob/master/notes/obfs4-nonmanaged.md This essentially solves #3, so the big barrier now is cross-compiling, "library-ifying", and linking -- rather than the software implementation bits. Anyway, that's where things are. Progress will surely ramp up a bit over the next few weeks. Comments welcome. Best, Mike Tigas @mtigas | https://mike.tig.as/ | 0xA993E7156E0E9923 -----BEGIN PGP SIGNATURE----- iQEcBAEBCgAGBQJW9wKpAAoJEGQdTjqn+ftyos4IANK+jKe+mdU3IcDGGWp48QnT 34a8DCk4u17MhGnoiPuRVjyF4R380v6+O23lzDsXpDA3bhorBirn1fdkJpnvTsb1 IiS75Q3falq+TPZ5pYCnijFLE0sj0VphdHcZuoiHnn6n8HlYZ13ih9sfZTUg/4pa nxNGL83H62vpuR2voeLWPgfJi+QRVIJVa9zSOz8xE3nE70sGNhbWpWlTn12UbMvj f3QmclTPNAuLCXGANyEG1QkTu+k6lHWCCOcJh/wQmwgWHgfhu3fr+PEq6WpjFqMl 4Znhn7SvLlE1lADT8FnAbfz9ND1rT+BVmhITEnQ11eXcb0YHJOLPN8Fmua+G/eM= =3Daj -----END PGP SIGNATURE-----

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Latest state of the guard algorithm proposal (prop259) (April 2016)
by George Kadianakis 13 Apr '16

13 Apr '16

Greetings STRIKE team! It seems like the latest version of prop259 was posted a few weeks ago: https://lists.torproject.org/pipermail/tor-dev/2016-March/010625.html My understanding is that since then a few things have changed particularly with regards to the dystopic heuristic, and the various filtering torrc options. More discussion happened in the mailing list, but we have not posted a newer version of the proposal yet: https://lists.torproject.org/pipermail/tor-dev/2016-April/010714.html A few things: a) Are there still proposal design decisions that need to be taken and we are unclear on? I admit I'm a bit lost in the latest [tor-dev] thread, so maybe I can be of help somehow here? b) Have you guys updated your version of the torspec based on the mailing list discussions? Is it possible to post the latest version in the mailing list? A few people have enquired about the latest version of the proposal, and I'm hesitant to send them the latest [tor-dev] release of the proposal because maybe too many things have changed since then. c) Let me know if there are any open implementation questions that I could assist with. Cheers!

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Configuring Single Onion Services
by Tim Wilson-Brown - teor 12 Apr '16

12 Apr '16

Hi All, I'm working on proposal 260's Rendezvous Single Onion Services in #17178. They are faster, because they have one hop between the service and the introduction and rendezvous points. But this means that their location is easy to discover (non-anonymous). So we want to come up with a design that makes it hard to configure a non-anonymous service by accident. Here's a cut-down version of an email I sent to tor-onions for feedback, for those who are on both lists: Nick's concern was that users could configure Single Onion Services without realising that it provides no server location anonymity. I initially thought we could change the torrc option name to make this clear. ... I now believe that trying to overload the name of a feature with warnings about its downsides was a mistake. … This would mean that Single Onion Service operators would include in their torrc: SingleOnionMode 1 HiddenServiceDir … ... As a separate issue, I think there are two alternative designs that can prevent users from configuring the feature and then exposing their location unintentionally: Tor2WebMode requires users to add a compilation option: --enable-tor2web-mode We could do this with Single Onion Services as well: --enable-single-onion-mode If SingleOnionMode is configured without the compilation option, tor warns the user and refuses to start. When it is configured, tor warns the user they're non-anonymous, then starts. However, using a compilation option makes the feature harder to test. And Tor2Web operators already don't like having to compile separate binaries. It's likely Single Onion operators would feel similarly. Alternately, we could add a torrc option: NonAnonymousMode If SingleOnionMode is configured without NonAnonymousMode, tor warns the user and refuses to start. When it is configured, tor warns the user they're non-anonymous, then starts. I spoke with Nick on IRC and he's happy with either of these options. I'd like to proceed with the NonAnonymousMode torrc option, unless there are compelling reasons against that design. I hope that this will allow us to get SingleOnionMode merged early in tor 0.2.9. Tim Tim Wilson-Brown (teor) teor2345 at gmail dot com PGP 968F094B ricochet:ekmygaiu4rzgsk6n

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tor-dev April 2016