January 2016 - tor-dev - lists.torproject.org

Proposal: Rendezvous Single Onion Services
by Tim Wilson-Brown - teor 12 Feb '16

12 Feb '16

Hi All, Please find below and attached a proposal: Rendezvous Single Onion Services. This is an updated and expanded version of "Direct Onion Services: Fast-but-not-hidden services”. It also borrows heavily from "Single Onion Services" (Proposal #252). The proposal is available in the branch “feature-17178-rsos” at https://github.com/teor2345/torspec.git <https://github.com/teor2345/torspec.git> as torspec/proposals/ideas/xxx-rend-single-onion.txt Work on this proposal is being tracked in trac ticket #17178 at https://trac.torproject.org/projects/tor/ticket/17178 <https://trac.torproject.org/projects/tor/ticket/17178> There is a basic implementation in the branch “feature-17178-rsos” at https://github.com/teor2345/tor.git <https://github.com/teor2345/tor.git> This can be tested with the chutney branch "feature-17178-rsos” at https://github.com/teor2345/chutney.git <https://github.com/teor2345/chutney.git> using the command: src/test/test-network.sh --flavor rsos-min Regards, Tim ----- Filename: xxx-rend-single-onion.txt Title: Rendezvous Single Onion Services Author: Tim Wilson-Brown, John Brooks, Aaron Johnson, Rob Jansen, George Kadianakis, Paul Syverson, Roger Dingledine Created: 2015-10-17 Status: Draft 1. Overview Rendezvous single onion services are an alternative design for single onion services, which trade service-side location privacy for improved performance, reliability, and scalability. Rendezvous single onion services have a .onion address identical to any other onion service. The descriptor contains the same information as the existing double onion (hidden) service descriptors. The introduction point and rendezvous protocols occur as in double onion services, with one modification: one-hop connections are made from the onion server to the introduction and rendezvous points. This proposal is a revision of the unnumbered proposal Direct Onion Services: Fast-but-not-hidden services by Roger Dingledine, and George Kadianakis at https://lists.torproject.org/pipermail/tor-dev/2015-April/008625.html It incorporates much of the discussion around hidden services since April 2015, including content from Single Onion Services (Proposal #252) by John Brooks, Paul Syverson, and Roger Dingledine. 2. Motivation Rendezvous single onion services are best used by sites which: * Don’t require location anonymity * Would appreciate lower latency or self-authenticated addresses * Would like to work with existing tor clients and relays * Can’t accept connections to an open ORPort Rendezvous single onion services have a few benefits over double onion services: * Connection latency is lower, as one-hop circuits are built to the introduction and rendezvous points, rather than three-hop circuits * Stream latency is reduced on a four-hop circuit * Less Tor network capacity is consumed by the service, as there are fewer hops (4 rather than 6) between the client and server via the rendezvous point Rendezvous single onion services have a few benefits over single onion services: * A rendezvous single onion service can load-balance over multiple rendezvous backends (see proposal #255) * A rendezvous single onion service doesn't need an accessible ORPort (it works behind a NAT, and in server enclaves that only allow outward connections) * A rendezvous single onion service is compatible with existing tor clients, hidden service directories, introduction points, and rendezvous points Rendezvous single onion services have a few drawbacks over single onion services: * Connection latency is higher, as one-hop circuits are built to the introduction and rendezvous points. Single onion services perform one extend to the single onion service’s ORPort only It should also be noted that, while single onion services receive many incoming connections from different relays, rendezvous single onion services make many outgoing connections to different relays. This should be taken into account when planning the connection capacity of the infrastructure supporting the onion service. Rendezvous single onion services are not location hidden on the service side, but clients retain all of the benefits and privacy of onion services. (The rationale for the 'single' and 'double' nomenclature is described in section 7.4 of proposal #252.) We believe that it is important for the Tor community to be aware of the alternative single onion service designs, so that we can reach consensus on the features and tradeoffs of each design. However, we recognise that each additional flavour of onion service splits the anonymity set of onion service users. Therefore, it may be best for user anonymity that not all designs are adopted, or that mitigations are implemented along with each additional flavour. (See sections 8 & 9 for a further discussion.) 3. Onion descriptors The rendezvous single onion descriptor format is identical to the double onion descriptor format. 4. Reaching a rendezvous single onion service as a client Clients reach rendezvous single onion services in an identical fashion to double onion services. The rendezvous design means that clients do not know whether they are talking to a double or rendezvous single onion service, unless that service tells them. (This may be a security issue.) However, the use of a four-hop path between client and rendezvous single onion service may be statistically distinguishable. (See section 8 for further discussion of security issues.) (Please note that this proposal follows the hop counting conventions in the tor source code. A circuit with a single connections between the client and the endpoint is one-hop, a circuit with 4 connections (and 3 nodes) between the client and endpoint is four-hop.) 5. Publishing a rendezvous single onion service To act as a rendezvous single onion service, a tor instance (or cooperating group of tor instances) must: * Publish onion descriptors in the same manner as any onion service, using three-hop circuits. This avoids service blocking by IP address, proposal #224 (next-generation hidden services) avoids blocking by onion address. * Perform the rendezvous protocol in the same manner as a double onion service, but make the intro and rendezvous connections one-hop. (This may allow intro and rendezvous points to block the service.) 5.1. Configuration options 5.1.1 RendezvousSingleOnionServiceNonAnonymousServer The tor instance operating a rendezvous single onion service must make one-hop circuits to the introduction and rendezvous points: RendezvousSingleOnionServiceNonAnonymousServer 0|1 If set, make one-hop circuits between the Rendezvous Single Onion Service server, and the introduction and rendezvous points. This option makes every onion service instance hosted by this tor instance a Rendezvous Single Onion Service. (Default: 0) Because of the grave consequences of misconfiguration here, we have added ‘NonAnonymous’ to the name of the torrc option. Furthermore, Tor MUST issue a startup warning message to operators of the onion service if this feature is enabled. [Should the name start with ‘NonAnonymous’ instead?] As RendezvousSingleOnionServiceNonAnonymousServer modifies the behaviour of every onion service on a tor instance, it is impossible to run hidden (double onion) services and rendezvous single onion services on the same tor instance. This is considered a feature, as it prevents hidden services from being discovered via rendezvous single onion services on the same tor instance. 5.1.2 Recommended Additional Options: Correctness Based on the experiences of Tor2Web with one-hop paths, operators should consider using the following options with every rendezvous single onion service, and every single onion service: UseEntryGuards 0 One-hop paths do not use entry guards. This also deactivates the entry guard pathbias code, which is not compatible with one-hop paths. Entry guards are a security measure against Sybil attacks. Unfortunately, they also act as the bottleneck of busy onion services and overload those Tor relays. LearnCircuitBuildTimeout 0 Learning circuit build timeouts is incompatible with one-hop paths. It also creates additional, unnecessary connections. Perhaps these options should be set automatically on (rendezvous) single onion services. Tor2Web sets these options automatically: UseEntryGuards 0 LearnCircuitBuildTimeout 0 5.1.3 Recommended Additional Options: Performance LongLivedPorts The default LongLivedPorts setting creates additional, unnecessary connections. This specifies no long-lived ports (the empty list). PredictedPortsRelevanceTime 0 seconds The default PredictedPortsRelevanceTime setting creates additional, unnecessary connections. RendPostPeriod 0 seconds This option typically hides the startup time of a hidden service by randomly posting over a 2 hour period. Since single onion services value speed over anonymity, they can post descriptors straight away. (Actually, 30 seconds after they bootstrap, for descriptor stability.) However, we do not recommend setting the following option to 1, unless bug #17359 is resolved so tor onion services can bootstrap without predicted circuits. __DisablePredictedCircuits 0 This option disables all predicted circuits. It is equivalent to: LearnCircuitBuildTimeout 0 LongLivedPorts PredictedPortsRelevanceTime 0 seconds And turning off hidden service server preemptive circuits, which is currently unimplemented (#17360) 5.1.3 Recommended Additional Options: Security We recommend that no other services are run on a rendezvous single onion service tor instance. Since tor runs as a client (and not a relay) by default, rendezvous single onion service operators should set: SocksPort 0 Disallow connections from client applications to the tor network via this tor instance. ClientOnly 1 Even if the defaults file configures this instance to be a relay, never relay any traffic or serve any descriptors. 5.2. Publishing descriptors A single onion service must publish descriptors in the same manner as any onion service, as defined by rend-spec. 5.3. Authorization Client authorization for a rendezvous single onion service is possible via the same methods used for double onion services. 6. Related Proposals, Tools, and Features 6.1. Load balancing High capacity services can distribute load and implement failover by: * running multiple instances that publish to the same onion service directories, * publishing descriptors containing multiple introduction points (OnionBalance), * publishing different introduction points to different onion service directories (OnionBalance upcoming(?) feature), * handing off rendezvous to a different tor instance via control port messages (proposal #255), or by a combination of these methods. 6.2. Ephemeral single onion services (ADD_ONION) The ADD_ONION control port command could be extended to support ephemerally configured rendezvous single onion services. Given that RendezvousSingleOnionServiceNonAnonymousServer modifies the behaviour of all onion services on a tor instance, if it is set, any ephemerally configured onion service should become a rendezvous single onion service. 6.3. Proposal 224 ("Next-Generation Hidden Services") This proposal is compatible with proposal 224, with onion services acting just like a next-generation hidden service, but making one-hop paths to the introduction and rendezvous points. 6.4. Proposal 246 ("Merging Hidden Service Directories and Intro Points") This proposal is compatible with proposal 246. The onion service will publish its descriptor to the introduction points in the same manner as any other onion service. Clients will use the merged hidden service directory and introduction point just as they do for other onion services. 6.5. Proposal 252 ("Single Onion Services") This proposal is compatible with proposal 252. The onion service will publish its descriptor to the introduction points in the same manner as any other onion service. Clients can then choose to extend to the single onion service, or continue with the rendezvous protocol. Running a rendezvous single onion service and single onion service allows older clients to connect via rendezvous, and newer clients to connenct via extend. This is useful for the transition period where not all clients support single onion services. 6.5. Proposal 255 ("Hidden Service Load Balancing") This proposal is compatible with proposal 255. The onion service will perform the rendezvous protocol in the same manner as any other onion service. Controllers can then choose to handoff the rendezvous point connection to another tor instance, which should also be configured as a rendezvous single onion service. 7. Considerations 7.1 Modifying RendezvousSingleOnionServiceNonAnonymousServer at runtime Implementations should not reuse introduction points or introduction point circuits if the value of RendezvousSingleOnionServiceNonAnonymousServer is different than it was when the introduction point was selected. This is because these circuits will have an undesirable length. There is specific code in tor that preserves introduction points on a HUP, if RendezvousSingleOnionServiceNonAnonymousServer has changed, all circuits should be closed, and all introduction points must be discarded. 7.2 Delaying connection expiry Tor clients typically expire connections much faster than tor relays [citation needed]. (Rendezvous) single onion service operators may find that keeping connections open saves on connection latency. However, it may also place an additional load on the service. (This could be implemented by increasing the configured connection expiry time.) 7.3. (No) Benefit to also running a Tor relay In tor Trac ticket #8742, running a relay and hidden onion service on the same tor instance was disabled for security reasons. While there may be benefits to running a relay on the same instance as a rendezvous single onion service (existing connections mean lower latency, it helps the tor network overall), a security analysis of this configuration has not yet been performed. In addition, a potential drawback is overloading a busy single onion service. 6.4 Predicted circuits We should look whether we can optimize further the predicted circuits that Tor makes as a onion service for this mode. 8. Security Implications 8.1 Splitting the Anonymity Set Each additional flavour of onion service, and each additional externally visible onion service feature, provides oportunities for fingerprinting. Also, each additional type of onion service shrinks the anonymity set for users of double onion (hidden) services who require server location anonymity. These users benefit from the cover provided by current users of onion services, who use them for client anonymity, self-authentication, NAT-punching, or other benefits. For this reason, features that shrink the double onion service anonymity set should be carefully considered. The benefits and drawbacks of additional features also often depend on a particular threat model. It may be that a significant number of users and sites adopt (rendezvous) single onion services due to their benefits. This could increase the traffic on the tor network, therefore increasing anonymity overall. However, the unique behaviour of each type of onion service may still be distinguishable from both the client and server ends of the connection. 8.2 Hidden Service Designs can potentially be more secure As a side-effect, by optimizing for performance in this feature, it allows us to lean more heavily towards security decisions for regular onion services. 8.3 One-hop onion service paths may encourage more attacks There's a possible second-order effect here since both encrypted services and hidden services will have foo.onion addresses and it's not clear based on the address whether the service will be hidden -- if *some* .onion addresses are easy to track down, are we encouraging adversaries to attack all rendezvous points just in case? 9. Further Work Further proposals or research could attempt to mitigate the anonymity-set splitting described in section 8. Here are some initial ideas. 9.1 Making Client Exit connections look like Client Onion Service Connections A mitigation to this fingerprinting is to make each (or some) exit connections look like onion service connections. This provides cover for particular types of onion service connections. Unfortunately, it is not possible to make onion service connections look like exit connections, as there are no suitable dummy servers to exit to on the Internet. 9.1.1 Making Client Exit connections perform Descriptor Downloads (Some) exit connections could perform a dummy descriptor download. (However, descriptors for recently accessed onion services are cached, so dummy downloads should only be performed occasionally.) Exit connections already involve a four-hop "circuit" to the server (including the connection between the exit and the server on the Internet). The server on the Internet is not included in the consensus. Therefore, this mitigation would effectively cover single onion services which are not relays. 9.1.2 Making Client Exit connections perform the Rendezvous Protocol (Some) exit connections could perform a dummy rendezvous protocol. Exit connections already involve a four-hop "circuit" to the server (including the connection between the exit and the server on the Internet). Therefore, this mitigation would effectively cover rendezvous single onion services, as long as a dummy descriptor download was also performed occasionally. 9.1.3 Making Single Onion Service rendezvous points perform name resolution Currently, Exits perform DNS name resolution, and changing this behaviour would cause unacceptable connection latency. Therefore, we could make onion service connections look like exit connections by making the rendezvous point do name resolution (that is, descriptor fetching), and, if needed, the introduction part of the protocol. This could potentially *reduce* the latency of single onion service connections, depending on the length of the paths used by the rendezvous point. However, this change makes rendezvous points almost as powerful as Exits, a careful security analysis will need to be performed before this is implemented. There is also a design issue with rendezvous name resolution: a client wants to leave resolution (descriptor download) to the RP, but it doesn't know whether it can use the exit-like protocol with an RP until it has downloaded the descriptor. This might mean that single onion services of both flavours need a different address style or address namespace. We could use .single.onion or something. (This would require an update to the HSDir code.) 9.2 Performing automated and common queries over onion services Tor could create cover traffic for a flavour of onion service by performing automated or common queries via an onion service of that type. In addition, onion service-based checks have security benefits over DNS-based checks. See Genuine Onion, Syverson and Boyce, 2015, at http://www.nrl.navy.mil/itd/chacs/syverson-genuine-onion-simple-fast-flexib… Here are some examples of automated queries that could be performed over an onion service: 9.2.1 torcheck over onion service torcheck ("Congratulations! This browser is configured to use Tor.") could be retrieved from an onion service. Incidentally, this would resolve the exitmap issues in #17297, but it would also fail to check that exit connections work, which is important for many Tor Browser users. 9.2.2 Tor Browser version checks over onion service Running tor browser version checks over an onion service seems to be an excellent use-case for onion services. It would also have the Tor Project "eating its own dogfood", that is, using onion services for its essential services. 9.2.3 Tor Browser downloads over onion service Running tor browser downloads over an onion service might require some work on the onion service codebase to support high loads, load-balancing, and failover. It is a good use case for a (rendezvous) single onion service, as the traffic over the tor network is only slightly higher than for Tor Browser downloads over tor. (4 hops for [R]SOS, 3 hops for Exit.) 9.2.4 SSL Observatory submissions over onion service HTTPS certificates could be submitted to HTTPS Everywhere's SSL Observatory over an onion service. This option is disabled in Tor Browser by default. Perhaps some users would be more comfortable enabling submission over an onion service, due to the additional security benefits. -----

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Proposal: Load-balancing hidden services by splitting introduction from rendezvous
by Tom van der Woerdt 12 Feb '16

12 Feb '16

Hey all, I'd like your thoughts and comments on this proposal. Tom PS: If you want to deliver them in person, I'm in Berlin. Filename: xxx-intro-rendezvous-controlsocket.txt Title: Load-balancing hidden services by splitting introduction from rendezvous Author: Tom van der Woerdt Created: 2015-09-30 Status: draft 1. Overview and motivation To address scaling concerns with the onion web, we want to be able to spread the load of hidden services across multiple machines. OnionBalance is a great stab at this, and it can currently give us 60x the capacity by publishing 6 separate descriptors, each with 10 introduction points, but more is better. This proposal aims to address hidden service scaling up to a point where we can handle millions of concurrent connections. The basic idea involves splitting the 'introduce' from the 'rendezvous', in the tor implementation, and adding new events and commands to the control specification to allow intercepting introductions and transmitting them to different nodes, which will then take care of the actual rendezvous. External controller code could relay the data to another node or a pool of nodes, all which are run by the hidden service operator, effectively distributing the load of hidden services over multiple processes. By cleverly utilizing the current descriptor methods, we could publish up to sixty unique introduction points, which could translate to many thousands of parallel tor workers. This should allow hidden services to go multi-threaded, with a few small changes. 2. Specification We propose two additions to the control specification, of which one is an event and the other is a new command. We also introduce a new configuration option. 2.1. DisableAutomaticRendezvous configuration option The syntax is: "DisableAutomaticRendezvous" SP [1|0] CRLF This configuration option is defined to be a boolean toggle which, if set, stops the tor implementation from automatically doing a rendezvous when an INTRODUCE2 cell is received. Instead, an event will be sent to the controllers. If no controllers are present, the introduction cell should be dropped, as acting on it instead of dropping it could open a window for a DoS. For security reasons, the configuration should be made available only in the configuration files, and not as an option settable by the controller. 2.2. The "INTRODUCE" event The syntax is: "650" SP "INTRODUCE" SP RendezvousData CRLF RendezvousData = implementation-specific, but must not contain whitespace, must only contain human-readable characters, and should be no longer than 512 bytes The INTRODUCE event should contain sufficient data to allow continuing the rendezvous from another Tor instance. The exact format is left unspecified and left up to the implementation. From this follows that only matching versions can be used safely to coordinate the rendezvous of hidden service connections. 2.3. "PERFORM-RENDEZVOUS" command The syntax is: "PERFORM-RENDEZVOUS" SP RendezvousData CRLF This command allows a controller to perform a rendezvous using data received through an INTRODUCE event. The format of RendezvousData is not specified other than that it must not contain whitespace, and should be no longer than 512 bytes. 3. Compatibility and security The implementation of these methods should, ideally, not change anything in the network, and all control changes are opt-in, so this proposal is fully backwards compatible. Controllers handling this data must be careful to not leak rendezvous data to untrusted parties, as it could be used to intercept and manipulate hidden services traffic. 4. Example Let's take an example where a client (Alice) tries to contact Bob's hidden service. To do this, Bob follows the normal hidden service specification, except he sets up ten servers to do this. One of these publishes the descriptor, the others have this desabled. When the INTRODUCE2 cell arrives at the node which published the descriptor, it does not immediately try to perform the rendezvous, but instead outputs this to the controller. Through an out-of-band process this message is relayed to a controller of another node of Bob's, and this transmits the "PERFORM-RENDEZVOUS" command to that node. This node finally performs the rendezvous, and will continue to serve data to Alice, whose client will now not have to talk to the introduction point anymore. 5. Other considerations We have left the actual format of the rendezvous data in the control protocol unspecified, so that controllers do not need to worry about the various types of hidden service connections, most notably proposal 224. The decision to not implement the actual cell relaying in the tor implementation itself was taken to allow more advanced configurations, and to leave the actual load-balancing algorithm to the implementor of the controller. The developer of the tor implementation should not have to choose between a round-robin algorithm and something that could pull CPU load averages from a centralized monitoring system.

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Proposal: Load Balancing with Overhead Parameters
by Mike Perry 31 Jan '16

31 Jan '16

This proposal aims to allow us to load balance properly between Guard, Middle, and Exit nodes with the addition of padding traffic to the network. Canonical proposal current lives in my load_balancing-squashed branch: https://gitweb.torproject.org/user/mikeperry/torspec.git/tree/proposals/xxx… Here is the text in-line, for ease of commenting on-list: ============================================================== Filename: xxx-load-balancing-with-overhead.txt Title: Load Balancing with Overhead Parameters Authors: Mike Perry Created: 01 January 2016 Status: Draft 0. Motivation In order to properly load balance in the presence of padding and non-negligible amounts of directory and hidden service traffic, the load balancing equations in Section 3.8.3 of dir-spec.txt are in need of some modifications. In addition to supporting the idea of overhead, the load balancing equations can also be simplified by treating Guard+Exit nodes as Exit nodes in all cases. This causes the 9 sub-cases of the current load balancing equations to consolidate into a single solution, which also will greatly simplify the consensus process, and eliminate edge cases such as #16255[1]. 1. Overview For padding overhead due to Proposals 251 and 254, and changes to hidden service path selection in Proposal 247, it will be useful to be able to specify a pair of parameters that represents the additional traffic present on Guard and Middle nodes due to these changes. The current load balancing equations unfortunately make this excessively complicated. With overhead factors included, each of the 9 subcases goes from being a short solution to over a page of calculations for each subcase. Moreover, out of 8751 hourly consensus documents produced in 2015[2], only 78 of them had a non-zero weight for using Guard+Exit nodes in the Guard position (weight Wgd), and most of those were well under 1%. The highest weight for using Guard+Exits in the Guard position recorded in 2015 was 2.62% (on December 10th, 2015). This means clients that chose a Guard node during that particular hour used only 2.62% of Guard+Exit flagged nodes' bandwidth when performing a bandwidth-weighted Guard selection. All clients that chose a Guard node during any other hour did not consider Guard+Exit nodes at all as potential candidates for their Guards. This indicates that we can greatly simplify these load balancing equations with little to no change in diversity to the network. 2. Simplified Load Balancing Equations Recall that the point of the load balancing equations in section 3.8.3 of dir-spec.txt is to ensure that an equal amount of client traffic is distributed between Guards, Middles, Exits, and Guard+Exits, where each flag type can occupy one or more positions in a path. This allocation is accomplished by solving a system of equations for weights for flag position selection to ensure equal allocation of client traffic for each position in a circuit. If we ignore overhead for the moment and treat Guard+Exit nodes as Exit nodes, then this allows the simplified system of equations to become: Wgg*G == M + Wme*E + Wmg*G # Guard position == middle position Wgg*G == Wee*E # Guard position == equals exit position Wmg*G + Wgg*G == G # Guard allocation weights sum to 1 Wme*E + Wee*E == E # Exit allocation weights sum to 1 This system has four equations and four unknowns, and by transitivity we ensure that allocated capacity for guard, middle, and exit positions are all equal. Unlike the equations in 3.8.3 of dir-spec.txt, there are no special cases to the solutions of these equations because there is no shortage of constraints and no decision points for allocation based on scarcity. Thus, there is only one solution. Using SymPy's symbolic equation solver (see attached script) we obtain: E + G + M E + G + M 2*E - G - M 2*G - E - M Wee: ---------, Wgg: ---------, Wme: -----------, Wmg: ------------ 3*E 3*G 3*E 3*G For the rest of the flags weights, we will do the following: Dual-flagged (Guard+Exit) nodes should be treated as Exits: Wgd = 0, Wmd = Wme, Wed = Wee Directory requests use middle weights: Wbd=Wmd, Wbg=Wmg, Wbe=Wme, Wbm=Wmm Handle bridges and strange exit policies: Wgm=Wgg, Wem=Wee, Weg=Wed 2.1. Checking for underflow and overflow In the old load balancing equations, we required a case-by-case proof to guard against overflow and underflow, and to decide what to do in the event of various overflow and underflow conditions[3]. Even still, the system proved fragile to changes, such as the implementation of Guard uptime fractions[1]. Here, with the simplified equations, we can plainly see that the only time that a negative weight can arise is in Wme and Wmg, when 2*E < G+M or when 2*G < E+M. In other words, only when Exits or Guards are scarce. Similarly, the only time that a weight exceeding 1.0 can arise is in Wee and Wgg, which also happens when 2*E < G+M or 2*G < E+M. This means that parameters will always overflow in pairs (Wee and Wme, and/or Wgg and Wmg). In both these cases, simply clipping the parameters at 1 and 0 provides as close of a balancing condition as is possible, given the scarcity. 3. Load balancing with Overhead Parameters Intuitively, overhead due to padding and path selection changes can be represented as missing capacity in the relevant position. This means that in the presence of a Guard overhead fraction of G_o and a Middle overhead fraction of M_o, the total fraction of actual client traffic carried in those positions is (1-G_o) and (1-M_o), respectively. Then, to achieve a balanced allocation of traffic, we consider only the actual client capacity carried in each position: # Guard position minus overhead matches middle position minus overhead: (1-G_o)*(Wgg*G) == (1-M_o)*(M + Wme*E + Wmg*G) # Guard position minus overhead matches exit position: (1-G_o)*(Wgg*G) == 1*(Wee*E) # Guard weights still sum to 1: Wmg*G + Wgg*G == G # Exit weights still sum to 1: Wme*E + Wee*E == E Solving this system with SymPy unfortunately yields some unintuitively simplified results. For each weight, we first show the SymPy solution, and then factor that solution into a form analogous to Section 2: -(G_o - 1)*(M_o - 1)*(E + G + M) Wee: --------------------------------------- E*(G_o + M_o - (G_o - 1)*(M_o - 1) - 2) (1 - G_o)*(1 - M_o)*(E + G + M) Wee: --------------------------------------- E*(2 - G_o - M_o + (1 - G_o)*(1 - M_o)) (M_o - 1)*(E + G + M) Wgg: --------------------------------------- G*(G_o + M_o - (G_o - 1)*(M_o - 1) - 2) (1 - M_o)*(E + G + M) Wgg: --------------------------------------- G*(2 - G_o - M_o + (1 - G_o)*(1- M_o)) -E*(M_o - 1) + G*(G_o - 1)*(-M_o + 2) - M*(M_o - 1) Wmg: --------------------------------------------------- G*(G_o + M_o - (G_o - 1)*(M_o - 1) - 2) (2 - M_o)*G*(1 - G_o) - M*(1 - M_o) - E*(1 - M_o) Wmg: --------------------------------------------------- G*(2 - G_o - M_o + (1 - G_o )*(1 - M_o)) E*(G_o + M_o - 2) + G*(G_o - 1)*(M_o - 1) + M*(G_o - 1)*(M_o - 1) Wme: ----------------------------------------------------------------- E*(G_o + M_o - (G_o - 1)*(M_o - 1) - 2) (2 - G_o - M_o)*E - G*(1 - G_o)*(1 - M_o) - M*(1 - G_o)*(1 - M_o) Wme: ----------------------------------------------------------------- E*(2 - G_o - M_o + (1 - G_o)*(1 - M_o)) A simple spot check with G_o = M_o = 0 shows us that with zero overhead, these solutions become identical to the solutions in Section 2 of this proposal. The final condition that we need to ensure is that these weight values never become negative or greater than 1.0[3]. 3.1. Ensuring against underflow and overflow Note that if M_o = G_o = 0, then the solutions and the overflow conditions are the same as in Section 2. Unfortunately, SimPy is unable to solve multivariate inequalities, which prevents us from directly deriving overflow conditions for each variable independently (at least easily and without mistakes). Wolfram Alpha is able to derive closed form solutions to some degree for this, but they are more complicated than checking the weights for underflow and overflow directly. However, for all overflow and underflow cases, simply warning in the event of overflow or underflow in the weight variable solutions above is equivalent anyway. Optimal load balancing given this scarcity should still result if we clip the resulting solutions to [0, 1.0]. It will be wise in the implementation to test the overflow conditions with M_o = G_o = 0, and with their actual values. This will allow us to know if the overflow is a result of inherent unbalancing, or due to input overhead values that are too large (and need to be reduced by, for example, reducing padding). 4. Consensus integration 4.1. Making use of the Overhead Factors In order to keep the consensus process simple on the Directory Authorities, the overhead parameters represent the combined overhead from many factors. The G_o variable is meant to account for sum of directory overhead, netflow padding overhead, future two-hop padding overhead, and future hidden service overhead (for cases where Guard->Middle->Exit circuits are not used). The M_o variable is meant to account for multi-hop padding overhead, hidden service overhead, as well as an overhead for any future two-hop directory connections (so that we can consolidate Guards and Directory guard functionality into a single Guard node). There is no need for an E_o variable, because even if there were Exit-specific overhead, it could be represented by an equivalent reductions in both G_o and M_o instead. Since all relevant padding and directory overhead information is included in the extra-info documents for each relay, the M_o and G_o variables could be computed automatically from these extra-info documents during the consensus process. However, it is probably wiser to keep humans in the loop and set them manually as consensus parameters instead, especially since we have not previously had to deal with serious adversarial consequences from malicious extra-info reporting. For clarity, though, it may be a good idea to separate all of the components of M_o and G_o into separate consensus parameters, and combine them (via addition) in the final equations. That way it will be easier to pinpoint the source of any potential overflow issues. This separation will also enable us to potentially govern padding's contribution to the overhead via a single tunable value. 4.2 Integration with Guardfraction The GuardFraction changes in Proposal 236 and #16255 should continue to work with these new equations, so long as the total T, G, and M values are counted after the GuardFraction multiplier has been applied. 4.3. Guard flag assignment Ideally, the Guard flag assignment process would also not count Exit-flagged nodes when determining the Guard flag uptime and bandwidth cutoffs, since we will not be using Guard+Exit flagged nodes as Guard nodes at all when this change is applied. This will result in more accurate thresholds for Guard node status, as well as better control over the true total amount of Guard bandwidth in the consensus. 1. https://trac.torproject.org/projects/tor/ticket/16255 2. https://collector.torproject.org/archive/relay-descriptors/consensuses/ 3. http://tor-dev.torproject.narkive.com/17H9FewJ/correctness-proof-for-new-ba… Appendix A: SymPy Script for Balancing Equation Solutions #!/usr/bin/python from sympy.solvers import solve from sympy import simplify, Symbol, init_printing, pprint # Sympy variable declarations (G,M,E,D) = (Symbol('G'),Symbol('M'),Symbol('E'),Symbol('D')) (Wgd,Wmd,Wed,Wme,Wmg,Wgg,Wee) = (Symbol('Wgd'),Symbol('Wmd'),Symbol('Wed'), Symbol('Wme'),Symbol('Wmg'),Symbol('Wgg'), Symbol('Wee')) (G_o, M_o) = (Symbol('G_o'),Symbol('M_o')) print "Current Load Balancing Equation Solutions, Case 1:" pprint(solve( [Wgg*G + Wgd*D - (M + Wmd*D + Wme*E + Wmg*G), Wgg*G + Wgd*D - (Wee*E + Wed*D), Wed*D + Wmd*D + Wgd*D - D, Wmg*G + Wgg*G - G, Wme*E + Wee*E - E, Wmg - Wmd, 3*Wed - 1], Wgd, Wmd, Wed, Wme, Wmg, Wgg, Wee)) print print "Case 1 with guard and middle overhead: " pprint(solve( [(1-G_o)*(Wgg*G + Wgd*D) - (1-M_o)*(M + Wmd*D + Wme*E + Wmg*G), (1-G_o)*(Wgg*G + Wgd*D) - (Wee*E + Wed*D), Wed*D + Wmd*D + Wgd*D - D, Wmg*G + Wgg*G - G, Wme*E + Wee*E - E, Wmg - Wmd, 3*Wed - 1], Wgd, Wmd, Wed, Wme, Wmg, Wgg, Wee)) print "\n\n" print "Elimination of combined Guard+Exit flags (no overhead): " pprint(solve( [(Wgg*G) - (M + Wme*E + Wmg*G), (Wgg*G) - 1*(Wee*E), Wmg*G + Wgg*G - G, Wme*E + Wee*E - E], Wme, Wmg, Wgg, Wee)) print print "Elimination of combined Guard+Exit flags (Guard+middle overhead): " combined = solve( [(1-G_o)*(Wgg*G) - (1-M_o)*(M + Wme*E + Wmg*G), (1-G_o)*(Wgg*G) - 1*(Wee*E), Wmg*G + Wgg*G - G, Wme*E + Wee*E - E], Wme, Wmg, Wgg, Wee) pprint(combined)

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Fwd: Need to know if this is a bug
by Siddhartha De 29 Jan '16

29 Jan '16

Dear all , I just found out that the tor.exe included in the Tor Browser ( ver 5.5 ) for Windows bundle ( Tor ver 0.2.7.6 ) does not support TransPort and TransListenAddress ... The error message given was :- Jan 29 23:16:24.129 [warn] Failed to parse/validate config: TransPort and TransListenAddress are disabled in this build. Jan 29 23:16:24.129 [err] Reading config failed--see warnings above. Is this a deliberate design consideration or a bug ... If we keep the tor.exe of both the browser bundle and expert bundles synced I think it would be easier for users who would like to use Tor both as a browser as well as a Transparent Proxy . Thanking you , Yours sincerely , Siddhartha De

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Re: [tor-dev] Fwd: [guardian-dev] RC-7 is out - try to repro? Re: towards reproducible Orbot
by Nathan Freitas 29 Jan '16

29 Jan '16

On Thu, Jan 28, 2016, at 02:27 PM, Ximin Luo wrote: > Hey, thanks for this! > > I'd like to ask please upload this (or 15.1) to F-Droid soon. The version > currently in F-Droid is RC-4 and is broken with orwall - > orwall-allowed/redirected apps see no internet, but tor is connected and > orfox can access it. RC-7 fixes this issue, I just tested it out. Yes, will do. Thanks for testing.

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Proposals should have reviews. Let's make sure that happens. Here's a schedule.
by Nick Mathewson 29 Jan '16

29 Jan '16

So, one of the longstanding problems with Tor's (change) proposal system has been that proposals sit around for a long time without sufficient discussion or approval. When they're about to be implemented, we do an informal "hey did anybody look at that?" check, but that's not really good enough. Here's what I've been thinking of doing, as discussed at the tor dev IRC meeting yesterday. 1. Everybody who will review proposals* should nominate one or two proposals currently in state "Open" or "Draft". People should nominate proposals that they themselves didn't write. 2. I'll schedule review & discussion sessions, about one per week, trying to hit times where interested people can make it. Everybody who will review proposals* should try to show up if they can, having read the proposal or proposals under discussion for that week. Then we talk about the proposal(s)! 3. We'll try to move nominated proposals towards "Accepted" or "Rejected", improving them as necessary. * I'm not going to be too elitist here, but: If you show up and contribute usefully to discussions, I will prioritize your nominations more than I will prioritize nominations from people who don't contribute so much. This is a draft process, so we'll try to see after a month or two (possibly at the next face-to-face dev meeting?) how it's going. Here's the schedule I have in mind for the first meeting, based on proposals already nominated at the IRC dev meeting. I'm going to go a bit aggressively for the first couple of weeks, so that we can get a sense of how this process works out. Everything is subject to change. We'll be putting notes online from these meetings. Tuesday January 19: 11am Eastern (1600 UTC) Guard node proposals! We'll be talking about these proposals: Prop#259: New Guard Selection Behaviour [DRAFT] Prop#241: Resisting guard-turnover attacks [DRAFT] Prop#247: Defending Against Guard Discovery Attacks using Vanguards [DRAFT] Friday January 22: 11 am Eastern (1600 UTC) Prop#251: Padding for netflow record resolution reduction [DRAFT] Monday January 25: 8pm Eastern (0100 UTC on Tuesday Jan 26) Prop#250: Random Number Generation During Tor Voting [DRAFT] Friday January 29: 8:30 am eastern (1330 UTC) Prop#252: Single Onion Services [DRAFT] Prop#260: Rendezvous Single Onion Services [DRAFT] Prop#246: Merging Hidden Service Directories and Introduction Points [OPEN] Also nominated are: Prop#264: Putting version numbers on the Tor subprotocols [OPEN] Prop#257: Refactoring authorities and taking parts offline [DRAFT] Prop#258: Denial-of-service resistance for directory authorities [OPEN] -- Nick

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Fwd: [guardian-dev] RC-7 is out - try to repro? Re: towards reproducible Orbot
by Nathan Freitas 28 Jan '16

28 Jan '16

With this release and updates to our build process, we are close to having Orbot be reproducible. Otherwise, this should be the last RC for v15.1, and it now includes built-in Obfs4, Obfs3, Scramblesuit bridges from TBB, plus a few new ones from Nima. This will make it much easier for users in places who need bridges to be able to use them without taking an extra step. ----- Original message ----- From: Nathan of Guardian <nathan(a)guardianproject.info> To: guardian-dev(a)lists.mayfirst.org Subject: [guardian-dev] RC-7 is out - try to repro? Re: towards reproducible Orbot Date: Thu, 28 Jan 2016 10:12:59 -0500 On Wed, Jan 27, 2016, at 10:10 AM, Hans-Christoph Steiner wrote: > >>>>> Then anyone will be able to run this to verify the build: > >>>>> > >>>>> git checkout 15.1.0-RC-4 > >>>>> ./make-release-build > >>>>> ./compare-to-official-release ~/Downloads/Orbot-v15.1.0-RC-4.apk \ > >>>>> bin/Orbot-v15.1.0-RC-4.apk I've just posted RC7 built from make-release-build. I haven't attempted to run the compare script yet, so if someone out there wants to try, that would be great. My bet is that I didn't do something right, and it won't match, but I would love to be proven wrong! APK: https://guardianproject.info/releases/Orbot-v15.1.0-RC-7.apk Sig: https://guardianproject.info/releases/Orbot-v15.1.0-RC-7.apk.asc /** 15.1.0-RC-7 / 27-January-2016 / 91225ab053d0ffec4a414be461ee41e6465446bd **/ * fd45fa3 enable TransProxy and DNSPort by default without root - some users run their own iptables transproxy scripts with AFWall and n /** 15.1.0-RC-6 / 27-January-2016 / a8dbdacbcb2412bb08c4a665145371c3ac4abef1 **/ Fixes to enable/attempt reproducible builds for this release * 226d92e make-release-build: env vars need to be first on the command line * 20c16ae ignore more files generated by the build * 9883a89 faketime is only needed when building, not when cleaning * eaa2dde explicitly indicate we are building armeabi * 1b76c36 add make calls for both armeabi and x86 with clean * 75eb36e remove lib binaries * 3be93a0 only build for x86 and armeabi ...and one small UI bug: 1839b8f add-in missing "break" for Meek Google -- Nathan of Guardian nathan(a)guardianproject.info _______________________________________________ List info: https://lists.mayfirst.org/mailman/listinfo/guardian-dev To unsubscribe, email: guardian-dev-unsubscribe(a)lists.mayfirst.org

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Getting people started on guard selection algorithms [prop259]
by George Kadianakis 28 Jan '16

28 Jan '16

Hello Nick, isis and Mike! It seems like some Thoughtworks folks (from here on referred to as FRITO [0]) are interested in helping us with Tor hidden services development for 4 weeks or so. They start early next week! :) They were looking for a coding project that is tractable within a month given a team of four people. Also, it should be fun, interesting and be related to hidden services. One of the projects we discussed and found potentially fitting was proposal 259: https://gitweb.torproject.org/torspec.git/tree/proposals/259-guard-selectio… It is my undertanding that the next steps here involve implementing the various proposed algorithms and evaluating how they cope in some simulated scenarios. Nick and Isis started working on this in Python here: https://github.com/isislovecruft/guardsim You can find the scenarios that need to be tested here: https://github.com/isislovecruft/guardsim/blob/master/doc/stuff-to-test.txt This project seems quite suitable for the FRITO crew :) The idea here is that after we decide which one is the best algorithm to use, we would implement it for little-t-tor in C. The best algorithm is the one that achieves the greatest reachability and security tradeoff. The algorithm should also be designed in such a way that fits into the tor asynchronous networking API. It would be amazing if FRITO could help us here as well, but maybe we can start up with the Python simulation and see if they like the project! Isis and Nick, are you currently working on the guardsim code? Would you be OK if it was taken over by FRITO? Any advice for them? Also, is there a ticket we should be using for this project? If not, I will make one ASAP. Cheers! [0]: FRITO is derived from their names: Fan, Reinaldo, Ivan, Tania and Ola. They are all CCed. PS: We recently did a reading group about prop259 and a few other proposals that you might find interesting. The minutes can be found here: https://lists.torproject.org/pipermail/tor-dev/2016-January/010265.html and the raw logs here: http://meetbot.debian.net/tor-dev/2016/tor-dev.2016-01-19-16.03.log.html

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Tor not affected by recent openssl security advisories
by Nick Mathewson 28 Jan '16

28 Jan '16

Somebody always asks whether Tor is affected by each OpenSSL advisory, so I'm sending this mail in order to get a URL to send people to. :) Here are today's advisories: https://mta.openssl.org/pipermail/openssl-announce/2016-January/000061.html With respect to the first ( "DH small subgroups (CVE-2016-0701)" ), Tor is not affected because we set the SSL_OP_SINGLE_DH_USE() option. We started setting this option back in Tor 0.1.1.9-alpha, back in 2005. With respect to the second ( "SSLv2 doesn't block disabled ciphers (CVE-2015-3197)" ), Tor is not affected because we disable SSLv2 by setting SSL_OP_NO_SSLv2. We started setting this option in Tor 0.0.2pre8, back in 2003. Of course, other applications that you use over Tor may be affected, even though Tor is not; please remember to upgrade them as patches become available. best wishes, -- Nick

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Proposal 247: Alternate Path Lengths
by Mike Perry 27 Jan '16

27 Jan '16

While discussing proposal 247 with George yesterday, we realized that we still get security benefit from additional ephemeral hops beyond the vanguards themselves. Recall the high-level 247 path design is: C - L - M - S -- S - M - L - H Where: C = Client L = Long lived Layer1 guard M = Medium lifespan Layer2 guard S = Short lifespan Layer3 guard H = Hidden Service (or hsdir) E = Ephemeral Hop (used below) I = Intro Point (used below) R = Rend Point (used below) The benefit to just one more hop is easiest to see in the Introduction Point case, where George and I reasoned that it probably is a good idea to pick an intro point that is not the same as the Layer3 (S) set, otherwise the hidden service is effectively publishing its Layer3 guards in its descriptor, and using those same nodes to connect to rendezvous points. Clients probably also do not want the multi-visit linkability of using their layer3 vanguards to directly connect to an HS intro point. This means the intro circuit becomes: C - L - M - S - E -- I - S - M - L - H Similarly, in the rend case, hidden services probably do not want to expose their Layer3 (S) guards quite so easily to a client's chosen Rendezvous Point, and again, the client probably does not want to use their Layer3 (S) guards as its Rendezvous point, to avoid visit linkability. This means we again have 8 hops for rends: C - L - M - S - R -- E - S - M - L - H Unfortunately, this is starting to get ridiculous. While there are clear security benefits here, I think 8 hops is definitely at the point where we can forget about voice and other interactive traffic behaving reasonably. So what could we cut, if we wanted to? Well, going back to the Prop247 threat model, we want the adversary to perform at least two attacks: a Sybil and one or mode node compromise attacks. So maybe we can (in some cases, or optionally?) eliminate the M nodes from the path. Since the linkability risks may be acceptable for some applications, maybe we can also optionally allow clients or servers to omit the ephemeral hop. This basically gives us three options for path lengths. Let's consider each path type: Hsdir post/fetch: 1. C - L - M - S - E - H 2. C - L - S - E - H 3. C - L - S - H Intro: 1. C - L - M - S - E -- I - S - M - L - H 2. C - L - S - E -- I - S - L - H *3. C - L - S -- I&S - L - H (* IP Intersection attack!) Rend: 1. C - L - M - S - R -- E - S - M - L - H 2. C - L - S - R -- E - S - L - H 3. C - L - R&S -- S - L - H Looking at these, we can see that we sacrifice the middle guards in the second option, which will come at the cost of one less compromise attack (but still the need to compromise the long-lived guard). We also lose the unlinkability in the third option, and this actually bites us in Intro 3: the hidden service L guard can perform a long-term intersection attack, watching for published intro points and matching that to the circuits that H makes to them. So that path length probably should not be used. But what about the others? Especially that Rend case? I really like the security properties of the full 8 hop paths, but it seems to me that for highly-interactive applications, we can provide the option for users to give up some of the unlinkability in exchange for that 4 hop circuit, which might actually allow for e2e hidden service voice and video to have a shot at working. Are there any risks with paths this short for that case? Does it make sense to provide users with these different path length and latency options? I'm thinking that the service could list its preferred path length in its hsdesc, and the client could override that as it chooses (either for more or less security). Is that dangerous? We were already considering letting users choose their guard set sizes. Why not path lengths also (or instead)? -- Mike Perry

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