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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

Oct 23, 2014

We are happy to announce the fourth beta release of TorBirdy: 0.1.3. All users are encouraged to upgrade as soon as possible, especially if you are using Thunderbird 31.

Notable changes in this release include:

0.1.3, 23 Oct 2014

* The default keyserver (hidden service) has been updated:
- hkp://qdigse2yzvuglcix.onion
* Show the Sender header in message pane (closes #10226)
* Draft messages on IMAP accounts are now saved locally (closes #10309)
* Restore preferences to the user's own defaults instead of Thunderbird's
(closes #10588)
* network.proxy.no_proxies_on is no longer set to "localhost, 127.0.0.1"
(thanks to Carsten N.)
* Disable automatic downloading of new messages for POP3 accounts
(closes #11188)
* Update the reply_header author behaviour (closes #13480)
* TorBirdy is now available in 31 languages:
- Arabic
- Catalan
- Czech
- Danish
- German
- Greek
- English (US)
- English (Great Britain)
- Spanish
- Basque
- French
- Hebrew
- Hungarian
- Indonesian
- Italian
- Korean
- Latvian
- Norwegian Bokmål
- Norwegian Nynorsk
- Punjabi
- Polish
- Portuguese
- Portuguese (Brazil)
- Romanian
- Russian
- Slovak
- Slovenian
- Serbian
- Swedish
- Turkish
- Ukrainian

We offer two ways of installing TorBirdy -- either by visiting our website (sig) or by visiting the Mozilla Add-ons page for TorBirdy. Please note that there may be a delay -- which can range from a few hours to days -- before the extension is reviewed by Mozilla and updated on the Add-ons page.

As a general anonymity and security note: we are still working on two known anonymity issues with Mozilla. Please make sure that you read the Before Using TorBirdy and Known TorBirdy Issues sections on the wiki before using TorBirdy.

We had love help with getting our patches accepted, or anything that you think will help improve TorBirdy!

Feel free to follow along with the release on the tor-talk mailing list.

Oct 22, 2014

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

Tor 0.2.5.9-rc is out

Nick Mathewson announced what is hopefully the final release candidate in the Tor 0.2.5 series. It contains two enhancements in response to the recent POODLE attack on OpenSSL, “even though POODLE does not affect Tor”, as well as a number of other miscellaneous improvements.

Upgrading is especially important for relay operators, as a remote crash is possible when older Tor versions are used with a version of OpenSSL released last week that was built with the “no-ssl3” flag.

As ever, you can download the source code from the distribution directory and packages should follow shortly.

Tor Browser 4.0 is out

Mike Perry announced a major release by the Tor Browser team. Version 4.0 of the secure and anonymous web browser brings several exciting new features to the stable series, including the meek censorship-circumvention tool, the secure updater, and a simplified Javascript enabling/disabling process in NoScript, all based on a customized Firefox ESR31. SSLv3 is also disabled, in response to the recent POODLE attack.

This release contains important security fixes, and all users should upgrade as soon as possible. Please note that the new directory structure means users cannot simply extract the new Tor Browser over their existing 3.6.6 directory, and must instead delete the old version entirely. The secure updater still requires manual activation in the “About Tor Browser” menu option, as its security will depend “on the specific CA that issued the www.torproject.org HTTPS certificate (Digicert)” until site-specific certificate pinning and signed update files are implemented. Furthermore, “we still need to improve meek’s performance to match other transports”, wrote Mike, “so adjust your expectations accordingly”.

See Mike’s post for further details and a full changelog, and get your copy of Tor Browser 4.0 from the distribution directory or the download page.

Tails 1.2 is out

The Tails team put out version 1.2 of the anonymizing live operating system. This release replaces the Iceweasel browser with “most of” the regular Tor Browser, and confines several important applications with AppArmor.

I2P will now, like Tor, be started upon network connection if activated with the “i2p” boot parameter, and must be used with the new dedicated I2P Browser. This is also the last Tails release to ship with the now-unmaintained TrueCrypt tool, but the Tails team has already documented the method for opening TrueCrypt volumes with cryptsetup. See the team’s announcement for a full list of changes in the new version.

This is an important security release and all users should upgrade as soon as possible. If you have a running Tails, you should be able to use the incremental updater; if your Tails drive was manually created, or you are a new user, head to the download page for more information.

Miscellaneous news

tagnaq warned users of TorBirdy, the torifying extension for the Thunderbird mail client, that a change in Thunderbird 31’s handling of the “reply_header_authorwrote” header means that the word “wrote”, translated into the user’s system language, may be inserted before quoted text when replying to emails, leaking the system language to recipients of replies if not removed. Jacob Appelbaum responded that a new release of TorBirdy addressing this and other issues was imminent.

Arturo Filastò announced the release of ooniprobe 1.1.2, containing “two new report entry keys, test_start_time and test_runtime”, and a fix for a bug that “led to ooniresources not working properly”.

evilaliv3 announced version 3.1.20 of tor2web, an HTTP proxy that enables access to hidden services without a Tor client, for users who do not require strong anonymity. As well as “some networking bugfixing and optimizations”, this release adds a “replace” mode for remotely-fetched blocklists in addition to “merge”, and a feature that allows different hostnames to be mapped to specific hidden services.

Karsten Loesing gave users of Onionoo a “one-month heads-up” that on or after November 15th, a change to the protocol will let the search parameter “accept base64-encoded fingerprints in addition to hex-encoded fingerprints, nicknames, and IP addresses.” These searches will also return relays whose base64-encoded fingerprints are a partial match for the search string. “If you’re fine with that, feel free to ignore this message and do nothing”, but if not, “you’ll have to filter out those relays locally”.

Following updates to the Tor Project’s website, Sebastian Hahn drew attention to a change in the steps necessary to run a website mirror. “Please ask if you run into any trouble, and thanks for providing a mirror!”

Inspired by “the Directory Authorities, the crappy experiment leading up to Black Hat, and the promise that one can recreate the Tor network in the event of some catastrophe”, Tom Ritter sent out a detailed report of issues he encountered while setting up his own Tor network using “full-featured independent tor daemons”, rather than a network simulator like Shadow or Chutney.

Cthulhu asked for assistance in overhauling the GoodBadISP page, which is the starting point for many relay operators around the world. If you have some time to spare, or know some ISPs not yet on the list, it would be greatly appreciated if they could be added to the page. This new effort to reach out to hosting providers could be of great value after years of what Roger Dingledine has described as a “slash and burn” agriculture model of operating Tor nodes.

Vladimir Martyanov started a discussion on the question of whether Tor developers should ensure that tor can still be built using compilers that do not support the C99 programming language standard, such as older versions of Microsoft Visual Studio.


This issue of Tor Weekly News has been assembled by Lunar, Cthulhu, Roger Dingledine, Karsten Loesing, and Harmony.

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!

Oct 21, 2014

Tor misused by criminals

Several people contacted The Tor Project recently because some software told them to install the Tor Browser to access a website. There is no affiliation between these criminals and Tor.

What happened here?

The computer is probably infected with what's called ransomware. This is a kind of malicious software which restricts access to the files and demands a ransom. In this case the authors of the ransomware CryptoLocker set up a website which is only reachable by using Tor. That is why people are thinking that the software is somehow related to The Tor Project.

In fact, CryptoLocker is unrelated to The Tor Project. We didn't produce it, and we didn't ask to be included in the criminal infection of any computer. We cannot help you with your infection. However, according to the BBC you may be able to decrypt your files for free. If not, Bleeping Computer can provide more information.

We, the people of Tor, are very sorry to hear, that some individual misused the anonymity granted by our service. The vast majority of our users use Tor in a responsible way. Thank you for your understanding.

Oct 21, 2014

This is a copy of the message Nick Mathewson sent to the tor-talk & tor-relays mailing lists.

Hello, relay operators!

There's one important bugfix in the 0.2.5.9-rc release that relay operators should know about. If you have a version of OpenSSL that came out last week (like 1.0.1j, 1.0.0, ) and if your version of OpenSSL is built with the "no-ssl3" flag, then it's possible to crash your Tor relay remotely if you don't upgrade to 0.2.5.9-rc or to 0.2.4.25 (when that's out).

This appears to be an OpenSSL bug. The Tor releases in question contain a workaround for it.

To tell if your version of OpenSSL was built with 'no-ssl3': run:

openssl s_client -ssl3 -connect www.torproject.org:443

If it gives you output beginning with something like:

CONNECTED(00000003)
140632971298688:error:14094410:SSL routines:SSL3_READ_BYTES:sslv3
alert handshake failure:s3_pkt.c:1257:SSL alert number 40
140632971298688:error:1409E0E5:SSL routines:SSL3_WRITE_BYTES:ssl
handshake failure:s3_pkt.c:596:

then you're fine and you don't need to upgrade Tor on your relay. But if it says something that starts with:

unknown option -ssl3
usage: s_client args

then you need to upgrade Tor.

Some questions and answers:

Q: Does this affect clients?
A: No. Only relays.

Q: Does this affect me if I'm running a version of OpenSSL other than 1.0.1j, 1.0.0o, or 0.9.8zc?
A: No. Only those versions.

Q: Does this affect me if I'm running a version of OpenSSL configured without the "no-ssl3" option?
A: No. Only versions that were built with the "no-ssl3" option are affected.

Q: Does the OpenSSL team know?
A: Yes. Have a look at this thread. Also, before I saw that thread, I informed them the other day.

Q: Does this affect Tor packages?
A: I don't think that we shipped any packages where we used the "no-ssl3" flag to diable ssl3. So only if you're using OpenSSL from another source (say, your operating system) will you be affected.

Q: What can I do to remediate this problem?
A: You can upgrade to the most recent Tor, or you can use a version of OpenSSL built without the "no-ssl3" flag. Downgrading your OpenSSL is not recommended.

Q: What is the potential impact of this bug?
A: If a relay is affected by this bug, anybody can make the relay crash remotely. It does not enable any data leaks or remote code execution. Still, the ability to selectively disable relays might enable a sophisticated attacker to do some kinds of traffic analysis more efficiently. So, fix your relay if it's affected.

Q: Should we run in circles and freak out?
A: Not this time. We should just make sure we fix affected relays.

Q: Hey, Nick, you didn't explain this properly!
A: Please send a follow-up message that explains it better. :)

Oct 16, 2014

Tails, The Amnesic Incognito Live System, version 1.2, is out.

This release fixes numerous security issues and all users must upgrade as soon as possible.

Changes

Notable user-visible changes include:

  • Major new features
    • Install (most of) the Tor Browser, replacing our previous Iceweasel-based browser. The version installed is from TBB 4.0 and is based on Firefox 31.2.0esr. This fixes the POODLE vulnerability.
    • Upgrade Tor to 0.2.5.8-rc.
    • Confine several important applications with AppArmor.
  • Bugfixes
    • Install Linux 3.16-3 (version 3.16.5-1).
  • Minor improvements
    • Upgrade I2P to 0.9.15, and isolate I2P traffic from the Tor Browser by adding a dedicated I2P Browser. Also, start I2P automatically upon network connection, when the i2p boot option is added.
    • Make it clear that TrueCrypt will be removed in Tails 1.2.1 (ticket #7739), and document how to open TrueCrypt volumes with cryptsetup.
    • Enable VirtualBox guest additions by default (ticket #5730). In particular this enables VirtualBox's display management service.
    • Make the OTR status in Pidgin clearer thanks to the formatting toolbar (ticket #7356).
    • Upgrade syslinux to 6.03-pre20, which should fix UEFI boot on some hardware.

See the online Changelog for technical details.

Known issues

I want to try it or to upgrade!

Go to the download page.

As no software is ever perfect, we maintain a list of problems that affects the last release of Tails.

What's coming up?

The next Tails release is scheduled for November 25.

Have a look to our roadmap to see where we are heading to.

Do you want to help? There are many ways you can contribute to Tails. If you want to help, come talk
to us!

Support and feedback

For support and feedback, visit the Support section on the Tails website.

Oct 15, 2014

Update (Oct 22 13:15 UTC): Windows users that are affected by Tor Browser crashes might try to avoid this problem by opening "about:config" and setting the preference "media.directshow.enabled" to "false". This is a workaround reported to help while the investigation is still on-going.

Update (Oct 25 02:32 UTC): If you are unhappy with the new Firefox 31 UI, please check out Classic Theme Restorer.

Update (Oct 16 20:35 UTC): The meek transport still needs performance tuning before it matches other more conventional transports. Ticket numbers are now listed in the post.

The first release of the 4.0 series is available from the Tor Browser Project page and also from our distribution directory.

This release features important security updates to Firefox. Additionally, due to the POODLE attack, we have also disabled SSLv3 in this release.

The primary user-facing change since the 3.6 series is the transition to Firefox 31-ESR.

More importantly for censored users who were using 3.6, the 4.0 series also features the addition of three versions of the meek pluggable transport. In fact, we believe that both meek-amazon and meek-azure will work in China today, without the need to obtain bridge addresses. Note though that we still need to improve meek's performance to match other transports, though. so adjust your expectations accordingly. See tickets #12428, #12778, and #12857 for details.

This release also features an in-browser updater, and a completely reorganized bundle directory structure to make this updater possible. This means that simply extracting a 4.0 Tor Browser over a 3.6.6 Tor Browser will not work. Please also be aware that the security of the updater depends on the specific CA that issued the www.torproject.org HTTPS certificate (Digicert), and so it still must be activated manually through the Help ("?") "about browser" menu option. Very soon, we will support both strong HTTPS site-specific certificate pinning (ticket #11955) and update package signatures (ticket #13379). Until then, we do not recommend using this updater if you need stronger security and normally verify GPG signatures.

There are also a couple behavioral changes relating to NoScript since 3.6. In particular, by default it now enforces script enable/disable for all sub-elements of a page, so you only need to enable scripts once for a page to work, rather than enabling many sub-scripts. This will hopefully make it possible for more people to use the "High Security" setting in our upcoming Security Slider, which will have Javascript disabled globally via NoScript by default. While we do not recommend per-element whitelisting due to fingerprinting, users who insist on keeping this functionality may wish to check out RequestPolicy.

Note to MacOS users: We intend to deprecate 32bit OSX bundles very soon. If you are still using 32bit OSX 10.6, you soon will need to either update your OS to a later version, or begin using the Tails live operating system.

Here is the changelog since 4.0-alpha-3:

  • All Platforms
    • Update Firefox to 31.2.0esr
    • Update Torbutton to 1.7.0.1
      • Bug 13378: Prevent addon reordering in toolbars on first-run.
      • Bug 10751: Adapt Torbutton to ESR31's Australis UI.
      • Bug 13138: ESR31-about:tor shows "Tor is not working"
      • Bug 12947: Adapt session storage blocker to ESR 31.
      • Bug 10716: Take care of drag/drop events in ESR 31.
      • Bug 13366: Fix cert exemption dialog when disk storage is enabled.
    • Update Tor Launcher to 0.2.7.0.1
      • Translation updates only
    • Udate fteproxy to 0.2.19
    • Update NoScript to 2.6.9.1
    • Bug 13027: Spoof window.navigator useragent values in JS WebWorker threads
    • Bug 13016: Hide CSS -moz-osx-font-smoothing values.
    • Bug 13356: Meek and other symlinks missing after complete update.
    • Bug 13025: Spoof screen orientation to landscape-primary.
    • Bug 13346: Disable Firefox "slow to start" warnings and recordkeeping.
    • Bug 13318: Minimize number of buttons on the browser toolbar.
    • Bug 10715: Enable WebGL on Windows (still click-to-play via NoScript)
    • Bug 13023: Disable the gamepad API.
    • Bug 13021: Prompt before allowing Canvas isPointIn*() calls.
    • Bug 12460: Several cross-compilation and gitian fixes (see child tickets)
    • Bug 13186: Disable DOM Performance timers
    • Bug 13028: Defense-in-depth checks for OCSP/Cert validation proxy usage
    • Bug 13416: Defend against new SSLv3 attack (poodle).


Here is the list of all changes in the 4.0 series since 3.6.6:

  • All Platforms
    • Update Firefox to 31.2.0esr
    • Udate fteproxy to 0.2.19
    • Update Tor to 0.2.5.8-rc (from 0.2.4.24)
    • Update NoScript to 2.6.9.1
    • Update Torbutton to 1.7.0.1 (from 1.6.12.3)
      • Bug 13378: Prevent addon reordering in toolbars on first-run.
      • Bug 10751: Adapt Torbutton to ESR31's Australis UI.
      • Bug 13138: ESR31-about:tor shows "Tor is not working"
      • Bug 12947: Adapt session storage blocker to ESR 31.
      • Bug 10716: Take care of drag/drop events in ESR 31.
      • Bug 13366: Fix cert exemption dialog when disk storage is enabled.
    • Update Tor Launcher to 0.2.7.0.1 (from 0.2.5.6)
      • Bug 11405: Remove firewall prompt from wizard.
      • Bug 12895: Mention @riseup.net as a valid bridge request email address
      • Bug 12444: Provide feedback when “Copy Tor Log” is clicked.
      • Bug 11199: Improve error messages if Tor exits unexpectedly
      • 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 13027: Spoof window.navigator useragent values in JS WebWorker threads
    • Bug 13016: Hide CSS -moz-osx-font-smoothing values.
    • Bug 13356: Meek and other symlinks missing after complete update.
    • Bug 13025: Spoof screen orientation to landscape-primary.
    • Bug 13346: Disable Firefox "slow to start" warnings and recordkeeping.
    • Bug 13318: Minimize number of buttons on the browser toolbar.
    • Bug 10715: Enable WebGL on Windows (still click-to-play via NoScript)
    • Bug 13023: Disable the gamepad API.
    • Bug 13021: Prompt before allowing Canvas isPointIn*() calls.
    • Bug 12460: Several cross-compilation and gitian fixes (see child tickets)
    • Bug 13186: Disable DOM Performance timers
    • Bug 13028: Defense-in-depth checks for OCSP/Cert validation proxy usage
    • Bug 4234: Automatic Update support (off by default)
    • Bug 11641: Reorganize bundle directory structure to mimic Firefox
    • Bug 10819: Create a preference to enable/disable third party isolation
    • Bug 13416: Defend against new SSLv3 attack (poodle).
  • Windows:
    • Bug 10065: Enable DEP, ASLR, and SSP hardening options
  • Linux:
    • Bug 13031: Add full RELRO hardening protection.
    • 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.

Oct 15, 2014

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

Academic research into Tor: four recent studies

Major contributions to the development and security of Tor are often made by academic researchers, either in a laboratory setting using network simulators like Shadow, or through measurement and analysis of the live network itself (taking care not to harm the security or anonymity of clients and services). Different aspects of Tor’s networking and security, from path selection to theoretical attacks, have been analysed in three recently-published studies.

Otto Huhta’s MSc thesis investigates the possibility that an adversary in control of a non-exit relay could link two or more Tor circuits back to the same client based on nothing more than timing information. As Otto explained, “this is mainly the result of the fixed 10 minute circuit lifetime and the fact that the transition to using a new circuit is quite sharp.” With the help of a machine classifier, and the fact that any one client will build its circuits through a fixed set of entry guards, the study suggested that such an adversary “can focus only on circuits built through these specific nodes and quite efficiently determine if two circuits belong to the same user.” There is no suggestion that this knowledge alone poses a serious deanonymization risk to clients; however, wrote Otto, “our goal was not to ultimately break the anonymity of any real user but instead to expose a previously unknown threat so that it can be mitigated before anyone actually devises an attack around it.”

Steven Murdoch published a paper on the optimization of Tor’s node selection probabilities showing, in Steven’s words, “that what Tor used to do (distributing traffic to nodes in proportion to their contribution to network capacity) is not the best approach.” Prior to publication of the study, “Tor moved to actively measuring the network performance and manipulating the consensus weights in response to changes. This seems to have ended up with roughly the same outcome. […] However, the disadvantage is that it can only react slowly to changes in network characteristics.”

Sebastian Urbach shared a link to “Defending Tor from Network Adversaries: A Case Study of Network Path Prediction”, in which the researchers analyze the effect of network features like autonomous systems and Internet exchanges on the security of Tor’s path selection, finding that “AS and IX path prediction significantly overestimates the threat of vulnerability to such adversaries”, and that “the use of active path measurement, rather than AS path models” would be preferable “in further study of Tor vulnerability to AS- and IX-level adversaries and development of practical defenses.”

Meanwhile, Philipp Winter took to the Tor blog to summarize some new findings concerning the the way in which the Chinese state Internet censorship system (the “Great Firewall of China”) acts upon blocked connections, like those trying to reach Tor, as detailed in a recent project to which he contributed. Searching for spatial and temporal patterns in Chinese censorship activity, the researchers found that “many IP addresses inside the China Education and Research Network (CERNET) are able to connect” to Tor in certain instances, while the filtering of other networks — centrally conducted at the level of Internet exchanges — “seems to be quite effective despite occasional country-wide downtimes”.

Each of these studies is up for discussion on the tor-dev mailing list, so feel free to join in there with questions and comments for the researchers!

Miscellaneous news

Michael Rogers submitted patches against tor and jtorctl, making two improvements to the performance of mobile hidden services: one “avoids a problem where we’d try to build introduction circuits immediately, all the circuits would fail, and we’d wait for 5 minutes before trying again”, and the other “[adds] a command to the control protocol to purge any cached state relating to a specified hidden service”.

Karsten Loesing published a “non-functional” mock-up of a possible redesign for the Tor Metrics portal, with notes on design decisions: “Feedback much appreciated. This is the perfect time to consider your ideas.”

Jeremy Gillula analyzed data relating to Tor node churn found in Tor consensuses for September 2014, and found that “on average, 0.003% of nodes switch from being relay nodes to exit nodes in any given 1-hour period, and 0.002% switch from being exit nodes to relay nodes”.

Noel Torres and Andrew Lewman sent their status reports for September. Roger Dingledine also sent out the report for SponsorF.

Greg Norcie wondered why the interval at which Tor switches to using a new circuit was set at ten minutes, and Nick Mathewson responded that after the original period of thirty seconds was found to be unworkable, the new number was selected in 2005 “more or less intuitively”. Paul Syverson added that the choice was “an informed one”, taken after “a bunch of discussions concerning the trade-offs between the overhead of the public-key operations of circuit building and the pseudonymous profiling occurring at an exit”.

Both Tor and Tails received their first cinematic credits with the première of “CITIZENFOUR”, a documentary film concerning the recent disclosure of intelligence documents by Edward Snowden. Eagle-eyed viewers might spot a well-known hostname in the film’s trailer

WhonixQubes reported on progress in many areas of the Whonix+Qubes project, which as the name implies is a combination of the Whonix and Qubes operating systems. Among other things, the system now supports Whonix 9, a community forum has been set up, and greater upstream integration is being discussed.

News from Tor StackExchange

"What happens when Tor always chooses the same path?" asks Mark and wants to know which weaknesses this exposes. User194 believes that this would prevent a “predecessor attack” and make the system stronger, while Lisbeth writes: “This makes your entire traffic highly fingerprintable as compared to a standard random path. If your connections always used A, B, and C nodes, it is statistically unlikely that many other people are consistently using that same path, therefore it’s very easy to correlate your traffic to your originating IP.”

Muncher visited a website which asked to add HidServAuth into the torrc and wants to know if it is safe to do so. Jeff recommended that this is safe because it doesn’t divulge anything about the identity of a user. Mirimir furthermore referred to a question where adrelanos looks for documentation.


This issue of Tor Weekly News has been assembled by Lunar, qbi, and Harmony.

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!

Oct 15, 2014

Hi! It's a new month, so that means there's a new attack on TLS.

This time, the attack is that many clients, when they find a server that doesn't support TLS, will downgrade to the ancient SSLv3. And SSLv3 is subject to a new padding oracle attack.

There is a readable summary of the issue at Adam Langley's blog; it links to other descriptions of the attack.

Tor itself is not affected: all released versions for a long time have shipped with TLSv1 enabled, and we have never had a fallback mechanism to SSLv3. Furthermore, Tor does not send the same secret encrypted in the same way in multiple connection attempts, so even if you could make Tor fall back to SSLv3, a padding oracle attack probably wouldn't help very much.

TorBrowser, on the other hand, is based on Firefox, and has the same protocol downgrade mechanisms as Firefox. I expect and hope the TorBrowser team will be
releasing a new version soon with SSLv3 disabled. But in the meantime, I think you can disable SSLv3 yourself by changing the value of the "security.tls.version.min" preference to "1". (The default value is "0".)

To do that:

  1. Enter "about:config" in the URL bar.
  2. Then you click "I'll be careful, I promise".
  3. Then enter "security.tls.version.min" in the preference "search"
    field underneath the URL bar. (Not the search box next to the URL
    bar.)

  4. You should see an entry that says "security.tls.version.min" under
    "Preference Name". Double-click on it, then enter the value "1" and
    click okay.

You should now see that the value of "security.tls.version.min" is set to one.

(Note that I am not a Firefox developer or a TorBrowser developer: if you're cautious, you might want to wait until one of them says something here before you try this workaround. On the other hand, if you believe me, you should probably do this in your regular Firefox as well.)

Obviously, this isn't a convenient way to do this; if you are uncertain of your ability to do so, waiting for an upgrade might be a good move. In the meantime, if you have serious security requirements and you cannot disable SSLv3, it might be a good idea to avoid using the Internet for a week or two while this all shakes out.

Best wishes to other residents of these interesting times.