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The Tor Project
Dedham, MA
givvers: jason, emerssso + 4 others

Tor is free software and an open network that helps you defend against a form of network surveillance that threatens personal freedom and privacy, confidential business activities and relationships, and state security known as traffic analysis.

The Tor Project is a 501(c)3 organization.

Latest News

Aug 29, 2014

Looking for a way to help the Internet stay open and free? This topic needs some dedicated people to give it more attention — it could easily grow to as large a project as Tor itself. In the short term, OTF's Information Controls Fellowship Program has expressed interest in funding somebody to get this project going, and EFF's Eva Galperin has said she'd be happy to manage the person as an OTF fellow at EFF, with mentorship from Tor people. The first round of those proposals has a deadline in a few days, but if that timeframe doesn't work for you, this problem isn't going away: let us know and we can work with you to help you coordinate other funding.

The problem

We used to think there are two main ways that the Tor network can fail. First, legal or policy pressure can make it so nobody is willing to run a relay. Second, pressure on or from Internet Service Providers can reduce the number of places willing to host exit relays, which in turn squeezes down the anonymity that the network can provide. Both of these threats are hard to solve, but they are challenges that we've known about for a decade, and due in large part to strong ongoing collaborations we have a pretty good handle on them.

We missed a third threat to Tor's success: a growing number of websites treat users from anonymity services differently. Slashdot doesn't let you post comments over Tor, Wikipedia won't let you edit over Tor, and Google sometimes gives you a captcha when you try to search (depending on what other activity they've seen from that exit relay lately). Some sites like Yelp go further and refuse to even serve pages to Tor users.

The result is that the Internet as we know it is siloing. Each website operator works by itself to figure out how to handle anonymous users, and generally neither side is happy with the solution. The problem isn't limited to just Tor users, since these websites face basically the same issue with users from open proxies, users from AOL, users from Africa, etc.

Two recent trends make the problem more urgent. First, sites like Cloudflare, Akamai, and Disqus create bottlenecks where their components are used by many websites. This centralization impacts many websites at once when e.g. Cloudflare changes its strategy for how to handle Tor users. Second, services increasingly outsource their blacklisting, such that e.g. Skype refuses connections from IP addresses that run Tor exit relays, not because they worry about abuse via Tor (it's hard to use Skype over Tor), but because their blacklist provider has an incentive to be overbroad in its blocking. (Blacklist providers compete in part by having "the most complete" list, and in many cases it's hard for services to notice that they're losing contributions from now-missing users.)

Technical mechanisms do exist to let anonymous users interact with websites in ways that control abuse better. Simple technical approaches include "you can read but you can't post" or "you have to log in to post". More complex approaches track reputation of users and give them access to site features based on past behavior of the user rather than on past behavior of their network address. Several research designs suggest using anonymous credentials, where users anonymously receive a cryptographic credential and then prove to the website that they possess a credential that hasn't been blacklisted — without revealing their credential, so the website can't link them to their past behavior.

Social mechanisms have also proven effective in some cases, ranging from community moderation (I hear Wikipedia Germany manually approves edits from users who don't have sufficiently reputable accounts), to flagging behavior from Tor users (even though you don't know *which* Tor user it is) so other participants can choose how to interact with them.

But applying these approaches to real-world websites has not gone well overall. Part of the challenge is that the success stories are not well-publicized, so each website feels like it's dealing with the question in isolation. Some sites do in fact face quite different problems, which require different solutions: Wikipedia doesn't want jerks to change the content of pages, whereas Yelp doesn't want competitors to scrape all its pages. We can also imagine that some companies, like ones that get their revenue from targeted advertising, are fundamentally uninterested in allowing anonymous users at all.

A way forward

The solution I envision is to get a person who is both technical and good at activism to focus on this topic. Step one is to enumerate the set of websites and other Internet services that handle Tor connections differently from normal connections, and look for patterns that help us identify the common (centralized) services that impact many sites. At the same time, we should make a list of solutions — technical and social — that are in use today. There are a few community-led starts on the Tor wiki already, like the DontBlockMe page and a List of Services Blocking Tor.

Step two is to sort the problem websites based on how amenable they would be to our help. Armed with the toolkit of options we found in step one, we should go to the first (most promising) site on the list and work with them to understand their problem. Ideally we can adapt one of the ideas from the toolkit; otherwise we'll need to invent and develop a new approach tailored to their situation and needs. Then we should go to the second site on the list with our (now bigger) toolkit, and so on down the list. Once we have some success stories, we can consider how to scale better, such as holding a conference where we invite the five best success cases plus the next five unsolved sites on our list.

A lot of the work will be building and maintaining social connections with engineers at the services, to help them understand what's possible and to track regressions (for example, every year or so Google gets a new engineer in charge of deciding when to give out Captchas, and they seem to have no institutional memory of how the previous one decided to handle Tor users). It might be that the centralization of Cloudflare et al can be turned around into an advantage, where making sure they have a good practices will scale to help many websites at once.

EFF is the perfect organization to lead this charge, given its community connections, its campaigns like Who has your back?, and its more (at least more than Tor ;) neutral perspective on the topic. And now, when everybody is sympathetic about the topic of surveillance, is a great time to try to take back some ground. We have a wide variety of people who want to help, from scientists and research groups who would help with technical solutions if only they understood the real problems these sites face, to users and activists who can help publicize both the successful cases and the not-yet-successful cases.

Looking ahead to the future, I'm also part of an upcoming research collaboration with Dan Boneh, Andrea Forte, Rachel Greenstadt, Ryan Henry, Benjamin Mako Hill, and Dan Wallach who will look both at the technical side of the problem (building more useful ideas for the toolkit) and also the social side of the problem: how can we quantify the loss to Wikipedia, and to society at large, from turning away anonymous contributors? Wikipedians say "we have to blacklist all these IP addresses because of trolls" and "Wikipedia is rotting because nobody wants to edit it anymore" in the same breath, and we believe these points are related. The group is at the "applying for an NSF grant" stage currently, so it will be a year or more before funding appears, but I mention it because we should get somebody to get the ball rolling now, and hopefully we can expect reinforcements to appear as momentum builds.

In summary, if this call to arms catches your eye, your next steps are to think about what you most want to work on to get started, and how you would go about doing it. You can apply for an OTF fellowship, or we can probably help you find other funding sources as needed too.

Aug 27, 2014

Welcome to the thirty-fourth issue of Tor Weekly News in 2014, the weekly newsletter that covers what is happening in the Tor community.

Orfox: a new Firefox-based secure browser for Android

With the growing popularity of pocket computers (also known as “phones”), users need to have access to censorship-circumvention and anonymity systems on these devices as well as on their desktop or laptop machines. While there is currently no supported implementation of Tor for Apple’s iOS, the Guardian Project works closely with the Tor Project to produce (amongst other software) a Tor client for Android named Orbot. Mobile applications can be proxied through Orbot just as they can through the Tor client on other operating systems, but mobile web browsing potentially suffers from the same issues that the Tor Browser was designed to protect against, such as disk leaks and a large attack surface. The Guardian Project has therefore also been maintaining a dedicated mobile browser for use with Orbot under the name Orweb.

Orweb is based on WebView, and is limited by that browser’s features; flaws such as the potential HTML5 IP leak, while possible to work around in the short term, have made it clear that the best future for secure mobile browsing lies in a switch to an application based on Firefox/Fennec/GeckoView.

Following a successful Google Summer of Code project by Amogh Pradeep and work by other Guardian Project members, Nathan Freitas announced that “a real working version” of Orfox, the new Orbot-compatible mobile browser, is now available. “All the necessary defaults [have been] changed to match Tor Browser’s defaults as closely as possible”; the developers also “remove the Android permissions for things like camera, mic, GPS” and “turn off webrtc.”

“We still need to figure out which preferences and features map between the desktop mobile browser and the Android version, so there is quite a bit of work to do”, but you can download and test this initial version by following the links in Nathan’s email. “Over the next few months we hope to launch this as our new official browser for Orbot, and deprecate Orweb as quickly as possible”, he concluded.

Miscellaneous news

A new release of ooniprobe, the network interference data collector for OONI, was announced by Arturo Filastò. Version 1.1.0 introduces a new command line tool “for listing the reports that have not been published to a collector and that allows the probe operator to choose which ones they would like to upload”. The new version also improves the privacy of the reports by sanitizing file paths.

Developers of applications using Onionoo — the web service to learn about currently running Tor relays and bridges — are invited to join the new onionoo-announce mailing list. Keeping the list low volume, Karsten Loesing plans on using it to announce major protocol changes, scheduled maintenance, major bug fixes, and other important news.

Yawning Angel has made available an experimental version of the Tor Browser that includes the latest version of the obfs4 pluggable transport. Testing on Windows and OS X would be particularly welcome.

Fabian Keil reported that FreeBSD now includes ports of liballium and obfsclient.

JusticeRage explained how relay operators who offer exiting on port 25 can protect the reputation of their domain name by using the Sender Policy Framework.

Sreenatha Bhatlapenumarthi sent the final GSoC report for the Tor Weather rewrite project. Juha Nurmi sent another report on the development of ahmia.fi.

Thanks to s7r for hosting a new mirror of the Tor Project’s website and software!

Tor help desk roundup

Users of different VPN (Virtual Private Network) services have told the help desk that Tor Browser has difficulty connecting to Tor when a VPN is in use. Using Tor with a VPN is not supported. For a trusted entry into the Tor network, bridges and pluggable transports are recommended, while for anonymizing all network traffic coming from a computer, Tails is recommended.

Easy development tasks to get involved with

The bandwidth authority scanners measure the actual bandwidth offered by Tor relays in order to get accurate information into the Tor consensus. The measurement process currently splits up the set of relays that are to be measured into 4 subsets, with the goal that measuring each of these subsets should take about the same time. However, this is not the case. Measuring subsets 2 and 3 is about twice as fast as measuring subset 1, and subset 4 is twice as fast as subset 2 and 3. If you're up for doing some experiments to split up the set into more equal subsets, please let us know about your findings on the ticket.


This issue of Tor Weekly News has been assembled by Lunar, harmony, Matt Pagan, Karsten Loesing, and dope457.

Want to continue reading TWN? Please help us create this newsletter. We still need more volunteers to watch the Tor community and report important news. Please see the project page, write down your name and subscribe to the team mailing list if you want to get involved!

Aug 20, 2014

Welcome to the thirty-third issue of Tor Weekly News in 2014, the weekly newsletter that covers what is happening in the community around Tor, Aphex Twin’s favorite anonymity network.

Tor Browser 3.6.4 and 4.0-alpha-1 are out

Erinn Clark took to the Tor Blog to announce two new releases by the Tor Browser team. The stable version (3.6.4) contains fixes for several new OpenSSL bugs, although since Tor should only be vulnerable to one of them, and “as this issue is only a DoS”, it is not considered a critical security update. This release also brings Tor Browser users the fixes that give log warnings about the RELAY_EARLY traffic confirmation attack explained last month. Please be sure to upgrade as soon as possible.

Alongside this stable release, the first alpha version of Tor Browser 4.0 is now available. Among the most exciting new features of this series is the inclusion of the meek pluggable transport. In contrast to the bridge-based transports already available in Tor Browser, meek relies on a principle of “too big to block”, as its creator David Fifield explained: “instead of going through a bridge with a secret address, you go through a known domain (www.google.com for example) that the censor will be reluctant to block. You don’t need to look up any bridge addresses before you get started”. meek currently supports two “front domains”, Google and Amazon Web Services; it may therefore be especially useful for users behind extremely restrictive national or local firewalls. David posted a fuller explanation of meek, and how to configure it, in a separate blog post.

This alpha release also “paves the way to [the] upcoming autoupdater by reorganizing the directory structure of the browser”, as Erinn wrote. This means that users upgrading from any previous Tor Browser series cannot extract the new version over their existing Tor Browser folder, or it will not work.

You can consult the full list of changes and bugfixes for both versions in Erinn’s post, and download the new releases themselves from the Tor website.

The Tor network no longer supports designating relays by name

Since the very first versions of Tor, relay operators have been able to specify “nicknames” for their relays. Such nicknames were initially meant to be unique across the network, and operators of directory authorities would manually “bind” a relay identity key after verifying the nickname. The process became formalized with the “Named” flag introduced in the 0.1.1 series, and later automated with the 0.2.0 series. If a relay held a unique nickname for long enough, the authoritywould recognize the binding, and subsequently reserve the name for half a year.

Nicknames are useful because it appears humans are not very good at thinking using long strings of random bits. Initially, they made it possible to understand what was happening in the network more easily, and to designate a specific relay in an abbreviated way. Having two relays in the network with the same nickname is not really problematic when one is looking at nodes, or a list in Globe, as relays can always be differentiated by their IP addresses or identity keys.

But complications arise when nicknames are used to specify one relay to the exclusion of another. If the wrong relay gets selected, it can become a security risk. Even though real efforts have been made to improve the situation, properly enforcing uniqueness has always been problematic, and a burden for the few directory authorities that handle naming.

Back in April, the “Heartbleed” bug forced many relays to switch to a new identity key, thus losing their “Named” flag. Because this meant that anyone designating relays by their nickname would now have a hard time continuing to do so, Sebastian Hahn decided to use the opportunity to get rid of the idea entirely.

This week, Sebastian wrote: “Code review down to 0.2.3.x has shown that the naming-related code hasn’t changed much at all, and no issues were found which would mean a Named-flag free consensus would cause any problems. gabelmoo and tor26 have stopped acting as Naming Directory Authorities, and — pending any issues — will stay that way.”

This means that although you can still give your relay a nickname in its configuration file, designating relays by nickname for any other purpose (such as telling Tor to avoid using certain nodes) has now stopped working. “If you — in your Tor configuration file — refer to any relay by name and not by identity hash, please change that immediately. Future versions of Tor will not support using names in the configuration at all”, warns Sebastian.

Miscellaneous news

meejah announced the release of version 0.11.0 of txtorcon, a Twisted-based Python controller library for Tor. This release brings several API improvements; see meejah’s message for full release notes and instructions on how to download it.

Mike Perry posted an overview of a recent report put together by iSEC Partners and commissioned by the Open Technology Fund to explore “current and future hardening options for the Tor Browser”. Among other things, Mike’s post addresses the report’s immediate hardening recommendations, latest thoughts on the proposed Tor Browser “security slider”, and longer-term security development measures, as well as ways in which the development of Google Chrome could inform Tor Browser’s own security engineering.

Nick Mathewson asked for comments on Trunnel, “a little tool to automatically generate binary encoding and parsing code based on C-like structure descriptions” intended to prevent “Heartbleed”-style vulnerabilities from creeping into Tor’s binary-parsing code in C. “My open questions are: Is this a good idea? Is it a good idea to use this in Tor? Are there any tricky bugs left in the generated code? What am I forgetting to think of?”, wrote Nick.

George Kadianakis followed up his journey to the core of what Tor does when trying to connect to entry guards in the absence of a network connection with another post running through some possible improvements to Tor’s behavior in these situations: “I’m looking forward to some feedback on the proposed algorithms as well as improvements and suggestions”.

Arturo Filastò requested feedback on some proposed changes to the format of the “test deck” used by ooni-probe, the main project of the Open Observatory of Network Interference. “A test deck is basically a way of telling it ‘Run this list of OONI tests with these inputs and by the way be sure you also set these options properly when doing so’…This new format is supposed to overcome some of the limitations of the old design and we hope that a major redesign will not be needed in the near future”, wrote Arturo.

Tor’s importance to users who are at risk, for a variety of reasons, makes it an attractive target for creators of malware, who distribute fake or modified versions of Tor software for malicious purposes. Following a recent report of a fake Tor Browser in circulation, Julien Voisin carried out an investigation of the compromised software, and posted a detailed analysis of the results. To ensure you are protected against this sort of attack, make sure you verify any Tor software you download before running it!

Arlo Breault submitted a status report for July.

As the annual Google Summer of Code season draws to a close, Tor’s GSoC students are submitting their final reports. Israel Leiva reported on the revamp of GetTor, Marc Juarez on the framework for website fingerprinting countermeasures, Juha Nurmi on ahmia.fi, Noah Rahman on Stegotorus enhancement, Amogh Pradeep on Orbot+Orfox, Daniel Martí on consensus diffs, Mikhail Belous on the multicore tor daemon work, Zack Mullaly on the secure ruleset updater for HTTPS Everywhere, and Quinn Jarrell on Fog, the pluggable transport combiner.

Tor help desk roundup

The help desk has been asked if it is possible to set up an anonymous blog using Tor. The Hyde project, developed by Karsten Loesing, documents the step-by-step process of using Tor, Jekyll, and Nginx to host an anonymous blog as a hidden service.

News from Tor StackExchange

The Tor StackExchange site is looking for another friendly and helpful moderator. Moderators need to take care of flagged items (spam, me-too comments, etc.), and are liaisons between the community and StackExchange’s community team. So, if you’re interested, have a look at the theory of moderation and post an answer to the question at the Tor StackExchange Meta site.


This issue of Tor Weekly News has been assembled by Lunar, harmony, David Fifield, qbi, Matt Pagan, Sebastian Hahn, Ximin Luo, and dope457.

Want to continue reading TWN? Please help us create this newsletter. We still need more volunteers to watch the Tor community and report important news. Please see the project page, write down your name and subscribe to the team mailing list if you want to get involved!

Aug 18, 2014

In May, the Open Technology Fund commissioned iSEC Partners to study current and future hardening options for the Tor Browser. The Open Technology Fund is the primary funder of Tor Browser development, and it commissions security analysis and review for all of the projects that it funds as a standard practice. We worked with iSEC to define the scope of the engagement to focus on the following six main areas:

  1. Review of the current state of hardening in Tor Browser
  2. Investigate additional hardening options and instrumentation
  3. Perform historical vulnerability analysis on Firefox, in order to make informed vulnerability surface reduction recommendations
  4. Investigate image, audio, and video codecs and their respective library's vulnerability history
  5. Review our current about:config settings, both for vulnerability surface reduction and security
  6. Review alternate/obscure protocol and application handlers


The complete report is available in the iSEC publications github repo. All tickets related to the report can be found using the tbb-isec-report keyword. General Tor Browser security tickets can be found using the tbb-security keyword.

Major Findings and Recommendations

The report had the following high-level findings and recommendations.

  • Address Space Layout Randomization is disabled on Windows and Mac

  • Due to our use of cross-compilation and non-standard toolchains in our reproducible build system, several hardening features have ended up disabled. We have known about the Windows issues prior to this report, and should have a fix for them soon. However, the MacOS issues are news to us, and appear to require that we build 64 bit versions of the Tor Browser for full support. The parent ticket for all basic hardening issues in Tor Browser is bug #10065.

  • Participate in Pwn2Own

  • iSEC recommended that we find a sponsor to fund a Pwn2Own reward for bugs specific to Tor Browser in a semi-hardened configuration. We are very interested in this idea and would love to talk with anyone willing to sponsor us in this competition, but we're not yet certain that our hardening options will have stabilized with enough lead time for the 2015 contest next March.

  • Test and recommend the Microsoft Enhanced Mitigation Experience Toolkit on Windows

  • The Microsoft Enhanced Mitigation Experience Toolkit is an optional toolkit that Windows users can run to further harden Tor Browser against exploitation. We've created bug #12820 for this analysis.

  • Replace the Firefox memory allocator (jemalloc) with ctmalloc/PartitionAlloc

  • PartitionAlloc is a memory allocator designed by Google specifically to mitigate common heap-based vulnerabilities by hardening free lists, creating partitioned allocation regions, and using guard pages to protect metadata and partitions. Its basic hardening features can be picked up by using it as a simple malloc replacement library (as ctmalloc). Bug #10281 tracks this work.

  • Make use of advanced ParitionAlloc features and other instrumentation to reduce the risk from use-after-free vulnerabilities

  • The iSEC vulnerability review found that the overwhelming majority of vulnerabilities to date in Firefox were use-after-free, followed closely by general heap corruption. In order to mitigate these vulnerabilities, we would need to make use of the heap partitioning features of PartitionAlloc to actually ensure that allocations are partitioned (for example, by using the existing tags from Firefox's about:memory). We will also investigate enabling assertions in limited areas of the codebase, such as the refcounting system, the JIT and the Javascript engine.

Vulnerability Surface Reduction (Security Slider)

A large portion of the report was also focused on analyzing historical Firefox vulnerability data and other sources of large vulnerability surface for a planned "Security Slider" UI in Tor Browser.

The Security Slider was first suggested by Roger Dingledine as a way to make it easy for users to trade off between functionality and security, gradually disabling features ranked by both vulnerability count and web prevalence/usability impact.

The report makes several recommendations along these lines, but a brief distillation can be found on the ticket for the slider.

At a high level, we plan for four levels in this slider. "Low" security will be the current Tor Browser settings, with the addition of JIT support. "Medium-Low" will disable most of the JIT, and make HTML5 media click-to-play via NoScript. "Medium-High" will disable the rest of the JIT, will disable JS on non-HTTPS url bar origins, and disable SVG. "High" will fully disable Javascript, block remote fonts via NoScript, and disable all media codecs except for WebM (which will remain click-to-play).

The Long Term

A web browser is a very large and complicated piece of software, and while we believe that the privacy properties of Tor Browser are better than those of every other web browser currently available, it is very important to us that we raise the bar to successful code execution and exploitation of Tor Browser as well.

We are very eager to see the deployment of sandboxing support in Firefox, which should go a long way to improving the security of Tor Browser as well. To improve security for their users, Mozilla has recently shifted 10 engineers into the Electrolysis project, which provides the groundwork for producing a multiprocess sandbox architecture for the desktop Firefox. This will allow them to provide a Google Chrome style security sandbox for website content, to reduce the risk from software vulnerabilities, and generally impede exploitability.

Until that time, we will also be investigating providing hardened builds of Tor Browser using the AddressSanitizer and Virtual Table Verification features of newer GCC releases. While this will not eliminate all vectors of memory corruption-based exploitation (in particular, the hardening properties of AddressSanitizer are not as good as those provided by SoftBounds+CETS for example, but that compiler is not yet production-ready), it should raise the bar to exploitation. We are hopeful that these builds in combination with PartitionAlloc and the Security Slider will satisfy the needs of our users who require high security and who are willing to trade performance and usability in order to get it.

We also hope to include optional application-wide sandboxes for Tor Browser as part of the official distribution.

Why not Google Chrome?

It is no secret that in many ways, both we and Mozilla are playing catch-up to reach the level of code execution security provided by Google Chrome, and in fact closely following the Google Chrome security team was one of the recommendations of the iSEC report.

In particular, Google Chrome benefits from a multiprocess sandboxing architecture, as well as several further hardening options and innovations (such as PartitionAlloc).

Unfortunately, our budget for the browser project is still very constrained compared to the amount of work that is required to provide the privacy properties we feel are important, and Firefox remains a far more cost-effective platform for us for several reasons. In particular, Firefox's flexible extension system, fully scriptable UI, solid proxy support, and its long Extended Support Release cycle all allow us to accomplish far more with fewer resources than we could with any other web browser.

Further, Google Chrome is far less amenable to supporting basic web privacy and Tor-critical features (such as solid proxy support) than Mozilla Firefox. Initial efforts to work with the Google Chrome team saw some success in terms of adding APIs that are crucial to addons such as HTTPS-Everywhere, but we ran into several roadblocks when it came to Tor-specific features and changes. In particular, several bugs required for basic proxy-safe Tor support for Google Chrome's Incognito Mode ended up blocked for various reasons. The worst offender on this front is the use of the Microsoft Windows CryptoAPI for certificate validation, without any alternative. This bug means that certificate revocation checking and intermediate certificate retrieval happen outside of the browser's proxy settings, and is subject to alteration by the OEM and/or the enterprise administrator. Worse, beyond the Tor proxy issues, the use of this OS certificate validation API means that the OEM and enterprise also have a simple entry point for installing their own root certificates to enable transparent HTTPS man-in-the-middle, with full browser validation and no user consent or awareness. All of this is not to mention the need for defenses against third party tracking and fingerprinting to prevent the linking of Tor activity to non-Tor usage, and which would also be useful for the wider non-Tor userbase.

While we'd love for this situation to change, and are open to working with Google to improve things, at present it means that our only option for Chrome is to maintain an even more invasive fork than our current Firefox patch set, with much less likelihood of a future merge than with Firefox. As a ballpark estimate, maintaining such a fork would require somewhere between 3 and 5 times the engineering staff and infrastructure we currently have at our disposal, in addition to the ramp-up time to port our current feature set over.

Unless either our funding situation or Google's attitude towards the features we require changes, Mozilla Firefox will remain the best platform for us to demonstrate that it is in fact possible to provide true privacy by design for the web for those who want it. It is very distressing that this means playing catch-up and forcing our users to make usability tradeoffs in exchange for improved browser security, but we will continue to do what we can to improve that situation, both with Mozilla and with our own independent efforts.

Aug 15, 2014

The recently released 4.0-alpha-1 version of Tor Browser includes meek, a new pluggable transport for censorship circumvention. meek tunnels your Tor traffic through HTTPS, and uses a technique called “domain fronting” to hide the fact that you are communicating with a Tor bridge—to the censor it looks like you are talking to some other web site. For more details, see the overview and the Child’s Garden of Pluggable Transports.

You only need meek if your Internet connection is censored so that you can’t use ordinary Tor. Even then, you should try other pluggable transports first, because they have less overhead. My recommended order for trying transports is:

  1. obfs3
  2. fte
  3. scramblesuit
  4. meek
  5. flashproxy

Use meek if other transports don’t work for you, or if you want to help development by testing it. I have been using meek for my day-to-day browsing for a few months now.

All pluggable transports have some overhead. You might find that meek feels slower than ordinary Tor. We’re working on some tickets that will make it faster in the future: #12428, #12778, #12857.

At this point, there are two different backends supported. meek-amazon makes it look like you are talking to an Amazon Web Services server (when you are actually talking to a Tor bridge), and meek-google makes it look like you are talking to the Google search page (when you are actually talking to a Tor bridge). It is likely that both will work for you. If one of them doesn’t work, try the other.

These instructions and screenshots are for the 4.0-alpha-1 release. If they change in future releases, they will be updated at https://trac.torproject.org/projects/tor/wiki/doc/meek#Quickstart.

How to use meek

First, download a meek-capable version of Tor Browser for your platform and language.

Verify the signature and run the bundle according to the instructions for Windows, OS X, or GNU/Linux.

On the first screen, where it says Which of the following best describes your situation?, click the Configure button.

Tor Network Settings “Which of the following best describes your situation?” screen with the “Configure” button highlighted.

On the screen that says Does this computer need to use a proxy to access the Internet?, say No unless you know you need to use a proxy. meek supports using an upstream proxy, but most users don’t need it.

Tor Network Settings “Does this computer need to use a proxy to access the Internet?” screen with “No” selected.

On the screen that says Does this computer's Internet connection go through a firewall that only allows connections to certain ports?, say No. As an HTTPS transport, meek only uses web ports, which are allowed by most firewalls.

Tor Network Settings “Does this computer's Internet connection go through a firewall that only allows connections to certain ports?” screen with “No” selected.

On the screen that says Does your Internet Service Provider (ISP) block or otherwise censor connections to the Tor Network?, say Yes. Saying Yes will lead you to the screen for configuring pluggable transports.

Tor Network Settings “Does your Internet Service Provider (ISP) block or otherwise censor connections to the Tor Network?” screen with “Yes” selected.

On the pluggable transport screen, select Connect with provided bridges and choose either meek-amazon or meek-google from the list. Probably both of them will work for you, so choose whichever feels faster. If one of them doesn’t work, try the other. Then click the Connect button.

Tor Network Settings “You may use the provided set of bridges or you may obtain and enter a custom set of bridges.” screen with “meek-google” selected.

If it doesn’t work, you can write to the tor-dev mailing list, or to me personally at dcf@torproject.org, or file a new ticket.

Aug 13, 2014

Welcome to the thirty-second issue of Tor Weekly News in 2014, the weekly newsletter that covers what is happening in the Tor community.

Torsocks 2.0 is now considered stable

Torsocks is a wrapper program that will force an application’s network connections to go through the Tor network. David Goulet released version 2.0.0, blessing the new codebase as stable after more than a year of efforts.

David’s original email highlighted several reasons for a complete rewrite of torsocks. Among the issues were maintainability, error handling, thread safety, and a lack of proper compatibility layer for multiple architectures. The new implementation addresses all these issues while staying about the same size as the previous version (4,000 lines of C according to sloccount), and test coverage has been vastly extended.

Torsocks comes in handy when a piece of software does not natively support the use of a SOCKS proxy. In most cases, the new version may be safer, as torsocks will prevent DNS requests and non-torified connections from happening.

Integrators and power users should watch their steps while migrating to the new version. The configuration file format has changed, and some applications might behave differently as more system calls are now restricted.

Next generation Hidden Services and Introduction Points

When Tor clients need to connect to a Hidden Service, the first step is to create a circuit to its “Introduction Point”. There, the Tor client serving the Hidden Service will be waiting through another circuit to agree on a “Rendezvous Point” and pursue the communication through circuits connecting to this freshly selected Tor node.

This general design is not subject to any changes in the revision of hidden services currently being worked on. But there are still some questions left unanswered regarding the best way to select Introduction Points. George Kadianakis summarized them as: “How many IPs should an HS have? Which relays can be IPs? What’s the lifetime of an IP?”

For each of these questions, George collected possible answers and assessed whether or not they could respond to several attacks identified in the past. Anyone interested should help with the research needed and join the discussion.

In the meantime, Michael Rogers is also trying to find ways to improve hidden service performance in mobile contexts. One way to do so would be to “keep the set of introduction points as stable as possible”. However, a naive approach to doing so would ease the job of attackers trying to locate a hidden service. The idea would be to always use the same guard and middle node for a given introduction point, but this might also open the doors to new attacks. Michael suggests experimenting with the recently published Java research framework to gain a better understanding of the implications.

More status reports for July 2014

The wave of regular monthly reports from Tor project members for the month of July continued, with submissions from Andrew Lewman, Colin C., and Damian Johnson.

Roger Dingledine sent out the report for SponsorF. Arturo Filastò described what the OONI team was up to. The Tails team covered their activity for June and July.

Miscellaneous news

Two Tor Browser releases are at QA stage: 4.0-alpha-1 including meek and a new directory layout, and 3.6.4 for security fixes.

The recent serious attack against Tor hidden services was also a Sybil attack: a large number of malicious nodes joined the network at once. This led to a renewal of interest in detecting Sybil attacks against the Tor network more quickly. Karsten Loesing published some code computing similarity metrics, and David Fifield has explored visualizations of the consensus that made the recent attack visible.

Gareth Owen sent out an update about the Java Tor Research Framework. This prompted a discussion with George Kadianakis and Tim about the best way to perform fuzz testing on Tor. Have a look if you want to comment on Tim’s approaches.

Thanks to Daniel Thill for running a mirror of the Tor Project website!

ban mentioned a new service collecting donations for the Tor network. OnionTip, set up by Donncha O’Cearbhaill, will collect bitcoins and redistribute them to relay operators who put a bitcoin address in their contact information. As the redistribution is currently done according to the consensus weight, Sebastian Hahn warned that this might encourage people to “cheat the consensus weight” because that now means “more money from oniontip”.

Juha Nurmi sent another update on the ahmia.fi GSoC project.

News from Tor StackExchange

arvee wants to redirect some TCP connections through Tor on OS X; Redsocks should help to route packets for port 443 over Tor . mirimir explained that given the user's pf configuration, the setting “SocksPort 8888” was probably missing.

meee asked a question and offered a bounty for an answer: the circuit handshake entry in Tor’s log file contains some numbers, and meee wants to know what their meaning is: “Circuit handshake stats since last time: 1833867/1833868 TAP, 159257/159257 NTor.”

Easy development tasks to get involved with

The bridge distributor BridgeDB usually gives out bridges by responding to user requests via HTTPS and email. A while ago, BridgeDB also gave out bridges to a very small number of people who would then redistribute bridges using their social network. We would like to resume sending bridges to these people, but only if BridgeDB can be made to send them via GnuPG-encrypted emails. If you’d like to dive into the BridgeDB code and add support for GnuPG-encrypted emails, please take a look at the ticket and give it a try.


This issue of Tor Weekly News has been assembled by Lunar, qbi, Karsten Loesing, harmony, and Philipp Winter.

Want to continue reading TWN? Please help us create this newsletter. We still need more volunteers to watch the Tor community and report important news. Please see the project page, write down your name and subscribe to the team mailing list if you want to get involved!

Aug 12, 2014

The fourth pointfix release of the 3.6 series is available from the Tor Browser Project page and also from our distribution directory.

This release features an update to OpenSSL to address the latest round of OpenSSL security issues. Tor Browser should only be vulnerable to one of these issues - the null pointer dereference. As this issue is only a DoS, we are not considering this a critical security update, but users are advised to upgrade anyway. This release also features an update to Tor to alert users of the RELAY_EARLY attack via a log message, and a fix for a hang that was happening to some users at startup/Tor network bootstrap.

Here is the complete changelog for 3.6.4:

  • Tor Browser 3.6.4 -- All Platforms
    • Update Tor to 0.2.4.23
    • Update Tor launcher to 0.2.5.6
    • Update OpenSSL to 1.0.1i
    • Backported Tor Patches:
      • Bug 11654: Properly apply the fix for malformed bug11156 log message
      • Bug 11200: Fix a hang during bootstrap introduced in the initial
        bug11200 patch.
    • Update NoScript to 2.6.8.36
      • Bug 9516: Send Tor Launcher log messages to Browser Console
    • Update Torbutton to 1.6.11.1
      • Bug 11472: Adjust about:tor font and logo positioning to avoid overlap
      • Bug 12680: Fix Torbutton about url.

In addition, we are also releasing the first alpha of the 4.0 series, available for download on the extended downloads page.

This alpha paves the way to our upcoming autoupdater by reorganizing the directory structure of the browser. This means that in-place upgrades from Tor Browser 3.6 (by extracting/copying over the old directory) will not work.

This release also features Tor 0.2.5.6, and some new defaults for NoScript to make the script permissions for a given url bar domain automatically cascade to all third parties by default (though this may be changed in the NoScript configuration).

  • Tor Browser 4.0-alpha-1 -- All Platforms
    • Ticket 10935: Include the Meek Pluggable Transport (version 0.10)
      • Two modes of Meek are provided: Meek over Google and Meek over Amazon
    • Update Firefox to 24.7.0esr
    • Update Tor to 0.2.5.6-alpha
    • Update OpenSSL to 1.0.1i
    • Update NoScript to 2.6.8.36
      • Script permissions now apply based on URL bar
    • Update HTTPS Everywhere to 5.0development.0
    • Update Torbutton to 1.6.12.0
      • Bug 12221: Remove obsolete Javascript components from the toggle era
      • Bug 10819: Bind new third party isolation pref to Torbutton security UI
      • Bug 9268: Fix some window resizing corner cases with DPI and taskbar size.
      • Bug 12680: Change Torbutton URL in about dialog.
      • Bug 11472: Adjust about:tor font and logo positioning to avoid overlap
      • Bug 9531: Workaround to avoid rare hangs during New Identity
    • Update Tor Launcher to 0.2.6.2
      • Bug 11199: Improve behavior if tor exits
      • Bug 12451: Add option to hide TBB's logo
      • Bug 11193: Change "Tor Browser Bundle" to "Tor Browser"
      • Bug 11471: Ensure text fits the initial configuration dialog
      • Bug 9516: Send Tor Launcher log messages to Browser Console
    • Bug 11641: Reorganize bundle directory structure to mimic Firefox
    • Bug 10819: Create a preference to enable/disable third party isolation
    • Backported Tor Patches:
      • Bug 11200: Fix a hang during bootstrap introduced in the initial
        bug11200 patch.
  • Tor Browser 4.0-alpha-1 -- Linux Changes
    • Bug 10178: Make it easier to set an alternate Tor control port and password
    • Bug 11102: Set Window Class to "Tor Browser" to aid in Desktop navigation
    • Bug 12249: Don't create PT debug files anymore

The list of frequently encountered known issues is also available in our bug tracker.

Aug 06, 2014

Welcome to the thirty-first issue of Tor Weekly News in 2014, the weekly newsletter that covers what is happening in the Tor community.

Tor and the RELAY_EARLY traffic confirmation attack

Roger Dingledine ended several months of concern and speculation in the Tor community with a security advisory posted to the tor-announce mailing list and the Tor blog.

In it, he gave details of a five-month-long active attack on operators and users of Tor hidden services that involved a variant of the so-called “Sybil attack”: the attacker signed up “around 115 fast non-exit relays” (now removed from the Tor network), and configured them to inject a traffic header signal consisting of RELAY_EARLY cells to “tag” any hidden service descriptor requests received by malicious relays — a tag which could then be picked up by other bad nodes acting as entry guards, in the process identifying clients which requested information about a particular hidden service.

The attack is suspected to be linked to a now-cancelled talk that was due to be delivered at the BlackHat security conference. There have been several fruitful and positive research projects involving theoretical attacks on Tor’s security, but this was not among them. Not only were there problems with the process of responsible disclosure, but, as Roger wrote, “the attacker encoded the name of the hidden service in the injected signal (as opposed to, say, sending a random number and keeping a local list mapping random number to hidden service name)”, thereby “[putting] users at risk indefinitely into the future”.

On the other hand, it is important to note that “while this particular variant of the traffic confirmation attack allows high-confidence and efficient correlation, the general class of passive (statistical) traffic confirmation attacks remains unsolved and would likely have worked just fine here”. In other words, the tagging mechanism used in this case is the innovation; the other element of the attack is a known weakness of low-latency anonymity systems, and defending against it is a much harder problem.

“Users who operated or accessed hidden services from early February through July 4 should assume they were affected” and act accordingly; in the case of hidden service operators, this may mean changing the location of the service. Accompanying the advisory were two new releases for both the stable and alpha tor branches (0.2.4.23 and 0.2.5.6-alpha); both include a fix for the signal-injection issue that causes tor to drop circuits and give a warning if RELAY_EARLY cells are detected going in the wrong direction (towards the client), and both prepare the ground for clients to move to single entry guards (rather than sets of three) in the near future. Relay operators should be sure to upgrade; a point-release of the Tor Browser will offer the same fixes to ordinary users. Nusenu suggested that relay operators regularly check their logs for the new warning, “even if the attack origin is not directly attributable from a relay’s point of view”. Be sure to read the full security advisory for a fuller explanation of the attack and its implications.

Why is bad-relays a closed mailing list?

Damian Johnson and Philipp Winter have been working on improving the process of reporting bad relays. The process starts by having users report odd behaviors to the bad-relays mailing list.

Only a few trusted volunteers receive and review these reports. Nusenu started a discussion on tor-talk advocating for more transparency. Nusenu argues that an open list would “likely get more confirm/can’t confirm feedback for a given badexit candidate”, and that it would allow worried users to act faster than operators of directory authorities.

Despite being “usually on the side of transparency”, Roger Dingledine described being “stuck” on the issue, “because the arms race is so lopsidedly against us”.

Roger explains: “we can scan for whether exit relays handle certain websites poorly, but if the list that we scan for is public, then exit relays can mess with other websites and know they’ll get away with it. We can scan for incorrect behavior on various ports, but if the list of ports and the set of behavior we do is public, then again relays are free to mess with things we don’t look for.”

A better future and more transparency probably lies in adaptive test systems run by multiple volunteer groups. Until they come to existence, as a small improvement, Philipp Winter wrote it was probably safe to publish why relays were disabled, through “short sentence along the lines of ‘running HTTPS MitM’ or ‘running sslstrip’”.

Monthly status reports for July 2014

Time for monthly reports from Tor project members. The July 2014 round was opened by Georg Koppen, followed by Philipp Winter, Sherief Alaa, Lunar, Nick Mathewson, Pearl Crescent, George Kadianakis, Matt Pagan, Isis Lovecruft, Griffin Boyce, Arthur Edelstein, and Karsten Loesing.

Lunar reported on behalf of the help desk and Mike Perry for the Tor Browser team.

Miscellaneous news

Anthony G. Basile announced a new release of tor-ramdisk, an i686 or x86_64 uClibc-based micro Linux distribution whose only purpose is to host a Tor server. Version 20140801 updates Tor to version 0.2.4.23, and the kernel to 3.15.7 with Gentoo’s hardened patches.

meejah has announced a new command-line application. carml is a versatile set of tools to “query and control a running Tor”. It can do things like “list and remove streams and circuits; monitor stream, circuit and address-map events; watch for any Tor event and print it (or many) out; monitor bandwidth; run any Tor control-protocol command; pipe through common Unix tools like grep, less, cut, etcetera; download TBB through Tor, with pinned certs and signature checking; and even spit out and run xplanet configs (with router/circuit markers)!” The application is written in Python and uses the txtorcon library. meejah describes it as early-alpha and warns that it might contain “serious, anonymity-destroying bugs”. Watch out!

Only two weeks left for the Google Summer of Code students, and the last round of reports but one: Juha Nurmi on the ahmia.fi project, Marc Juarez on website fingerprinting defenses, Amogh Pradeep on Orbot and Orfox improvements, Zack Mullaly on the HTTPS Everywhere secure ruleset update mechanism, Israel Leiva on the GetTor revamp, Quinn Jarrell on the pluggable transport combiner, Daniel Martí on incremental updates to consensus documents, Noah Rahman on Stegotorus enhancements, and Sreenatha Bhatlapenumarthi on the Tor Weather rewrite.

The Tails team is looking for testers to solve a possible incompatibility in one of the recommended installation procedures. If you have a running Tails system, a spare USB stick and some time, please help. Don’t miss the recommended command-line options!

The Citizen Lab Summer Institute took place at the University of Toronto from July 28 to 31. The event brought together policy and technology researchers who focus on Internet censorship and measurement. A lot of great work was presented including but not limited to a proposal to measure the chilling effect, ongoing work to deploy Telex, and several projects to measure censorship in different countries. Some Tor-related work was also presented: Researchers are working on understanding how the Tor network is used for political purposes. Another project makes use of TCP/IP side channels to measure the reachability of Tor relays from within China.

The Electronic Frontier Foundation wrote two blog posts to show why Tor is important for universities and how universities can help the Tor network. The first part explains why Tor matters, gives several examples of universities already contributing to the Tor network, and outlines a few reasons for hosting new Tor nodes. The second part gives actual tips on where to start, and how to do it best.

Tor help desk roundup

Users occasionally ask if there is any way to set Tor Browser as the default browser on their system. Currently this is not possible, although it may be possible in a future Tor Browser release. In the mean time, Tails provides another way to prevent accidentally opening hyperlinks in a non-Tor browser.

Easy development tasks to get involved with

Tor Launcher is the Tor controller shipped with Tor Browser written in JavaScript. Starting with Firefox 14 the “nsILocalFile” interface has been deprecated and replaced with the “nsIFile” interface. What we should do is replace all instances of “nsILocalFile” with “nsIFile” and see if anything else needs fixing to make Tor Launcher still work as expected. If you know a little bit about Firefox extensions and want to give this a try, clone the repository, make the necessary changes, run “make package”, and tell us whether something broke in interesting ways.


This issue of Tor Weekly News has been assembled by Lunar, harmony, Matt Pagan, Philipp Winter, David Fifield, Karsten Loesing, and Roger Dingledine.

Want to continue reading TWN? Please help us create this newsletter. We still need more volunteers to watch the Tor community and report important news. Please see the project page, write down your name and subscribe to the team mailing list if you want to get involved!