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Prop#344: Prioritizing Protocol Information Leaks in Tor
by Mike Perry 23 Aug '23

23 Aug '23

As part of Sponsor 112, Tor has an objective to address covert channels that malicious relays can use to deanonymize users. This proposal lays the groundwork by categorizing these issues, and prioritizes them according to their severity. Subsequent proposals will deal with specific solutions. I am posting just the intro section of this proposal here. The full proposal is at: https://gitlab.torproject.org/tpo/core/torspec/-/blob/main/proposals/344-pr… Filename: 344-protocol-info-leaks.txt Title: Prioritizing Protocol Information Leaks in Tor Author: Mike Perry Created: 2023-07-17 Purpose: Normative Status: Open 0. Introduction Tor's protocol has numerous forms of information leaks, ranging from highly severe covert channels, to behavioral issues that have been useful in performing other attacks, to traffic analysis concerns. Historically, we have had difficulty determining the severity of these information leaks when they are considered in isolation. At a high level, many information leaks look similar, and all seem to be forms of traffic analysis, which is regarded as a difficult attack to perform due to Tor's distributed trust properties. However, some information leaks are indeed more severe than others: some can be used to remove Tor's distributed trust properties by providing a covert channel and using it to ensure that only colluding and communicating relays are present in a path, thus deanonymizing users. Some do not provide this capability, but can be combined with other info leak vectors to quickly yield Guard Discovery, and some only become dangerous once Guard Discovery or other anonymity set reduction is already achieved. By prioritizing information leak vectors by their co-factors, impact, and resulting consequences, we can see that these attack vectors are not all equivalent. Each vector of information leak also has a common solution, and some categories even share the same solution as other categories. This framework is essential for understanding the context in which we will be addressing information leaks, so that decisions and fixes can be understood properly. This framework is also essential for recognizing when new protocol changes might introduce information leaks or not, for gauging the severity of such information leaks, and for knowing what to do about them. Hence, we are including it in tor-spec, as a living, normative document to be updated with experience, and as external research progresses. It is essential reading material for any developers working on new Tor implementations, be they Arti, Arti-relay, or a third party implementation. This document is likely also useful to developers of Tor-like anonymity systems, of which there are now several, such as I2P, MASQUE, and Oxen. They definitely share at least some, and possibly even many of these issues. Readers who are relatively new to anonymity literature may wish to first consult the Glossary in Section 3, especially if terms such as Covert Channel, Path Bias, Guard Discovery, and False Positive/False Negative are unfamiliar or hazy. There is also a catalog of historical real-world attacks that are known to have been performed against Tor in Section 2, to help illustrate how information leaks have been used adversarially, in practice. We are interested in hearing from journalists and legal organizations who learn about court proceedings involving Tor. We became aware of three instances of real-world attacks covered in Section 2 in this way. Parallel construction (hiding the true source of evidence by inventing an alternate story for the court -- also known as lying) is a possibility in the US and elsewhere, but (so far) we are not aware of any direct evidence of this occurring with respect to Tor cases. Still, keep your eyes peeled... 0.1. Table of Contents 1. Info Leak Vectors 1.1. Highly Severe Covert Channel Vectors 1.1.1. Cryptographic Tagging 1.1.2. End-to-end cell header manipulation 1.1.3. Dropped cells 1.2. Info Leaks that enable other attacks 1.2.1. Handshakes with unique traffic patterns 1.2.2. Adversary-Induced Circuit Creation 1.2.3. Relay Bandwidth Lying 1.2.4. Metrics Leakage 1.2.5. Protocol Oracles 1.3. Info Leaks of Research Concern 1.3.1. Netflow Activity 1.3.2. Active Traffic Manipulation Covert Channels 1.3.3. Passive Application-Layer Traffic Patterns 1.3.4. Protocol or Application Linkability 1.3.5. Latency Measurement 2. Attack Examples 2.1. CMU Tagging Attack 2.2. Guard Discovery Attacks with Netflow Deanonymization 2.3. Netflow Anonymity Set Reduction 2.4. Application Layer Confirmation 3. Glossary The remainder of this proposal can be read at: https://gitlab.torproject.org/tpo/core/torspec/-/blob/main/proposals/344-pr… -- Mike Perry

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Calling Tor Volunteers and Developers! Help Shape the Future of Tor Relay Updates!
by Ravi Kumar 25 Jul '23

25 Jul '23

Dear Tor Volunteers and Developers, We are reaching out to you today to seek your invaluable expertise and insights in shaping the future of Tor relay updates. As part of an MSc Dissertation, a comprehensive study is underway to gain a deeper understanding of the significance of Tor relay updates from the unique perspective of developers like yourself. Your participation is pivotal to the success of this research, as we seek to explore your thoughts and opinions on a proposed automatic update mechanism for the relay. By lending your expertise, you will play a key role in advancing the health of the Tor network and enhancing the overall experience for millions of users around the globe. Rest assured that all your responses will be treated with the utmost care and confidentiality. To safeguard your data, the survey has been thoughtfully designed on an end-to-end encrypted platform, aligning with our commitment to ethical principles. We genuinely value your privacy and will handle your contributions with utmost respect and protection. We acknowledge the value of your time and effort, and we assure you that your input, which requires only 10 minutes, will wield a significant influence on the advancement of the Tor network. Don't miss out on this chance to contribute; the survey will remain open until August 5th. We invite you to join us today in shaping transformative research for Tor's bright future. Should you have any questions or require further information, please don't hesitate to contact us at S2450888(a)ed.ac.uk. We wholeheartedly welcome your feedback and queries, and your cooperation is genuinely appreciated. Together, we can make a meaningful difference and construct a stronger, more secure online world for everyone. Participate now and be an integral part of shaping the future of Tor relay updates through this link: https://cryptpad.fr/form/#/2/form/view/pb7wKm8zl0D62PsW93fz4wiW73i9nzDM-Jxc… [https://cryptpad.fr/customize/images/opengraph_preview/og-form.png]<https://cryptpad.fr/form/#/2/form/view/pb7wKm8zl0D62PsW93fz4wiW73i9nzDM-Jxc…> Encrypted Form<https://cryptpad.fr/form/#/2/form/view/pb7wKm8zl0D62PsW93fz4wiW73i9nzDM-Jxc…> CryptPad: end-to-end encrypted collaboration suite cryptpad.fr Thank you for your essential role in this important journey. Best regards, Ravi Kumar S2450888(a)ed.ac.uk The University of Edinburgh is a charitable body, registered in Scotland, with registration number SC005336. Is e buidheann carthannais a th' ann an Oilthigh Dhùn Èideann, clàraichte an Alba, àireamh clàraidh SC005336.

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Network Health team and analysis work
by Georg Koppen 06 Jul '23

06 Jul '23

Hello everyone! The Network Health team is best known for its work in the bad-relays area and being concerned with providing metrics + keeping an eye on the health of the Tor network. While that involves doing analyses to answer our own questions it was not clear so far what we should do with questions about the network or available data which got raised by other teams (i.e. you). Should we do those analyses as well or should we just provide the necessary data and each team then tries to answer their questions by themselves? This got raised a bunch of times in the past[1][2] and I am happy to announce that the Network Health team is stepping up and helping you with your analyses, if desired. The idea would be that we'd do the analysis work in those cases, alone or together, and accumulate/improve a set of scripts and tools over time at a single place, so that both we and other interested parties can do those analyses faster and better in the long(er) run. The tools should be open so that other folks can help improving and shaping them according to their needs. We have a dedicated analysis project[3] where we track all analysis related issues and which contains tools and documentation about how to use them for our work. If there is any analysis work you would like us to get done, please file a ticket in that project. If you did a similar analysis in the past by yourself we'd love to hear about it as it might speed up our work and we could build documentation out of it and add available code to the analysis project. Additionally, please assume we are no experts in your area of work, but don't hesitate to file tickets because of that. We'll ask if things are unclear. :) To get your analysis questions answered in a timely manner it would greatly help if they were attached to some sponsored work as that makes it usually easier to justify picking them up among all the other things on our plate. Additionally, emergencies (like new blocking events in country X) should be easily justifiable as well, in particular as we have a "surprise 'anomaly analysis' on the network as needed"-item on our roadmap throughout the year. I plan to make sure that we have sufficient spare cycles available for that work should it be needed. If your desired analysis does not fall into either of those categories don't despair, we'll try to find a way to get it done nonetheless. Thanks, Georg P.S.: If you are not part of any of our teams but want to do an analysis by yourself or just note an analysis idea somewhere, feel free to start by filing a ticket in the analysis project as well. Others might just jump on it and get it done because they might be curious about the answers themselves. :) [1] https://gitlab.torproject.org/tpo/network-health/metrics/relay-search/-/iss… [2] https://gitlab.torproject.org/tpo/network-health/team/-/issues/250#note_286… [3] https://gitlab.torproject.org/tpo/network-health/analysis

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[Update] Network Status APIs
by Mattia Righetti 06 Jul '23

06 Jul '23

Greetings Tor devs, During the last two weeks there has been an improvement in the Network Status APIs[0]. Network Status APIs is going to replace Onionoo web protocol as the Network Health Team moves most of the current bridges and relays data from files stored on disk to Postgres and VictoriaMetrics. We now have an initial working version of the `/summary` and `/bandwidth` endpoint. The first endpoint already has some working filters, while the latter does not yet. In the upcoming weeks we plan to stabilize and test these endpoints while we continue the development of others. The project initially started and was setup to look like a Onionoo copy to prevent most clients from breaking and for a smoother transition to the new protocol. We are now in the process of redefining some responses as the Onionoo implementation introduces some limitations. In particular, changes will affect responses that contain timeseries data stored on VictoriaMetrics as we thought it made more sense to just return a direct ref to VictoriaMetrics[1] for those requests, this way a client can decide to fetch referenced data or not based on its needs. Please do reach out to me, hiro or GeKo if you have any ideas or feedback you'd like to share with us. Cheers, Matt [0]: https://gitlab.torproject.org/tpo/network-health/metrics/networkstatusapi/ [1]: https://gitlab.torproject.org/tpo/network-health/metrics/networkstatusapi/-…

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Network Status APIs
by Mattia Righetti 22 Jun '23

22 Jun '23

Greetings Tor devs, In an effort to improve current resource utilisation, the Network Health Status team is developing a new version of their pipeline [1]. Previously, much of the data was stored on files, this made many operations slow due to their I/O bound nature. The new pipeline will transfer much of the data related to Tor nodes and bridges from files stored on a single server's disk to two separate databases: Postgres and Victoria Metrics. With this new approach, there's the need to develop a new service that is going to replace the current onionoo web protocol [2]. The main objective of this project is to design a RESTful API service, using the actix_web framework, that is going to be integrated in the new pipeline v2.0 to support data retrieval of bridges and relays from the two databases and additionally provide new features such as historic data search. The project will be developed over the next few weeks as part of the GSoC sponsored program. Please do reach out to me, hiro or GeKo if you have any ideas or feedback you'd like to share with us. Cheers, Matt [1] https://gitlab.torproject.org/tpo/network-health/team/-/wikis/metrics/colle… [2] https://gitlab.torproject.org/tpo/network-health/metrics/networkstatusapi/

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Two features that would help load-balanced bridges
by David Fifield 01 Jun '23

01 Jun '23

After the blocking of Tor in Russia in December 2022, the number of Snowflake users rapidly increased. Eventually the tor process became the limiting factor for performance, using all of one CPU core. In a thread on tor-relays, we worked out a design where we run multiple instances of tor on the same host, all with the same identity keys, in order to effectively use all the server's CPU resources. It's running on the live bridge now, and as a result the bridge's bandwidth use has roughly doubled. Design thread https://forum.torproject.net/t/tor-relays-how-to-reduce-tor-cpu-load-on-a-s… Installation instructions https://gitlab.torproject.org/tpo/anti-censorship/team/-/wikis/Survival-Gui… Two details came up that are awkward to deal with. We have workaround for them, but they could benefit from support from core tor. They are: 1. Provide a way to disable onion key rotation, or configure a custom onion key. 2. Provide a way to set a specific authentication cookie for ExtORPort SAFE_COOKIE authentication, or a new authentication type that doesn't require credentials that change whenever tor is restarted. I should mention that, apart from the load-balancing design we settled on, we have brainstormed some other options for scaling the Snowflake bridge or bridges. At this point, none of these ideas can immediately be put into practice, because there's no way to tell tor "connect to one of these bridges at random, but only one," or "connect to this bridge, but accept any of these fingerprints." https://bugs.torproject.org/tpo/anti-censorship/pluggable-transports/snowfl… # Disable onion key rotation Multiple tor instances with the same identity keys will work fine for the first 5 weeks (onion-key-rotation-days + onion-key-grace-period-days), but after that time the instances will have independently rotated their onion keys, and clients will have connection failures unless the load balancer happens to connect them to the instance whose descriptor they have cached. This post investigates what the failure looks like: https://lists.torproject.org/pipermail/tor-relays/2022-January/020238.html Examples of what could work here are a torrc option to set onion-key-rotation-days to a large value, an option to disable onion key rotation, an option to set a certain named file as the onion key. What we are doing now is a bit of a nasty hack: we create a directory named secret_onion_key.old, so that a failed replace_file causes an early exit from rotate_onion_key. https://gitweb.torproject.org/tor.git/tree/src/feature/relay/router.c?h=tor… There are a few apparently benign side effects, like tor trying to rebuild its descriptor every hour, but it's effective at stopping onion key rotation. https://lists.torproject.org/pipermail/tor-relays/2022-January/020277.html # Stable ExtORPort authentication ExtORPort (extended ORPort) is a protocol that lets a pluggable transport attach transport and client IP metadata to a connection, for metrics purposes. In order to connect to the ExtORPort, the pluggable transport needs to authenticate using a scheme like ControlPort authentication. https://gitweb.torproject.org/torspec.git/tree/proposals/217-ext-orport-aut… tor generates a secret auth cookie and stores it in a file. When the pluggable transport process is managed by tor, tor tells the pluggable transport where to find the file by setting the TOR_PT_AUTH_COOKIE_FILE environment variable. In the load-balanced configuration, the pluggable transport server (snowflake-server) is not run and managed by tor. It is an independent daemon, so it doesn't have access to TOR_PT_AUTH_COOKIE_FILE (which anyway would be a different path for every tor instance). The bigger problem is that tor regenerates the auth cookie and rewrites the file on every restart. All the tor instances have different cookies, and snowflake-server does not know which it will get through the load balancer, so it doesn't know what cookie to use. Examples of what would work here are an option to use a certain file as the auth cookie, an option to leave the auth cookie file alone if it already exists, or a new ExtORPort authentication type that can use the same credentials across multiple instances. What we're doing now is using a shim program, extor-static-cookie, which presents an ExtORPort interface with a static auth cookie for snowflake-server to authenticate with, then re-authenticates to the ExtORPort of its respective instance of tor, using that instance's auth cookie. https://lists.torproject.org/pipermail/tor-relays/2022-January/020183.html

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txtorcon v23.5.0
by meejah 19 May '23

19 May '23

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA512 I'm happy to announce txtorcon 23.5.0 with the following changes: * twisted.web.client.Agent instances now use the same HTTPS policy by default as twisted.web.client.Agent. It is possible to override this policy with the tls_context_factory= argument, the equivalent to Agent's contextFactory= (Thanks to Itamar Turner-Trauring) * Added support + testing for Python 3.11. * No more ipaddress dependency You can download the release from PyPI or GitHub (or of course "pip install txtorcon"): https://pypi.python.org/pypi/txtorcon/23.5.0 https://github.com/meejah/txtorcon/releases/tag/v23.5.0 Releases are also available from the hidden service: http://fjblvrw2jrxnhtg67qpbzi45r7ofojaoo3orzykesly2j3c2m3htapid.onion/txtor… http://fjblvrw2jrxnhtg67qpbzi45r7ofojaoo3orzykesly2j3c2m3htapid.onion/txtor… You can verify the sha256sum of both by running the following 4 lines in a shell wherever you have the files downloaded: cat <<EOF | sha256sum --check 93fd80a9dd505f698d0864fe93db8b6a9c1144b5feb91530820b70ed8982651c dist/txtorcon-23.5.0.tar.gz 987f0a91184f98cc3f0a7eccaa42f5054063744d6ac15e325cfa666403214208 dist/txtorcon-23.5.0-py3-none-any.whl EOF thanks, meejah -----BEGIN PGP SIGNATURE----- iQFFBAEBCgAvFiEEnVor1WiOy4id680/wmAoAxKAaacFAmRm0DoRHG1lZWphaEBt ZWVqYWguY2EACgkQwmAoAxKAaae/+wgAw3gAm65npc7+yMdGFixNmCd+RUXorJq9 Hy76hK3BWdtNIA6TZF20QFYs3CX5Vepa0vCJOK1N40fYgxoZTb1/828Zp6Zq2+Gn piJGvQ0Z1S95ww7lwSV77o67Xf7PozhLR+k7DaOdY8ugvLb/0Rdp15BykF5DWIo8 PRgqB8uZ418ebmDLLrYtqYTdlcUMxFTji4CHXc4N55/2hVHiFiuFt59os6kJ3iG1 u90lmQH8vbDyVF7N6tpgEAdWeb7OdgDbtzhVBdBWHrPg+vDO+UL7WZU8ZjDAcdEr YzzmK3fIiCH7ngG2E/VIebiJfrjAA9G4eZXltIm7VcWh5css9MXY1Q== =TeQp -----END PGP SIGNATURE-----

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Hacks to reduce Tor's initial download on slow Internet, sacrificing privacy?
by Holmes Wilson 08 May '23

08 May '23

Hi everyone, Is there a way right now to get Tor hidden service functionality (hosting a hidden service, connecting to hidden services) on a connection where the Internet is so slow and unreliable that the initial download of network information currently takes ~forever, provided one is willing to sacrifice metadata protection? Is there a way to download, say, 100x less network information on startup and still effectively host and connect to hidden services? Or is there a way to hardcode network information with the client, since that can be installed before going into the slow Internet zone, from a CDN that is less impacted, or from a source on the local network? (I read that this is how Tor worked in the past?) The context is the following: I have a p2p messaging app that uses Tor and hidden services (Quiet) in a way similar to Ricochet or Onionshare. I'm going to a conference where last year the Internet was so slow that Tor's initial download of network information took too long and kept timing out, rendering Quiet unusable. The Internet was, however, fairly reliable and usable for e.g. web browsing and messaging. I'd like to be able to use Quiet at this conference. It would be used purely as a demo for a few days, and we could warn everyone that our use of Tor did not offer its typical security properties. (Then in future years we might support p2p connectivity over local wifi, like Briar does!) My understanding is that the network information download step is to protect users against epistemic attacks. My intuition is that for situations where this doesn't matter there is some way to use Tor with a small subset of the network information and that the initial download could be skipped. Is this true? What's the best way to do it in the Tor client we ship? (I'm familiar with the Walking Onions paper, but looking for something that is ready now. There isn't already an implementation of Walking Onions, is there?) Thanks! Holmes

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New Proposal - CAA Extensions for the Tor Rendezvous Specification
by Q Misell 08 May '23

08 May '23

Hi all, I've spent some time working on ACME for Tor hidden services (you may have seen discussion of this work on the onion-advisors mailing list). Full details of the project are available at https://e.as207960.net/w4bdyj/AX8Ffqsd Attached is my proposal for a change to the Tor Rendezvous Specification to support the inclusion of CAA records in hidden service descriptors. My fork of Tor implementing publishing these records is available at https://e.as207960.net/w4bdyj/XMN03dmD Thanks, Q ------------------------------ Any statements contained in this email are personal to the author and are not necessarily the statements of the company unless specifically stated. AS207960 Cyfyngedig, having a registered office at 13 Pen-y-lan Terrace, Caerdydd, Cymru, CF23 9EU, trading as Glauca Digital, is a company registered in Wales under № 12417574 <https://find-and-update.company-information.service.gov.uk/company/12417574>. ICO register №: ZA782876 <https://ico.org.uk/ESDWebPages/Entry/ZA782876>. UK VAT №: GB378323867. EU VAT №: EU372013983. Turkish VAT №: 0861333524. South Korean VAT №: 522-80-03080. Glauca Digital and the Glauca logo are registered trademarks in the UK, under № UK00003718474 and № UK00003718468, respectively.

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Suggestions for Arti Example Programs
by Saksham Mittal 08 May '23

08 May '23

Hello there! I was recently selected as a GSoC contributor to help improve Arti by providing example utilities to test drive the APIs. I've come up with a couple ideas in my GSoC proposal and I wanted to share them as well as ask the community if they had any ideas of what projects they may want to see included in examples to help developers use Arti APIs in the future. 1. A download manager in Rust which will download the Tor Browser Bundle through a bridge connection. 2. A simple DNS lookup tool like dig which uses Tor relay to resolve hostnames anonymously, reducing the need to trust a DNS server. (This will use DNS over TLS) 3. A small script to just print out the current connection info on the circuit that had been chosen (like in Tor Browser) and to test relay and bridge connectivity at the user’s end for diagnostic purposes. 4. A bridge reachability monitor using Arti. This tool would hold connections to many obfs4 bridges open and detect when one of them goes down. (More info about this can be found at https://gitlab.torproject.org/tpo/core/arti/-/issues/717) 5. A small proxy server and client which uses just the pluggable transport code to create obfuscated connection between the two (doesn't go through the Tor network, it is just intended to showcase how to setup connections through PTs) I'd be happy to know of any cool ideas you may have to build with Arti that I could work on this summer! Thanks! -Saksham

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