tor-dev September 2018

tor-dev@lists.torproject.org

27 participants
23 discussions

the consequences of deprecating debian alpha repos with every new major branch
by nusenu 21 Dec '21

21 Dec '21

Hi, tldr: - more outdated relays (that is a claim I'm making and you could easily proof me wrong by recreating the 0.3.3.x alpha repos and ship 0.3.3.7 in them and see how things evolve after a week or so) - more work for the tpo website maintainer - less happy relay operators [3][4] - more work for repo maintainers? (since a new repo needs to be created) When the tor 0.3.4 alpha repos (deb.torproject.org) first appeared on 2018-05-23 I was about to submit a PR for the website to include it in the sources.list generator [1] on tpo but didn't do it because I wanted to wait for a previous PR to be merged first. The outstanding PR got merged eventually (2018-06-28) but I still did not submit a PR to update the repo generator for 0.3.4.x nonetheless and here is why. Recently I was wondering why are there so many relays running tor version 0.3.3.5-rc? (see OrNetStats or Relay Search) (> 3.2% CW fraction) Then I realized that this was the last version the tor-experimental-0.3.3.x-* repos were shipping before they got abandoned due to the new 0.3.4.x-* repos (I can no longer verify it since they got removed by now). Peter made it clear in the past that the current way to have per-major-version debian alpha repos (i.e. tor-experimental-0.3.4.x-jessie) will not change [2]: > If you can't be bothered to change your sources.list once or twice a > year, then you probably should be running stable. but maybe someone else would be willing to invoke a "ln" commands everytime a new new alpha repo is born. tor-alpha-jessie -> tor-experimental-0.3.4.x-jessie once 0.3.5.x repos are created the link would point to tor-alpha-jessie -> tor-experimental-0.3.5.x-jessie It is my opinion that this will help reduce the amount of relays running outdated versions of tor. It will certainly avoid having to update the tpo website, which isn't a big task and could probably be automated but it isn't done currently. "..but that would cause relay operators to jump from i.e. 0.3.3.x to 0.3.4.x alphas (and break setups)!" Yes, and I think that is better than relays stuck on an older version because the former repo no longer exists and operators still can choose the old repos which will not jump to newer major versions. [1] https://www.torproject.org/docs/debian.html.en#ubuntu [2] https://trac.torproject.org/projects/tor/ticket/14997#comment:3 [3] https://lists.torproject.org/pipermail/tor-relays/2018-June/015549.html [4] https://trac.torproject.org/projects/tor/ticket/26474 -- https://twitter.com/nusenu_ https://mastodon.social/@nusenu

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DNS-over-HTTPS (DOH) in Firefox/Torbrowser
by nusenu 01 Jul '20

01 Jul '20

Hi, since Mozilla did tests [0] on DOH [1] in Firefox I was wondering if Torbrowser developers have put any thought into that as well? Note: I'm _not_ suggesting to use DOH in torbrowser I'm just asking because the answer probably matters for exit documentation in the relay guide if clients do DNS themselves over TCP connections instead of relying on the exit (even if torbrowser is not the only tor client). thanks, nusenu [0] https://www.ghacks.net/2018/03/20/firefox-dns-over-https-and-a-worrying-shi… [1] https://datatracker.ietf.org/doc/draft-hoffman-dns-over-https/ -- https://mastodon.social/@nusenu twitter: @nusenu_

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Lets give every circuit its own exit IP?
by nusenu 18 Mar '20

18 Mar '20

The unbearable situation with Google's reCAPTCHA motivated this email (but it is not limited to this specific case). This idea came up when seeing a similar functionality in unbound (which has it for a different reason). Assumption: There are systems that block some tor exit IP addresses (most likely the bigger once), but they are not blocked due to the fact that they are tor exits. It just occurred that the IP got flagged because of "automated / malicious" requests and IP reputation systems. What if every circuit had its "own" IP address at the exit relay to avoid causing collateral damage to all users of the exit if one was bad? (until the exit runs out of IPs and starts to recycle previously used IPs again) The goal is to avoid accumulating a bad "reputation" for the single used exit IP address that affects all tor users of that exit. Instead of doing it on the circuit level you could do it based on time. Change the exit IP every 5 minutes (but do _not_ change the exit IPs for _existing_ circuits even if they live longer than 5 minutes). Yes, no one has that many IPv4 addresses but with the increasing availability of IPv6 at exits and destinations, this could be feasible to a certain extend, depending on how many IPv6 addresses the exit operator has. There are exit operators that have entire /48 IPv6 blocks. problems: - will not solve anything since reputation will shift to netblocks as well (How big of a netblock are you willing to block?) - you can tell two tor users easily apart from each other even if they use the same exit (or more generally: you can tell circuits apart). There might be all kinds of bad implications that I'm not thinking off right now. - check.tpo would no longer be feasible - how can do we still provide the list of exit IPs for easy blocking? Exits could signal their used netblock via their descriptor. What if they don't? (that in turn opens new kinds of attacks where an exit claims to be /0 and the target effectively blocks everything) - more state to track and store at the exit -... some random thoughts, nusenu -- https://mastodon.social/@nusenu twitter: @nusenu_

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Bandwidth scanner: request for feedback
by teor 20 Nov '18

20 Nov '18

Hi, Juga and pastly have been working hard on sbws. Sbws' results are now similar to torflow's results: https://trac.torproject.org/projects/tor/attachment/ticket/27135/20180826_0… Now that sbws is close to torflow, we want some feedback on its design. We’ll work on the design at the tor meeting in September. Please feel free to give feedback by email, or on the tickets: What happens when sbws doesn't match torflow? https://trac.torproject.org/projects/tor/ticket/27339 We suggest this rule: If an sbws deployment is within X% of an existing bandwidth authority, sbws is ok. (The total consensus weights of the existing bandwidth authorities are within 25% - 50% of each other, see #25459.) How long should sbws keep relay bandwidths? https://trac.torproject.org/projects/tor/ticket/27338 Torflow uses the latest self-reported relay observed bandwidth and bandwidth rate. Torflow uses a complex feedback loop for measured bandwidths. We think sbws can use a simple average or exponentially decaying weighted average. How should we scale sbws consensus weights? https://trac.torproject.org/projects/tor/ticket/27340 If sbws' total consensus weight is different to torflow's total consensus weight, how should we scale sbws? (The weights might differ because the measurement method is different, or because scanners and servers are in different locations.) In the bandwidth file spec, we suggest linear scaling. How should we round sbws consensus weights? https://trac.torproject.org/projects/tor/ticket/27337 Torflow currently rounds to 3 significant figures (which is a maximum of 0.5%). But I suggest 2 significant figures for sbws (or max 5%), because: - tor has a daily usage cycle that varies by 10% - 20% - existing bandwidth authorities vary by 25% - 50% Proposal 276 contains a slightly more complicated rounding algorithm, which we may want to implement in sbws or in tor: https://gitweb.torproject.org/torspec.git/tree/proposals/276-lower-bw-granu… Does sbws need a maximum consensus weight fraction? https://trac.torproject.org/projects/tor/ticket/27336 Torflow uses 5%, but I suggest 1%, because the largest relay right now is only 0.5%. T -- teor Please reply @torproject.org New subkeys 1 July 2018 PGP C855 6CED 5D90 A0C5 29F6 4D43 450C BA7F 968F 094B ----------------------------------------------------------------------

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UX improvement proposal: Onion auto-redirects using Alt-Svc HTTP header
by George Kadianakis 26 Oct '18

26 Oct '18

UX improvement proposal: Onion auto-redirects using Alt-Svc HTTP header ======================================================================== 1. Motivation: Lots of high-profile websites have onion addresses these days (e.g. Tor , NYT, blockchain, ProPublica). All those websites seem confused on what's the right way to inform their users about their onion addresses. Here are some confusion examples: a) torproject.org does not even advertise their onion address to Tor users (!!!) b) blockchain.info throws an ugly ASCII page to Tor users mentioning their onion address and completely wrecking the UX (loses URL params, etc.) c) ProPublica has a "Browse via Tor" section which redirects to the onion site. Ideally there would be a consistent way for websites to inform their users about their onion counterpart. This would provide the following positives: + Tor users would use onions more often. That's important for user education and user perception, and also to partially dispell the darkweb myth. + Website operators wouldn't have to come up with ad-hoc ways to advertise their onion services, which sometimes results in complete breakage of the user experience (particularly with blockchain) This proposal specifies a simple way forward here that's far from perfect, but can still provide benefits and also improve user-education around onions so that in the future we could employ more advanced techniques. Also see Tor ticket #21952 for more discussion on this: https://trac.torproject.org/projects/tor/ticket/21952 2. Proposal Websites use the Alt-Svc HTTP header to specify their onion counterpart: http://httpwg.org/http-extensions/alt-svc.html The Tor Browser intercepts that header (if any) and auto-redirects the user to the onion site. Tor Browser only does so if the header is served over HTTPS. (That's it.) 3. Improvements 3.1. User education through notifications To minimize the probability of users freaking out about auto-redirects Tor Browser could inform the user that the auto-redirect is happening. This could happen with a small notification bar [*] below the URL bar informing users that "Tor Browser is auto-redirecting you to the secure onion site". The notification bar could also have a question mark button that provides the user with additional information on the merits of onion sites and why they should like them. [*]: like this one: http://www.topdreamweaverextensions.com/UserFiles/Image/firefox-bar.jpg 3.2. Auto-redirects too intrusive? Make them optional. If we think that auto redirects are too intrusive, we should consider making them optional, or letting the website specify the desired behavior. If a website wants to specify an onion address but doesn't like auto-redirects, it could specify that as part of Alt-Svc and we could still inform the user that an onion is available using a notification bar again. 4. Drawbacks This proposal is far from the perfect solution of course. Here are a few reasons why: 4.1. Auto-redirects are scary Novice users or paranoid users might freak out with auto-redirects since it's unexpected. They might think they are under attack or they got hacked. An argument against that is that we are already using HTTPS-everywhere which is basically a redirection layer, and while its redirection technique is simpler, sometimes the derivative URL is not similar to the original URL, and we still don't see people freaking out. I think that's because people trust Tor Browser to do the right thing. Combining this knowledge with section 3.1 might solve this problem. 4.2. No security/performance benefits While we could come up with auto-redirect proposals that provide security and performance benefits, this proposal does not actually provide any of those. As a matter of fact, the security remains the same as connecting to normal websites (since we trust its HTTP headers), and the performance gets worse since we first need to connect to the website, get its headers, and then also connect to the onion. Still _all_ the website approaches mentioned in the "Motivation" section suffer from the above drawbacks, and sysadmins still come up with ad-hoc ways to inform users abou their onions. So this simple proposal will still help those websites and also pave the way forward for future auto-redirect techniques. 4.3. Alt-Svc does not do exactly what we want I read in a blog post [*] that using Alt-Svc header "doesn’t change the URL in the location bar, document.location or any other indication of where the resource is; this is a “layer below” the URL.". IIUC, this is not exactly what we want because users will not notice the onion address, they will not get the user education part of the proposal and their connection will still be slowed down. I think we could perhaps change this in Tor Browser so that it rewrites the onion address to make it clear to people that they are now surfing the onionspace. [*]: https://www.mnot.net/blog/2016/03/09/alt-svc 5. The future As I said this is just a simple proposal to introduce the auto-redirect concept to people, and also to help some sysadmins who are currently coming up with weird ways to inform people about their onions. It's not the best way to do this, but it's definitely one of the simplest ways. In the future we could implement with more advanced auto-redirect proposals like: a) Have a "domains to onions" map into HTTPS-everywhere and have it do the autoredirects for us (performance benefits, and security benefits under many threat models). b) Bake onion addresses into SSL certificates and Let's Encrypt as suggested by comment:42 in #21952. But both of the designs above require non-trivial engineering/policy work and would still confuse people. So I think starting with a simple approach that will educate users and then moving to more advanced designs is a more normative way to go. ====================================================================== Let me know what you think :) (Should this be part of torspec?)

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Domain Fronting, Meek, Cloudflare, and Encrypted SNI...
by Nathaniel Suchy 23 Oct '18

23 Oct '18

Hi everyone, Cloudflare has added support to TLS 1.3 for encrypted server name indication (SNI). This mailing list post is a high level overview of how meek could take advantage of this in relation to Cloudflare who until just now wasn’t an option for domain fronting. What this means: Effectively domain fronting works by sending a different SNI and host header. CDN providers like Cloudflare started double checking to make governments happy, scratch that line, I mean to protect their customers from fraud and abuse. They seem to of backtracked now. Encrypted SNI means that a firewall or coffee shop owner won’t be able to use SNI to see the real origin of TLS traffic. Why this matters: With the right adjustments for TLS 1.3 and Encrypted SNI support, Cloudflare may be a viable option for Meek. Risks: * Firewall products could always use DPI and block TLS 1.3 altogether. * Firewall products could block all requests with encrypted SNI. Thoughts anyone? References: * https://blog.cloudflare.com/encrypted-sni/ * https://blog.cloudflare.com/esni

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Temporary hidden services
by Michael Rogers 22 Oct '18

22 Oct '18

Hi all, The Briar team is working on a way for users to add each other as contacts by exchanging links without having to meet in person. We don't want to include the address of the user's long-term Tor hidden service in the link, as we assume the link may be observed by an adversary, who would then be able to use the availability of the hidden service to tell whether the user was online at any future time. We're considering two solutions to this issue. The first is to use a temporary hidden service that's discarded after, say, 24 hours. The address of the temporary hidden service is included in the link. This limits the window during which the user's activity is exposed to an adversary who observes the link, but it also requires the contact to use the link before it expires. The second solution is to include an ECDH public key in the link, exchange links with the contact, and derive a hidden service key pair from the shared secret. The key pair is known to both the user and the contact. One of them publishes the hidden service, the other connects to it. They exchange long-term hidden service addresses via the temporary hidden service, which is then discarded. The advantage of the second solution is that the user's link is static - it doesn't expire and can be shared with any number of contacts. A different shared secret, and thus a different temporary hidden service, is used for adding each contact. But using a hidden service in such a way that the client connecting to the service knows the service's private key is clearly a departure from the normal way of doing things. So before pursuing this idea I wanted to check whether it's safe, in the sense that the hidden service still conceals its owner's identity from the client. Attacks against the availability of the service (such as uploading a different descriptor) are pointless in this scenario because the client is the only one who would connect to the service anyway. So I'm just interested in attacks against anonymity. Can anyone shed any light on this question? Or is this way of using hidden services too disgusting to even discuss? :-) Thanks, Michael

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Information on the handling of relays churn
by Adrien Luxey 28 Sep '18

28 Sep '18

Dear Tor developers, As a PhD student in distributed systems, I am studying onion routing. We would like to investigate an onion routing system that would run on users devices, i.e. a lot of nodes with crappy bandwidth and intermittent connection. To compare against Tor, I have been looking for information about how you currently handle the disconnection of relays, but I found no "digest" on the Web. Your code seems to point to the direction of core/or/circuit*, that I need to investigate further. I still would love some first-hand high-level description from you guys. I have the following questions: * When an OR disconnects while supporting active circuits, how is the failure detected? * How are the paths subsequently rebuilt? * To which extent would you say that Tor is resilient to churn? What would be the effects of a massive churn of relays? Where would be the bottleneck? If you have any questions on my work, I will be pleased to answer (though a little ashamed, because I know our system will never hold your security properties so tight)! With much respect for your work and philosophy, Adrien Luxey

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txtorcon 18.1.0
by meejah 27 Sep '18

27 Sep '18

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 I'm very pleased to announce txtorcon 18.1.0. This adds or fixes the following: * better error-reporting (include REASON and REMOTE_REASON if available) when circuit-builds fail (thanks David Stainton) * more-robust detection of "do we have Python3" (thanks Balint Reczey) * fix parsing of Unix-sockets for SOCKS * better handling of concurrent Web agent requests before SOCKS ports are known * allow fowarding to ip:port pairs for Onion services when using the "list of 2-tuples" method of specifying the remote vs local connections. You can download the release from PyPI or GitHub (or of course "pip install txtorcon"): https://pypi.python.org/pypi/txtorcon/18.1.0 https://github.com/meejah/txtorcon/releases/tag/v18.1.0 Releases are also available from the hidden service: http://timaq4ygg2iegci7.onion/txtorcon-18.1.0.tar.gz http://timaq4ygg2iegci7.onion/txtorcon-18.1.0.tar.gz.asc Or via a "version 3" 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 b61cf175a5f1d4092609caf05d178fcdcabf513928eec98d38125c501afea43c dist/txtorcon-18.1.0.tar.gz 98aba4a96c355c55ee5d8290b67a09380b02e1044fb2e76737f47f5a33659dce dist/txtorcon-18.1.0-py2.py3-none-any.whl EOF thanks, meejah -----BEGIN PGP SIGNATURE----- iQFFBAEBCAAvFiEEnVor1WiOy4id680/wmAoAxKAaacFAlusMDQRHG1lZWphaEBt ZWVqYWguY2EACgkQwmAoAxKAaadz3wgAk+UbYuw0lIwEqQZbhQ6oTk0cTu5GrB5q WkSbqPkj5Ph+y1iYMQoEgAZdD97zjpfGR+/JcyXbPyh4ZDcqkL8Hhay9yF2/PAkd agu1LBuBjVXOFvcw3D8Xi91miFwjmMKznAuR1Jv9gp66emw3qbZRZE9g1S9o1lCX 3Cx6o3kLiq8h7UmOiqFfCFGjNBFsaiDqf35P7FH7Btg4FYIGtI5/uQ3qgDtyqlhD YKA91KxZQoZFGiAhp5h84WXrvtuQ5tDjRNiIfh76xRFiFRnWe9ofELidKqEgnyzF shBqdGpaIT0g0NTQRhCnzBM7m3u0RHxkRblJWBLa6t4KYNFTMJ8Pag== =z+Lo -----END PGP SIGNATURE-----

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[release] Tor Metrics Library 2.5.0 and Tor Metrics Website 1.2.0
by Karsten Loesing 26 Sep '18

26 Sep '18

Hi, we just released new versions of the Tor Metrics Library, metrics-lib 2.5.0, and Tor Metrics Website, metrics-web 1.2.0. The primary reason for these new releases is that libraries contained in the tarball match the ones needed to build current master. Downloads are available at: https://dist.torproject.org/metrics-lib/2.5.0/ https://dist.torproject.org/metrics-web/1.2.0/ Please direct comments and questions to the metrics-team mailing list: https://lists.torproject.org/cgi-bin/mailman/listinfo/metrics-team All the best, Karsten -- on behalf of the Metrics Team.

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tor-dev September 2018