Tor Traffic Confirmation Attack -Roger Dingledine Report SUMMARY: On July 4 2014 we found a group of relays that we assume were trying to deanonymize users. They appear to have been targeting people who operate or access Tor hidden services. The attack involved modifying Tor protocol headers to do traffic confirmation attacks. The attacking relays joined the network on January 30 2014, and we removed them from the network on July 4. While we don't know when they started doing the attack, users who operated or accessed hidden services from early February through July 4 should assume they were affected. Unfortunately, it's still unclear what "affected" includes. We know the attack looked for users who fetched hidden service descriptors, but the attackers likely were not able to see any application-level traffic (e.g. what pages were loaded or even whether users visited the hidden service they looked up). The attack probably also tried to learn who published hidden service descriptors, which would allow the attackers to learn the location of that hidden service. In theory the attack could also be used to link users to their destinations on normal Tor circuits too, but we found no evidence that the attackers operated any exit relays, making this attack less likely. And finally, we don't know how much data the attackers kept, and due to the way the attack was deployed (more details below), their protocol header modifications might have aided other attackers in deanonymizing users too. Relays should upgrade to a recent Tor release (0.2.4.23 or 0.2.5.6-alpha), to close the particular protocol vulnerability the attackers used -- but remember that preventing traffic confirmation in general remains an open research problem. Clients that upgrade (once new Tor Browser releases are ready) will take another step towards limiting the number of entry guards that are in a position to see their traffic, thus reducing the damage from future attacks like this one. Hidden service operators should consider changing the location of their hidden service. THE TECHNICAL DETAILS: We believe they used a combination of two classes of attacks: a traffic confirmation attack and a Sybil attack. A traffic confirmation attack is possible when the attacker controls or observes the relays on both ends of a Tor circuit and then compares traffic timing, volume, or other characteristics to conclude that the two relays are indeed on the same circuit. If the first relay in the circuit (called the "entry guard") knows the IP address of the user, and the last relay in the circuit knows the resource or destination she is accessing, then together they can deanonymize her. You can read more about traffic confirmation attacks, including pointers to many research papers, at this blog post from 2009: https://blog.torproject.org/blog/one-cell-enough The particular confirmation attack they used was an active attack where the relay on one end injects a signal into the Tor protocol headers, and then the relay on the other end reads the signal. These attacking relays were stable enough to get the HSDir ("suitable for hidden service directory") and Guard ("suitable for being an entry guard") consensus flags: https://gitweb.torproject.org/torspec.git/blob/HEAD:/dir-spec.txt#l1775 Then they injected the signal whenever they were used as a hidden service directory, and looked for an injected signal whenever they were used as an entry guard. The way they injected the signal was by sending sequences of "relay" vs "relay early" commands down the circuit, to encode the message they want to send. For background, Tor has two types of cells: link cells, which are intended for the adjacent relay in the circuit, and relay cells, which are passed to the other end of the circuit. https://gitweb.torproject.org/torspec.git/blob/HEAD:/tor-spec.txt#l364 In 2008 we added a new kind of relay cell, called a "relay early" cell, which is used to prevent people from building very long paths in the Tor network (very long paths can be used to induce congestion and aid in breaking anonymity): http://freehaven.net/anonbib/#congestion-longpaths https://gitweb.torproject.org/torspec.git/blob/HEAD:/proposals/110-avoid-infinite-circuits.txt But the fix for infinite-length paths introduced a problem with accessing hidden services: https://trac.torproject.org/projects/tor/ticket/1038 and one of the side effects of our fix for bug 1038 was that while we limit the number of outbound (away from the client) "relay early" cells on a circuit, we don't limit the number of inbound (towards the client) relay early cells: https://lists.torproject.org/pipermail/tor-commits/2009-July/014679.html So in summary, when Tor clients contacted an attacking relay in its role as a Hidden Service Directory to publish or retrieve a hidden service descriptor (steps 2 and 3 on https://www.torproject.org/docs/hidden-services), that relay would send the hidden service name (encoded as a pattern of relay and relay-early cells) back down the circuit. Other attacking relays, when they get chosen for the first hop of a circuit, would look for inbound relay-early cells (since nobody else sends them) and would thus learn which clients requested information about a hidden service. There are three important points about this attack: A) 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). The encoded signal is encrypted as it is sent over the TLS channel between relays. However, this signal would be easy to read and interpret by anybody who runs a relay and receives the encoded traffic. And we might also worry about a global adversary (e.g. a large intelligence agency) that records Internet traffic at the entry guards and then tries to break Tor's link encryption. The way this attack was performed weakens Tor's anonymity against these other potential attackers too -- either while it was happening or after the fact if they have traffic logs. So if the attack was a research project (i.e. not intentionally malicious), it was deployed in an irresponsible way because it puts users at risk indefinitely into the future. (This concern is in addition to the general issue that it's probably unwise from a legal perspective for researchers to attack real users by modifying their traffic on one end and wiretapping it on the other. Tools like Shadow are great for testing Tor research ideas out in the lab: http://shadow.github.io/ ) B) This protocol header signal injection attack is actually pretty neat from a research perspective, in that it's a bit different from previous tagging attacks which targeted the application-level payload. Previous tagging attacks modified the payload at the entry guard, and then looked for a modified payload at the exit relay (which can see the decrypted payload). Those attacks don't work in the other direction (from the exit relay back towards the client), because the payload is still encrypted at the entry guard. But because this new approach modifies ("tags") the cell headers rather than the payload, every relay in the path can see the tag. C) We should remind readers 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. So the good news is traffic confirmation attacks aren't new or surprising, but the bad news is that they still work. See https://blog.torproject.org/blog/one-cell-enough for more discussion. Then the second class of attack they used, in conjunction with their traffic confirmation attack, was a standard Sybil attack -- they signed up around 115 fast non-exit relays, all running on 220.127.116.11/16 or 18.104.22.168/16. Together these relays summed to about 6.4% of the Guard capacity in the network. Then, in part because of our current guard rotation parameters: https://blog.torproject.org/blog/improving-tors-anonymity-changing-guard-parameters these relays became entry guards for a significant chunk of users over their five months of operation. We actually noticed these relays when they joined the network, since the DocTor scanner reported them: https://lists.torproject.org/pipermail/tor-consensus-health/2014-January/004134.html https://gitweb.torproject.org/doctor.git We considered the set of new relays at the time, and made a decision that it wasn't that large a fraction of the network. It's clear there's room for improvement in terms of how to let the Tor network grow while also ensuring we maintain social connections with the operators of all large groups of relays. (In general having a widely diverse set of relay locations and relay operators, yet not allowing any bad relays in, seems like a hard problem; on the other hand our detection scripts did notice them in this case, so there's hope for a better solution here.) In response, we've taken the following short-term steps: 1) Removed the attacking relays from the network. 2) Put out a software update for relays to prevent "relay early" cells from being used this way. 3) Put out a software update that will (once enough clients have upgraded) let us tell clients to move to using one entry guard rather than three, to reduce exposure to relays over time. 4) Clients can tell whether they've received a relay or relay-cell. For expert users, the new Tor version warns you in your logs if a relay on your path injects any relay-early cells: look for the phrase "Received an inbound RELAY_EARLY cell". The following longer-term research areas remain: 5) Further growing the Tor network and diversity of relay operators, which will reduce the impact from an adversary of a given size. 6) Exploring better mechanisms, e.g. social connections, to limit the impact from a malicious set of relays. We've also formed a group to pay more attention to suspicious relays in the network: https://blog.torproject.org/blog/how-report-bad-relays 7) Further reducing exposure to guards over time, perhaps by extending the guard rotation lifetime: https://blog.torproject.org/blog/lifecycle-of-a-new-relay https://blog.torproject.org/blog/improving-tors-anonymity-changing-guard-parameters 8) Better understanding statistical traffic correlation attacks and whether padding or other approaches can mitigate them. 9) Improving the hidden service design, including making it harder for relays serving as hidden service directory points to learn what hidden service address they're handling: https://blog.torproject.org/blog/hidden-services-need-some-love OPEN QUESTIONS: Q1) Was this the Black Hat 2014 talk that got canceled recently? Q2) Did we find all the malicious relays? Q3) Did the malicious relays inject the signal at any points besides the HSDir position? Q4) What data did the attackers keep, and are they going to destroy it? How have they protected the data (if any) while storing it? Great questions. We spent several months trying to extract information from the researchers who were going to give the Black Hat talk, and eventually we did get some hints from them about how "relay early" cells could be used for traffic confirmation attacks, which is how we started looking for the attacks in the wild. They haven't answered our emails lately, so we don't know for sure, but it seems likely that the answer to Q1 is "yes". In fact, we hope they *were* the ones doing the attacks, since otherwise it means somebody else was. We don't yet know the answers to Q2, Q3, or Q4.
gAtO hEaR _UPDATE-
Sudden rise in direct Tor users
On Tuesday 27th, Roger Dingledine drew attention to the huge increase of Tor clients running . It seems that their number has doubled since August 19th according to the count of directly connecting users . According to Roger this is not just a fluke in the metrics data. The extra load on the directory authorities is clearly visible , but it does not look that the overall network performance are affected so far . The cause is still unknown, but there are already speculations about the Pirate Browser  or the new “anti-piracy” law in Russia which is in force since August, 1st . As Roger pointed out, ?some good solid facts would sure be useful.?
Ever since the the NSA Prism program came out something else is going on in Tor. People want privacy and they will use anything they can to get it. Tor is one solution that a lot of people know about but there are other factors about the increase.
Piratebay.sx and it’s users are doing a lot more stuff with the new browser – There has not been a sustained increase in search traffic for the Pirate Browser on Google. Tor and “Tor browser” haven’t shown a spike in search, either. Could it be from users in Syria? Also note that the Google Play Store has been unblocked in Iran, allowing distribution of Orbot/Orweb in that country to phones with the Play Store app installed (partial bootstrapping problem).
Syria had a spike from 1000 to 4000 but that’s a tiny fraction of the recent increase. Iran doubled from 4000 to 8000 which is also only a part of the increase. Is there a page listing each graph by country or overlapping them all?
The Tor Project also pushed out Orbot v12 to Google Play in the last few weeks – 2 separate updates. That would not account for all of the increase, but it could have prodded enough existing users who had not used Orbot in awhile to start the app up again. We have also seen about 75,000 new installs over the last 3 months.
So we have a lot of factors as the Tor network grows larger everyday– gATo oUt
gAtO fOuNd – this very interesting and wanted to share –
Tor does some things good, but other anonymous networks do other things better. Only when used together do they work best. And of course you want to already know how to use them should something happen to Tor and you are forced to move to another network.
Try them! You may even find something interesting you cannot find on Tor!
These are well known and widely deployed anonymous networks that offer strong anonymity and high security. They are all open source, in active development, have been online for many years and resisted attack attempts. They run on multiple operating systems and are safe to use with default settings. All are well regarded.
- Tor – Fast anonymous internet access, hidden websites, most well known.
- I2P – Hidden websites, anonymous bittorrent, mail, out-proxy to internet, other services.
- Freenet – Static website hosting, distributed file storage for large files, decentralized forums.
Also anonymous networks, but less used and possibly more limited in functionality.
- GnuNet – Anonymous distributed file storage.
- OneSwarm – Bittorrent, has a non-anonymous mode, requires friends for anonymity.
- RetroShare – File-sharing, chat, forums, mail. Requires friends, and not anonymous to those friends, only the rest of the network.
- Omemo – Distributed social storage platform. Uncertain to what extent it is anonymous.
These are anonymous networks, but are not open source. Therefore their security and anonymity properties is hard to impossible to verify, and though the applications are legit, they may have serious weaknesses. Do not rely on them for strong anonymity.
- Osiris – Serverless portal system, does not claim to provide any real anonymity.
- Phantom – Hidden Services, native IPv6 transport.
- GlobaLeaks – Open Source Whistleblowing Framework.
- FreedomBox – Project to create personal servers for distributed social networking, email and audio/video communications.
- Telex – A new way to circumvent Internet censorship.
- Project Byzantium – Bootable live distribution of Linux to set up wireless mesh nodes with commonly available hardware.
- Hyperboria A distributed meshnet built on cjdns.
These are internets overlaid on the internet. They provide security via encryption, but only provides weak to none anonymity on their own. Only standard tools such as OpenVPN and Quagga are required to connect. Responsibility for a sufficiently anonymous setup is placed on the user and their advertised routes. More suited for private groups as things out in the open can be firewalled by other participants. Can be layered above or below other anonymity nets for more security and fun.
- Anonet – AnoNet2, a more open replacement for AnoNet1.
- dn42 – Another highly technical routing community.
- CJDNS, an IPV6 overlay network that provides end to end encryption. It is not anonymous by itself.
- Netsukuku – A project that aims to build a global P2P online network completely independent from the Internet by using Wi-Fi. The software is still in active development, although the site is no longer updated. A new site is in progress of being built.
- Many other wireless communities building mesh networks as an alternative to the Internet, e.g. Freifunk, http://guifi.net and many more around the globe. see also
- Namecoin – Cryptocurrency with the added ability to support a decentralised domain name system currently as a .bit.
- OpenNIC – A user controlled Network Information Center offering a democratic, non-national, alternative to the traditional Top-Level Domain registries.
- Dot-P2P – Another decentralized DNS service without centralized registry operators (at July 18, 2012 page is not accessible and has not known anything about the status of project from February 2011).
gAtO lEaRn – On 01-01-213 we hear that Microsoft buys Skype and makes changes to allow Police surveillance. Then on 01-07-2013 we hear that a professor at the Warsaw University of Technology, Wojciech Mazurczyk, found a way to insert secret 70 bits of data and add secret information similar to steganography.
Lawful Intercept is what it’s called and we just heard punch – counter-punch from the government. I just posted about corporations and governments using offensive cyber weapons to fight crime, but this looks like just plain old spying on citizens like China, Iraq and Syria does. Skype is owned by Microsoft and we know that Word and other products have back doors for them to snoop and governments to use in criminal cases. I guess they do it the proper way and get a real FISA document to monitor us it’s citizens.
mEoW 12-30-2012 our re-elected President Obama signs FISA Warrantless Wiretapping Program. STOP – SAY WHAT. mEoW – Forget about gun control how about the privacy of citizens, are we becoming like China, Iraq and Syria the more I find out about this the crazier it becomes. I hate Skypes but now finding this out NO WAY DUDE-
I did a little digging and I found a document from the Straford hack from the LutzBoat crew and this has been on the play board for a long time. More and more governments that play nice with the America and Microsoft will have to live with the fact that they are spying on us, the people. I voted for Obama but I’m pretty sure any president would want to be able to justify this abuse of power to monitor it’s citizens, what get’s me is we scream and yell when other countries do it but here we are doing to ourselves and nobody is talking about this- Hay press wake up. I have nothing to hide but if you do you have been warned – enjoy your government spying on you behind your back – gAtO oUt
IT security continues to be the greatest challenge facing government CIOs worldwide. Most experts agree that governments require stronger partnerships between the public and private sectors for both better protection of government IT systems from intruders and for greater visibility into operators’ network traffic to fight crime. However, government systems and intelligence activities constitute a very sensitive information environment. Governments must proceed with caution when forming technology partnerships for hardening their IT network security. Melissa E. Hathaway, who in February 2009 was named to be the Obama Administration’s top cyber security official, points out how
Criminals, predators and hackers now use chats, blogs, webmail and Internet applications such as online gaming and file-sharing sites to hide their communications.
Qosmos provides law enforcement agencies with a powerful solution to identify a target using multiple virtual IDs and intercept all related IP- based communications. Any trigger, such as a “user login = target” initiates intercept of all IP traffic related to the “target.”
Example of recognized applications and protocols
VoIP Email (POP, SMTP)
Webmail (Gmail, Hotmail, Live Mail, SquirrelMail, Yahoo mail, etc.)
Instant Messaging (Aim, SNM, Skype, Yahoo, Google Talk, QQ, Maktoob, Paltalk, etc.)
Online games (World of Warcraft)
Online classified ads
Audio/Video (H.323, SIP, MGCP, RTP, RTCP, MMSE, RTSP, SHOUTcast, Yahoo Video,
MSN Video, SCCP, etc.)
Web applications (Dailymotion, Google, eBay, Google Earth, HTTP, MySpace, Wikipedia,
Example of information extracted
Caller, phone number, called party, duration of call
Webmail login, email address, sender, receiver, subject matter, attached documents
Instant messaging sender, receiver, contact lists and status
Forum login, IP address, MAC address, mobile ID (IMSI, IMEI)
Protocols identified even for unidirectional traffic (e.g. email by satellite).
Under the National Operations Center (NOC)’s Media Monitoring Initiative that emerged from the Department of Homeland Security in November, Washington has written permission to collect and retain personal information from journalists, news anchors, reporters or anyone who uses “traditional and/or social media in real time to keep their audience situationally aware and informed.”
According to DHS, the definition of personal identifiable information can consist of any intellect “that permits the identity of an individual to be directly or indirectly inferred, including any information which is linked or linkable to that individual.”
“With this technology, we are trying to give the anti-censorship movement some better tools,” he said.
Until a few days ago, when the joint University of Waterloo and University of Michigan team announced their Telex test running inside a computer lab in Ann Arbor, China’s cyber police may not have known there was a chink in their cyber wall.