phobos's blog

Using Tor hidden services for good

Getting good stories for Tor successes is tricky, because if Tor is doing its job, nobody notices. I know a lot of people who have really interesting Tor success stories and have no interest in telling the world who they are and how they managed (until that moment when everybody is reading about them, that is) to stay safe.

Still, there are a bunch of other stories out there that haven't been documented as well. For example, I really like Nasser's story about his experiences in Mauritania:

Hidden services have gotten less broad attention from the Tor user base, since most people who install Tor have a website in mind like twitter or indymedia that they want to visit safely. Some good use cases that we've seen for hidden services in particular include:

- I know people (for example, in countries that have been undergoing revolutions lately) who run popular blogs but their blogs kept getting knocked offline by state-sponsored jerks. The common blogging software they used (like Wordpress) couldn't stand up to the ddos attacks and breakins. The solution was to split the blog into a public side, which is static html and has no logins, and a private side for posting, which is only reachable over a Tor hidden service. Now their blog works again and they're reaching their audiences. And as a bonus, the nice fellow hosting the private side for them doesn't need to let people know where it is, and even if somebody figures it out, the nice fellow hosting it doesn't have any IP addresses to hand over or lose.

- Whistleblowing websites want to provide documents from a platform that is hard for upset corporations or governments to censor. See e.g.

- Google for 'indymedia fbi seize'. When Indymedia offers a hidden service version of their website, censoring organizations don't know which data centers to bully into handing over the hardware.

- Data retention laws in Europe (and soon in the US too at this rate) threaten to make centralized chat networks vulnerable to social network analysis (step one, collect all the data; step two, get broken into by corporations, criminals, external governments, you name it; step three comes identity theft, stalking, targeted scam jobs, etc etc). What if you had a chat network where all the users were on hidden services by default? Now there's no easy central point to learn who's talking to who and when. Building one and making it usable turns out to be hard. But good thing we have this versatile tool here as a building block.

That's a start. It is certainly the case that we (Tor) spend most of our time making the technology better, and not so much of our time figuring out how to market it and change the world's perception on whether being safe online is worthwhile. Please help. :)

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This blog post was adapted from an email to tor-talk by Roger. See the original email at

Thank you to our donors

2011 was an exciting year for communications security. Online communications helped to support activists in the Middle East's "Arab Spring" as they toppled Tunisia's Ben Ali and Egypt's Mubarak. Tor's entry nodes and hidden "bridge" entry points have seen increased usage from Iran and Syria, as citizens there seek to communicate securely and evade government censorship. Secretary of State Clinton has made Internet Freedom part of the U.S. State Department's agenda, while here in the United States, advertisers have developed more sophisticated ways to track browsers' online activity.

The Tor Project can help, but the censors and snoops are never very far behind. We must keep improving our software and network, researching its security against new threats, and training users to communicate safely. As a non-profit, we depend on your donations of money, relays, and advocacy to keep making progress.

In the past year, Tor released new versions to improve security and blocking resistance, including a same-day fix to a block detected in Iran. We have enhanced translations in more than a dozen languages including Farsi, Arabic, and Chinese; presented security and anonymity research; and taught security practices to groups including journalists, activists, law enforcement, and survivors of domestic violence.

Please help us keep the Internet open and private for all.

If you would like to keep up to date with Tor, please visit our donor thank you page at

Donate securely online at

Temporary Website Outages....are fixed

Update 2011-12-21 20:06 (GMT-5): everything is back online and operating within acceptable parameters.

As of late last night 20 Dec (GMT-5) our website hosting provider is
experiencing a sustained attack. The attack is not directed at Tor, but
someone else on the same network. The effect is that parts of our
website infrastructure are intermittently unreachable. This includes
the following domains in www, trac, gitweb, doxygen,
cloud, svn, and check.

The most visible outage is Every Tor Browser
Bundle user will attempt to reach this url on start up. You are
currently seeing a browser-generated timeout message as the site is

We're working to setup a new instance of on a
different machine today.

Originally posted to tor-talk,

November 2011 Progress Report

The progress report for November 2011 is released as pdf and plaintext documents. Highlights include progress on the new Tor Check, Tor Bulk Exitlist, global media hits, Tor Cloud launch, and three new proposals to improve Tor Bridge Relay functionality in difficult environments.

Tails 0.9 Released

The latest version of the anonymous operating system Tails is now available.

Notable user-visible changes include:

## Tor
- Upgrade to This fixes CVE-2011-2768 and CVE-2011-2769 which prompted for manual updates for users of Tails 0.8.1.
- Suppress Tor's warning about applications doing their own DNS lookups. Some users have reported concerns about these warnings, but it should be noted that they are completely harmless inside Tails as its system DNS resolver is Torified.

- Linux 3.0.0-6, which fixed a great number of bugs and security issues.

## Iceweasel
- Upgrade to 3.5.16-11 ((fixes CVE-2011-3647, CVE-2011-3648, CVE-2011-3650).
- Torbutton: upgrade to, including support for the in-browser "New identity" feature.
- FireGPG: upgrade to 0.8-1+tails2. Users are notified that the FireGPG Text Editor is the only safe place for performing cryptographic operations, and these operations has been disabled in other places. Performing them outside of the editor opens up several severe attacks through JavaScript (e.g. leaking plaintext when decrypting, signing messages written by the attacker).
- Replace CS Lite with Cookie Monster for cookie management. Cookie Monster has an arguably nicer interface, is being actively maintained and is packaged in Debian.

## Software
- Install MAT, the Metadata Anonymisation Toolkit. Its goal is to remove file metadata which otherwise could leak information about you in the documents and media files you publish. This is the result of a Tails developer's suggestion for GSoC 2011, although it ended up being mentored by The Tor Project.
- Upgrade WhisperBack to 1.5~rc1. Users are guided how to send their bug reports through alternative channels upon errors sending them. This will make bug reporting easier when there's no network connection available.
- Upgrade TrueCrypt to 7.1.

## Miscellaneous
- The date and time setting system was completely reworked. This should prevent time syncing issues that may prevent Tor from working properly, which some users have reported. The new system will not leave a fingerprintable network signature, like the old system did. Previously that signature could be used to identify who is using Tails (but not deanonymize them).
- Erase memory at shutdown: run many instances of the memory wiper. Due to architectural limitations of i386 a process cannot access all memory at the same time, and hence a single memory wipe instance cannot clear all memory.
- Saner keyboard layouts for Arabic and Russian.
- Use Plymouth text-only splash screen at boot time.

Plus the usual bunch of minor bug reports and improvements. The full technical changelog is available.

The full version of this release is available at

Download from here,

October 2011 Progress Report

The October 2011 Progress report is available in PDF and text formats. It contains details of the six major releases, new censorship events in China, and results of a concerted effort to work on hiding Tor's network signature, amongst other progress.

Rumors of Tor's compromise are greatly exaggerated

There are two recent stories claiming the Tor network is compromised. It seems it is easier to get press than to publish research, work with us on the details, and propose solutions. Our comments here are based upon the same stories you are reading. We have no insider information.

The first story has been around 'Freedom Hosting' and their hosting of child abuse materials as exposed by Anonymous Operation Darknet. We're reading the press articles, pastebin urls, and talking to the same people as you. It appears 'Anonymous' cracked the Apache/PHP/MySQL setup at Freedom Hosting and published some, or all, of their users in the database. These sites happened to be hosted on a Tor hidden service. Further, 'Anonymous' used a somewhat recent RAM-exhaustion denial of service attack on the 'Freedom Hosting' Apache server. It's a simple resource starvation attack that can be conducted over low bandwidth, low resource requirement connections to individual hosts. This isn't an attack on Tor, but rather an attack on some software behind a Tor hidden service. This attack was discussed in a thread on the tor-talk mailing list starting October 19th.

The second story is around Eric Filiol's claims of compromising the Tor network leading up to his Hackers to Hackers talk in Brazil in a few days. This claim was initially announced by some French websites; however, it has spread further, such as this Hacker News story.

Again, the tor-talk mailing list had the first discussions of these attacks back on October 13th. To be clear, neither Eric nor his researchers have disclosed anything about this attack to us. They have not talked to us, nor shared any data with us — despite some mail exchanges where we reminded him about the phrase "responsible disclosure".

Here's the attack as we understand it, from reading the various press reports:

They enumerated 6000 IP addresses that they think are Tor relays. There aren't that many Tor relays in the world — 2500 is a more accurate number. We're not sure what caused them to overcount so much. Perhaps they watched the Tor network over a matter of weeks and collected a bunch of addresses that aren't relays anymore? The set of relays is public information, so there's no reason to collect your own list and certainly no reason to end up with a wrong list.

One-third of the machines on those IP addresses are vulnerable to operating system or other system level attacks, meaning he can break in. That's quite a few! We wonder if that's true with the real Tor network, or just their simulated one? Even ignoring the question of what these 3500 extra IP addresses are, it's important to remember that one-third by number is not at all the same as one-third by capacity: Tor clients load-balance over relays based on the relay capacity, so any useful statement should be about how much of the capacity of the Tor network is vulnerable. It would indeed be shocking if one-third of the Tor network by capacity is vulnerable to external attacks.

(There's also an aside about enumerating bridges. They say they found 181 bridges, and then there's a quote saying they "now have a complete picture of the topography of Tor", which is a particularly unfortunate time for that quote since there are currently around 600 bridges running.)

We expect the talk will include discussion about some cool Windows trick that can modify the crypto keys in a running Tor relay that you have local system access to; but it's simpler and smarter just to say that when the attacker has local system access to a Tor relay, the attacker controls the relay.

Once they've broken into some relays, they do congestion attacks like packet spinning to congest the relays they couldn't compromise, to drive users toward the relays they own. It's unclear how many resources are needed to keep the rest of the relays continuously occupied long enough to keep the user from using them. There are probably some better heuristics that clients can use to distinguish between a loaded relay and an unavailable relay; we look forward to learning how well their attack here actually worked.

From there, the attack gets vague. The only hint we have is this nonsense sentence from the article:

The remaining flow can then be decrypted via a fully method of attack called "to clear unknown" based on statistical analysis.

Do they have a new attack on AES, or on OpenSSL's implementation of it, or on our use of OpenSSL? Or are they instead doing some sort of timing attack, where if you own the client's first hop and also the destination you can use statistics to confirm that the two flows are on the same circuit? There's a history of confused researchers proclaiming some sort of novel active attack when passive correlation attacks are much simpler and just as effective.

So the summary of the attack might be "take control of the nodes you can, then congest the other ones so your targets avoid them and use the nodes you control. Then do some unspecified magic crypto attack to defeat the layers of encryption for later hops in the circuit." But really, these are just guesses based on the same news articles you're reading. We look forwarding to finding out if there's actually an attack we can fix, or if they are just playing all the journalists to get attention.

More generally, there are two broader lessons to remember here. First, research into anonymity-breaking attacks is how the field moves forward, and using Tor for your target is common because a) it's resistant to all the simpler attacks and b) we make it really easy to do your research on. And second, remember that most other anonymity systems out there fall to these attacks so quickly and thoroughly that no researchers even talk about it anymore. For some recent examples, see the single-hop proxy discussions in How Much Anonymity does Network Latency Leak? and Website Fingerprinting in Onion Routing Based Anonymization Networks.

I thank Roger, Nick, and Runa for helping with this post.

September 2011 Progress Report

In September 2011 we made progress in a number of areas, such as handling issues in Iran's use of DPI to block tor, new versions of Tor, Tails 0.8 release, and more.

The PDF and plaintext versions of the report can be found attached to this blog post or at our monthly report archive:


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