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Tor security advisory: “relay early” traffic confirmation attack

197 points by ohmygodel 12y ago

infinity0 12y ago
Please will a mod rename the title? The blog post explicitly says (at the bottom) that we don't know if this is the Black Hat talk that got cancelled early.
- mike-cardwell 12y ago
  Whilst they do say that they don't know, they do also say that it "seems likely", and provide some fairly convincing evidence for that reasoning. But yes, the title doesn't quite reflect that.
  - tptacek 12y ago
    This title made me think, "wow, the Tor team is usually pretty on-the-ball, did they really write a sentence that started with 'Black Hat researchers', as if that was a thing?" It's a truly bad title; it editorializes, it's contradicted by the article ("maybe" is not "affirmatively"), and it confuses its subjects with the venue they happen to present at (think about how nonsensical "ACM researchers do X" or "USENIX researchers do Y" sounds).
    - makomk 12y ago
      Someone posted the same article with the original title on HN earlier and it sank without a trace, whereas this one seems to have stuck. Apparently it's a pretty good title from that perspective.
      - tptacek 12y ago
        Yeah. Stupid honesty. Who needs it?
        psykovsky 12y ago
        You could use some yourself. And maybe some altruism to go with it...
      - DanBC 12y ago
        https://news.ycombinator.com/item?id=8107273 https://news.ycombinator.com/item?id=8107273 which goes to https://lists.torproject.org/pipermail/tor-announce/2014-July/000094.html https://lists.torproject.org/pipermail/tor-announce/2014-Jul...
      - dang 12y ago
        > Apparently it's a pretty good title from that perspective. There's a lot of randomness in which stories get uptake and when.
        scott_s 12y ago
        We need to put that on a tshirt.
- dang 12y ago
  Yes. The submitted title ("Black Hat researchers actively attack Tor users") violated the HN guidelines.
higherpurpose 12y ago
I'm disappointed nobody has "leaked" the research so far. If they cared enough to research it in academia, surely they know it's important enough for Tor developers to know about the type of attacks they were performing, despite what any government officials might say? At least some hints should be leaked, if not the whole research.
- dm2 12y ago
  That wouldn't really be ethical would it? It would do more harm than good, such as get a lot of people arrested, tortured, killed, and discovered as spies. Responsible disclosure is best, get it patched then release the details of the vulnerability.
  - sp332 12y ago
    There is a limit. You're also keeping information from the victims who can't protect themselves without your information.
- _nullandnull_ 12y ago
  You do realize that "leaked" information on the TOR network could cost an activist their life?
- tptacek 12y ago
  Leaking hints is the dumbest conceivable way to handle disclosure. It taunts the community and sets up a race to independently find the flaw. The race happens much more openly than the original research, meaning that flaws are incrementally disclosed, ensuring that bad actors of every skill level will get a crack at the attack before it's fully fixed. Don't ever do this, at least not for a bug that matters. It would be better not to disclose at all than to do this.
mike-cardwell 12y ago
"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."
opendais 12y ago
It sounds like to be truly safe you need to know safe entry guard node(s) and/or operate your own group of entry relays. Otherwise, you risk X% of your traffic potentially being deanonymized by someone controlling both ends. Of course, if you do that, you probably need to remain constantly connected and moving data through Tor 24/7 to prevent any kind of analysis since you can't hide the fact you: A) Control the relay you connect to. B) Are connected to Tor.
- peterwwillis 12y ago
  > you probably need to remain constantly connected and moving data through Tor 24/7 You almost have it. The problem is that just moving data through isn't enough. Given enough sample data, you can eventually figure out enough information about the traffic to correlate with another host moving the same traffic. The most effective way to mask the effects of passive statistical analysis is to employ either a masking effect or a countermeasure. Either make all the traffic look identical (and have its rate be identical and constant), or make all the traffic look random, insofar as garbage is injected or frames are truncated at every hop. Also, you don't have to control both ends. You just have to observe a given percentage of the traffic along its path(s), and you can determine a probability of which hosts lead to/from what traffic. If you're just trying to trace an unknown adversary, it may be able to [at the very least] identify the network they're on.
  - opendais 12y ago
    > Also, you don't have to control both ends. You just have to observe a given percentage of the traffic along its path(s), and you can determine a probability of which hosts lead to/from what traffic. If you're just trying to trace an unknown adversary, it may be able to [at the very least] identify the network they're on. Really? I figured the number of hops involved meant as long as they couldn't control both Entry Guard & Exit Node you were relatively safe. > The most effective way to mask the effects of passive statistical analysis is to employ either a masking effect or a countermeasure. Either make all the traffic look identical (and have its rate be identical and constant), or make all the traffic look random, insofar as garbage is injected or frames are truncated at every hop. So, setup a webcrawler whenever you aren't using it that randomly crawls pages I suppose. Random garbage would make you easier to find, I suspect, since it doesn't fit with a "normal" pattern of any kind. I mostly look at Tor out of curiosity. :)
scottalpert 12y ago
First rule of security: There is no perfect security. You need a multilayered strategy. Tor is a start. Anonymized OSs like Tails are another aspect. Not releasing personal info on the web -- to the extent you can do that -- is another.
- 616c 12y ago
  Ironically only one of my friends has gone that far on the last count. He is an attorney and very persistent, and many of these companies do claim to clean up all his data when he writes letters with the proper legal wording to signal they need to take it seriously. It is time consuming, but these letters paid off. Only one of the scummy German screenscraper sights did not comply, and ignored him. I cannot find him anywhere if not for the email address he sent me years later, and no other mention of life exists.
  - gioele 12y ago
    > I cannot find him anywhere if not for the email address he sent me years later, and no other mention of life exists. I guess his job does not involve participating in projects that have git repositories or public mailing lists.
    - wereHamster 12y ago
      That is just not true. The email address in git does not need to exist. It just has to look like one, you can use for example `anon@example.com`.
      - 616c 12y ago
        Moreover, I know more important and intelligent people than I are interested in such things, but if you want a C++ SCM system that has strong signing and allows for pseudo-anonymous development, check out Monotone. I had trouble using it and building it with Lua 5.2 after core Lua API changes. Nonetheless, it is what the I2P project uses, and i assume they take such things seriously for a reason.
Udo 12y ago
Is this problem even solvable on a fundamental level? Of course, they can work on preventing nodes forwarding hidden header information, but an entity with global network insight will always be able to correlate users by the timing of their transmissions alone. The introduction of malicious nodes is a workable option for lesser players. But hidden in the realtime nature of the Tor network is always the possibility of deanonymizing users if you're a powerful agency that can afford to inspect a sufficiently large part of all network traffic - they don't even have to run any nodes themselves.
- regd006 12y ago
  > but an entity with global network insight will always be able to correlate users by the timing of their transmissions alone. For what it's worth, this type of adversary is explicitly excluded in Tor's threat model[0]. [0] https://svn.torproject.org/svn/projects/design-paper/tor-design.html#subsec:threat-model https://svn.torproject.org/svn/projects/design-paper/tor-des...
- peterwwillis 12y ago
  Sure it is; it's just impractical. If you force the entire network to play by certain timing rules and mangle the traffic in a uniform way it'd be very difficult to analyze the network to discover unique patterns. But this might also make the network impractical to use for anything but Twitter and e-mail.
  - Udo 12y ago
    Which was my point when I referred to the realtime constraint...
- brian_cloutier 12y ago
  Yes, you just have to think about networking a little differently. The problem is that we share documents over connections. Immutable documents don't really need to get to you immediately, especially now that we have webapps with UIs which update instantly and which can perform non-trivial computation. Onion routing with something like Mixminion[1] works much like Tor, but instead of establishing connections it passes messages between routers. Messages are arbitrarily delayed, preventing even traffic analysis from finding you. However, using an anonymous remailer like Mixminion would require completely rethinking browsers and our protocols for web browsing. They simply aren't designed for a world where packets might take minutes to get to you. [1] http://en.wikipedia.org/wiki/Mixminion http://en.wikipedia.org/wiki/Mixminion
deleted 12y ago
[deleted]

197 points by ohmygodel 12y ago

Please will a mod rename the title? The blog post explicitly says (at the bottom) that we don't know if this is the Black Hat talk that got cancelled early.

mike-cardwell 12y ago
Whilst they do say that they don't know, they do also say that it "seems likely", and provide some fairly convincing evidence for that reasoning. But yes, the title doesn't quite reflect that.
- tptacek 12y ago
  This title made me think, "wow, the Tor team is usually pretty on-the-ball, did they really write a sentence that started with 'Black Hat researchers', as if that was a thing?" It's a truly bad title; it editorializes, it's contradicted by the article ("maybe" is not "affirmatively"), and it confuses its subjects with the venue they happen to present at (think about how nonsensical "ACM researchers do X" or "USENIX researchers do Y" sounds).
  - makomk 12y ago
    Someone posted the same article with the original title on HN earlier and it sank without a trace, whereas this one seems to have stuck. Apparently it's a pretty good title from that perspective.
    - tptacek 12y ago
      Yeah. Stupid honesty. Who needs it?
      - psykovsky 12y ago
        You could use some yourself. And maybe some altruism to go with it...
    - DanBC 12y ago
      https://news.ycombinator.com/item?id=8107273 https://news.ycombinator.com/item?id=8107273 which goes to https://lists.torproject.org/pipermail/tor-announce/2014-July/000094.html https://lists.torproject.org/pipermail/tor-announce/2014-Jul...
    - dang 12y ago
      > Apparently it's a pretty good title from that perspective. There's a lot of randomness in which stories get uptake and when.
      - scott_s 12y ago
        We need to put that on a tshirt.
dang 12y ago
Yes. The submitted title ("Black Hat researchers actively attack Tor users") violated the HN guidelines.

higherpurpose 12y ago

I'm disappointed nobody has "leaked" the research so far. If they cared enough to research it in academia, surely they know it's important enough for Tor developers to know about the type of attacks they were performing, despite what any government officials might say? At least some hints should be leaked, if not the whole research.

dm2 12y ago
That wouldn't really be ethical would it? It would do more harm than good, such as get a lot of people arrested, tortured, killed, and discovered as spies. Responsible disclosure is best, get it patched then release the details of the vulnerability.
- sp332 12y ago
  There is a limit. You're also keeping information from the victims who can't protect themselves without your information.
_nullandnull_ 12y ago
You do realize that "leaked" information on the TOR network could cost an activist their life?
tptacek 12y ago
Leaking hints is the dumbest conceivable way to handle disclosure. It taunts the community and sets up a race to independently find the flaw. The race happens much more openly than the original research, meaning that flaws are incrementally disclosed, ensuring that bad actors of every skill level will get a crack at the attack before it's fully fixed. Don't ever do this, at least not for a bug that matters. It would be better not to disclose at all than to do this.

mike-cardwell 12y ago

"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."

opendais 12y ago

It sounds like to be truly safe you need to know safe entry guard node(s) and/or operate your own group of entry relays. Otherwise, you risk X% of your traffic potentially being deanonymized by someone controlling both ends. Of course, if you do that, you probably need to remain constantly connected and moving data through Tor 24/7 to prevent any kind of analysis since you can't hide the fact you: A) Control the relay you connect to. B) Are connected to Tor.

peterwwillis 12y ago
> you probably need to remain constantly connected and moving data through Tor 24/7 You almost have it. The problem is that just moving data through isn't enough. Given enough sample data, you can eventually figure out enough information about the traffic to correlate with another host moving the same traffic. The most effective way to mask the effects of passive statistical analysis is to employ either a masking effect or a countermeasure. Either make all the traffic look identical (and have its rate be identical and constant), or make all the traffic look random, insofar as garbage is injected or frames are truncated at every hop. Also, you don't have to control both ends. You just have to observe a given percentage of the traffic along its path(s), and you can determine a probability of which hosts lead to/from what traffic. If you're just trying to trace an unknown adversary, it may be able to [at the very least] identify the network they're on.
- opendais 12y ago
  > Also, you don't have to control both ends. You just have to observe a given percentage of the traffic along its path(s), and you can determine a probability of which hosts lead to/from what traffic. If you're just trying to trace an unknown adversary, it may be able to [at the very least] identify the network they're on. Really? I figured the number of hops involved meant as long as they couldn't control both Entry Guard & Exit Node you were relatively safe. > The most effective way to mask the effects of passive statistical analysis is to employ either a masking effect or a countermeasure. Either make all the traffic look identical (and have its rate be identical and constant), or make all the traffic look random, insofar as garbage is injected or frames are truncated at every hop. So, setup a webcrawler whenever you aren't using it that randomly crawls pages I suppose. Random garbage would make you easier to find, I suspect, since it doesn't fit with a "normal" pattern of any kind. I mostly look at Tor out of curiosity. :)

scottalpert 12y ago

First rule of security: There is no perfect security. You need a multilayered strategy. Tor is a start. Anonymized OSs like Tails are another aspect. Not releasing personal info on the web -- to the extent you can do that -- is another.

616c 12y ago
Ironically only one of my friends has gone that far on the last count. He is an attorney and very persistent, and many of these companies do claim to clean up all his data when he writes letters with the proper legal wording to signal they need to take it seriously. It is time consuming, but these letters paid off. Only one of the scummy German screenscraper sights did not comply, and ignored him. I cannot find him anywhere if not for the email address he sent me years later, and no other mention of life exists.
- gioele 12y ago
  > I cannot find him anywhere if not for the email address he sent me years later, and no other mention of life exists. I guess his job does not involve participating in projects that have git repositories or public mailing lists.
  - wereHamster 12y ago
    That is just not true. The email address in git does not need to exist. It just has to look like one, you can use for example `anon@example.com`.
    - 616c 12y ago
      Moreover, I know more important and intelligent people than I are interested in such things, but if you want a C++ SCM system that has strong signing and allows for pseudo-anonymous development, check out Monotone. I had trouble using it and building it with Lua 5.2 after core Lua API changes. Nonetheless, it is what the I2P project uses, and i assume they take such things seriously for a reason.

Udo 12y ago

Is this problem even solvable on a fundamental level? Of course, they can work on preventing nodes forwarding hidden header information, but an entity with global network insight will always be able to correlate users by the timing of their transmissions alone. The introduction of malicious nodes is a workable option for lesser players. But hidden in the realtime nature of the Tor network is always the possibility of deanonymizing users if you're a powerful agency that can afford to inspect a sufficiently large part of all network traffic - they don't even have to run any nodes themselves.

regd006 12y ago
> but an entity with global network insight will always be able to correlate users by the timing of their transmissions alone. For what it's worth, this type of adversary is explicitly excluded in Tor's threat model[0]. [0] https://svn.torproject.org/svn/projects/design-paper/tor-design.html#subsec:threat-model https://svn.torproject.org/svn/projects/design-paper/tor-des...
peterwwillis 12y ago
Sure it is; it's just impractical. If you force the entire network to play by certain timing rules and mangle the traffic in a uniform way it'd be very difficult to analyze the network to discover unique patterns. But this might also make the network impractical to use for anything but Twitter and e-mail.
- Udo 12y ago
  Which was my point when I referred to the realtime constraint...
brian_cloutier 12y ago
Yes, you just have to think about networking a little differently. The problem is that we share documents over connections. Immutable documents don't really need to get to you immediately, especially now that we have webapps with UIs which update instantly and which can perform non-trivial computation. Onion routing with something like Mixminion[1] works much like Tor, but instead of establishing connections it passes messages between routers. Messages are arbitrarily delayed, preventing even traffic analysis from finding you. However, using an anonymous remailer like Mixminion would require completely rethinking browsers and our protocols for web browsing. They simply aren't designed for a world where packets might take minutes to get to you. [1] http://en.wikipedia.org/wiki/Mixminion http://en.wikipedia.org/wiki/Mixminion

deleted 12y ago

[deleted]