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(no subject)
by Georg Koppen 11 Jul '11

11 Jul '11

This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --===============7169121415546917615== Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="------------enig3F72C2734FABE1CB4A827A42" This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enig3F72C2734FABE1CB4A827A42 Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: quoted-printable >> Hmmm... If that is the answer to my questions then there is nothing like >> avoiding getting tracked by exit mixes in the concept offered in the >> blog post. Okay. >=20 > That is not entirely true. Because identifiers would be linked to > top-level urlbar domain, gone are the days where exits could insert an > iframe or web-bug into any arbitrary page and use that to track the > user for the duration of the session, regardless of page view. >=20 > Instead, they would be pushed back to doing some sort of top-level > redirect (which we hope would be way more visible), or maybe not even > that, depending on how we define redirects with respect to > "top-level". >=20 > So no, we are not completely abandoning exits as an adversary with > this threat model. If I'm wrong about something, or you think there > are still attacks exits can perform that we should address somehow, > let me know. See my last mail. >> Another question came to my mind: You seem to be at pains not to break >> parts of the web even in the anon mode even if that boils down to not >> implement features that would better fit the needs for people looking >> for unlinkability (one thing that comes to my mind here would be having >> a context being tab dependent additionally). Why? Why not saying: "This >> is Tor's anon mode. It is meant for people that strive for unlinkability >> and might break some functionality. You may still use Tor in normal or >> private browsing mode though (providing no or less unlinkability on the >> browser level)." Do you think that's not worth the effort as Tor's IP >> unlinkability is enough here (especially combined with the things you >> suggested in the blog post)? I do not know Tor's user base very well but >> could imagine that it contains a lot of users that would like to have >> more unlinkability than the "we do not want to break any (or almost any) >> part of the web for a better anonymity" fraction. >=20 > I wish I had better science to give you here on the trade-off we're > going for, but the reality is that we're best-guessing over a very > complex cost/benefit landscape. That's true. > We do know for a fact that the easier Tor is to use (which includes > installation, configuration, overall intuitiveness/"familiarity", > compatibility, and performance), the more people will use it > regularly. That seems to hold for every piece of software, I guess. > We also know for a fact that the more people use Tor, the better the > baseline privacy, anonymity, and censorship resistance properties all > become. Agreed. > Hence, I tend to make decisions in favor of the usability direction > over minor details, especially ones that don't really prevent bad > actors/adversaries from accomplishing their goals. That is definitely a good approach. But maybe there is research to be done here as well. Just a rough (and in part research) idea that I had in mind while asking you the question above: What about if we first started looking at different services offered in the web whether they can be deployed anonymously *at all* (or maybe more precisely (but not much): that can be deployed in a way that there is either no linkability at all or the linkability is not strong enough to endanger the user) (that would be worth some research, I guess)? We would probably find some services where we had to say: "Well, there is no way to get them used anonymously due to their nature and the power of the companies and/or owners behind them." (Facebook comes here to my mind as a candidate and the Google universe as well due to the power Google has). Should we say we make the Tor anon mode compatible with these services nevertheless (due to usability issues) and abandon stronger anonymity measures? I would say no. Not at all. Rather we should be honest and say: "Dear User, surfing anonymously AND using Facebook does not work. You may use the Tor anon mode for that purpose though but there is a high probability that it breaks functionality." The idea of getting more users due to being not too strict here might be appealing but is not the right decision in the end. I think one has to realize that there are services in the web that are *designed* in a way that one EITHER may use them OR use anonymity services. Sure, the devil is in the details (e.g. there are probably a lot of services that may be usable anonymously but then are accompanied with a certain lack of usability. What about them? Should we decide against usability again or should we loosen our means to provide unlinkability here?) but that does not mean there is no way to find a good solution though. In short (and still roughly): I would like to start thinking from having all means available to surf the web anonymously and then downgrade them piece-by-piece to reach a trade-off between anonymity and usability. Services that may not be used anonymously at all would not trigger such a painful downgrade ("painful" as one usually tries first to hack around existing problems encountering unbelievable design issues and bugs and has to concede finally that it is in the user's interest to exclude that feature (again)). > The need for science especially comes in on the fingerprinting arena. > Some fingerprinting opportunities may not actually be appealing to > adversaries. Some may even appear appealing in theory, but in practice > would be noticeable to the user, too noisy, and/or too error-prone. > Hence I called for more panopticlick-style studies, especially of > Javascript features, in the blog post. Yes, that is definitely a good idea though I tend to avoid them all even if currently no adversary is using them (especially if no usability issue is at stake). First: no one knows whether one did not miss an attacker using this kind of attack vector and second: Getting rid of attack vectors is a good thing per se. Georg --------------enig3F72C2734FABE1CB4A827A42 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.10 (GNU/Linux) iQEcBAEBAgAGBQJOGbUuAAoJEKw9P8jZNrM42sIIAKWwpLB+6Aeu97FMeLwJkI/7 blZ98yMsU8fUchIjrkxeTllUX5gcSuI0PSODaMd0lZFEvkFlMAuudcbnC0GmnEVV DP8KV5j8A/RZnVgbEh18AB/keNojnMo/PneCg0109Say2WWqOvL+tklxA14NvgrJ EQlr/P9tmSkdLtwjq5QBQPOVuGNigPk4em2wuSOo1i+7l65VLpfWLYnNwaBEOoGA /ZOKe4h3KLaXiJhaFpvw4d1BoCGAQC2lHb5724qmiTzdFDRAyigewFPxMy8wjO3H mKdPt/WcKw7NfU6jEY7mYRk1D0v3lttjtx9zLwJxwyYXV0rK/DhNiIlJG0uxX8k= =Y0SW -----END PGP SIGNATURE----- --------------enig3F72C2734FABE1CB4A827A42-- --===============7169121415546917615== Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Disposition: inline _______________________________________________ tor-dev mailing list tor-dev(a)lists.torproject.org https://lists.torproject.org/cgi-bin/mailman/listinfo/tor-dev --===============7169121415546917615==--

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(no subject)
by Georg Koppen 11 Jul '11

11 Jul '11

This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --===============2411481729548231614== Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="------------enigC109D701B963D257C02E88A3" This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enigC109D701B963D257C02E88A3 Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: quoted-printable > However, when performed by the exits, this linkability is a real > concern. Let's think about that. That sounds more like our > responsibility than the browser makers. Now I think I see what Georg > was getting at. We didn't mention this because the blog post was > directed towards the browser makers. Well, my idea was not that sophisticated but yes, it belongs to the passive attacks available to exit mixes I generally had in mind (and I agree that the current domain-based proposal makes it way harder for an active mix attacker). My example used just one session. And I still would claim that even this gives an exit mix means to track users during the 10 minutes (and later if the user happens to get the same exit mix again within the same browsing session). If this is true do you mean that it is just not worth the effort or is to difficult to explain to the user (as it is highly probably that avoiding this kind of tracking implies breaking some functionality in the web (a kind of tab separation would be necessary but not sufficient))? Georg --------------enigC109D701B963D257C02E88A3 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.10 (GNU/Linux) iQEcBAEBAgAGBQJOGaJkAAoJEKw9P8jZNrM47GcH/0yeBG8DCujKgedqr7Ex9rNd LU8gP/P/QXQ8q1htwek65fKTm4w8gmjqz0aWqtxBH4oVKy0TisQyBNXd50x2DIag qJQEDnZYVTzl/DrVVy0bDdvk9+xxfprGpjeWPqNWUCuw/9m8e0QfrSWJagC9nDzn iMsmbboLDUQSNWQAkhJX42fv8xI3uHGZY2an418xX9pcDY7qNLBvsVIhMU+MVvXm 9vsdvH2EAXtFNP/OQHp2iP51jUX1oyY0kE+3jtmMp9OjJXWYzKmYlnC6LBaxEXdD 4C7eWXTnVphFNbiT2NFDtcY1hWtWjdoO1uzR/XpoxDO9Gves8xenVVE5S7tZ44I= =Tz7D -----END PGP SIGNATURE----- --------------enigC109D701B963D257C02E88A3-- --===============2411481729548231614== Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Disposition: inline _______________________________________________ tor-dev mailing list tor-dev(a)lists.torproject.org https://lists.torproject.org/cgi-bin/mailman/listinfo/tor-dev --===============2411481729548231614==--

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Feedback on new Orbot data stats
by Nathan Freitas 06 Jul '11

06 Jul '11

Sathya (our fantastic GSoC 2011 dev) has been working on improving the display of information that we can glean from Tor via the control port interface. You can see the results of his work (including an initial screenshot) so far here: http://gsathya.in/blog/?p=66 We would like feedback from Tor/Vidalia and Orbot users out there on what data from Tor that you feel is useful and necessary both as a general case, and perhaps what might be more relevant in a mobile context. One case to consider is that in mobile, we are constantly losing our IP connection, switching from 2G to 3G to Wifi to no service at all. What information does Tor produce that can help the user understand better the state that Orbot is actually in? We are also trying to consider three modes of display: the main screen "dashboard", a full screen detail view, and background notifications that alert the user to important state changes. Thanks! +n8fr8

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Tech report: An Analysis of Tor Relay Stability
by Karsten Loesing 04 Jul '11

04 Jul '11

Hello tor-dev, I just added a tech report called "An Analysis of Tor Relay Stability" that might be interesting to people here to the metrics website: https://metrics.torproject.org/papers/relay-stability-2011-06-30.pdf >From the introduction: "The Tor network consists of around 2,000 relays and 500 bridges run by volunteers, some of which are on dedicated servers and some on laptops or mobile devices. Obviously, we can expect the relays run on dedicated servers to be more "stable" than those on mobile phones. But it is difficult to draw a line between stable and unstable relays. In most cases it depends on the context which relays count as stable: [...] In this analysis, we use a simulator to resemble how the directory authorities assign the Stable and Guard relay flags. This simulator uses archived directory data to decide when a relay was running and when it failed or was restarted. We further use this simulator to calculate future stability metrics that help us evaluate the quality of a given relay flag assignment. We modify the input parameters to Tor's stability metrics to see whether we can improve how the directory authorities should assign relay flags. The analysis data and simulator used in this report are available on the Tor metrics website at https://metrics.torproject.org/." I also made the simulator code and input data available here: https://metrics.torproject.org/papers.html As always, feedback is highly appreciated! Best, Karsten

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Tor and BGP integration
by Jacob Appelbaum 29 Jun '11

29 Jun '11

Hello from Iceland, Linus invited me to Reykjavik to talk about Tor at the NORDUnet conference and this idea is the result of a bit of feedback from some network operators here. Tor needs a way to be friendly to large network operators who wish to enable exiting to anonymous communication for their networks. These network operators are happy to allow anyone to pass traffic to their relays as entry nodes, middle nodes and even limited exit nodes. Linus and I have been discussing methods of automating this process and of course BGP integration makes a lot of sense. Generally, a network operator has a set of AS numbers for their network blocks and as they want people to connect to many of their services, it helps quite a bit to allow exiting to those services from their own Tor relays. We came up with two main ideas for making this happen. One method would be to write a program where given an AS number and a BGP feed, we parse all of the advertised network blocks and emit exit policy lines that accepts all traffic for the AS. This would allow for a web service similar to BulkExitList.py for network aware exit policy generation and relay operators would simply need to add this to their Tor configs manually. For mostly static networks, a cronjob would be fine and Tor doesn't need to know about AS numbers internally. Another method would be to write a controller that watches for BGP network updates and Tor would add relevant exit policy lines for any configured AS. This would allow any Tor relay to dynamically learn about network changes if it has access to a BGP feed patched into a controller. This could be implemented by adding some configuration options to Tor that let Tor know which AS numbers matter to which router. It may also allow for the router to auto learn it's own likely family network but it lacks any kind of bi-directional confirmation, still it seems useful information to have... It would be fantastic if someone offered a hidden service NORDUNet BGPMon feed. This would help enable the first method of generating network aware exit policies; this would also help with the development of AS awareness in Tor itself. In the future, I imagine that it makes a lot of sense for circuit building to be BGP aware as mere netblocks will not be very useful in an ipv6 world, they're already mostly irrelevant. Anyway, food for thought. Linus and I will probably hack on some of these ideas in the near future. All the best, Jake

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WIN32_WINNT in or/or.h
by Gisle Vanem 28 Jun '11

28 Jun '11

I think that the values for 'WIN32_WINNT' and '_WIN32_WINNT' should be protected against redefinement. Reason: In order for MingW to prototype getaddrinfo() and freeaddrinfo() correctly (in <ws2tcpip.h>), '_WIN32_WINNT' *must* be defined as 0x0501 or higher. or/or.h blindly defines them as 0x0400. So, building with -DHAVE_GETADDRINFO needs _WIN32_WINNT to be set to 0x0501. As of now, MingW would simply fallback to use gethostbyname(). So I think this little patch is in order: --- ..\Git-latest\src\or\or.h Mon Jun 20 23:58:06 2011 +++ or\or.h Tue Jun 21 00:04:42 2011 @@ -23,8 +23,12 @@ #endif #ifdef MS_WINDOWS +#ifndef WIN32_WINNT #define WIN32_WINNT 0x400 +#endif +#ifndef _WIN32_WINNT #define _WIN32_WINNT 0x400 +#endif #define WIN32_LEAN_AND_MEAN #endif ----------------------------- What do you say? --gv

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Proposal 182: Credit Bucket
by Nick Mathewson 28 Jun '11

28 Jun '11

Here's a proposal by Florian and Björn about improving our queueing times. Per usual procedure, I'm sending it here as I put it in the proposals directory. Filename: 182-creditbucket.txt Title: Credit Bucket Author: Florian Tschorsch and Björn Scheuermann Created: 22 Jun 2011 Status: Draft Overview: The following proposal targets the reduction of queuing times in onion routers. In particular, we focus on the token bucket algorithm in Tor and point out that current usage unnecessarily locks cells for long time spans. We propose a non-intrusive change in Tor's design which overcomes the deficiencies. Motivation and Background: Cell statistics from the Tor network [1] reveal that cells reside in individual onion routers' cell queues for up to several seconds. These queuing times increase the end-to-end delay very significantly and are apparently the largest contributor to overall cell latency in Tor. In Tor there exist multiple token buckets on different logical levels. They all work independently. They are used to limit the up- and downstream of an onion router. All token buckets are refilled every second with a constant amount of tokens that depends on the configured bandwidth limits. For example, the so-called RelayedTokenBucket limits relay traffic only. All read data of incoming connections are bound to a dedicated read token bucket. An analogous mechanism exists for written data leaving the onion router. We were able to identify the specific usage and implementation of the token bucket algorithm as one cause for very high (and unnecessary) queuing times in an onion router. We observe that the token buckets in Tor are (surprisingly at a first glance) allowed to take on negative fill levels. This is justified by the TLS connections between onion routers where whole TLS records need to be processed. The token bucket on the incoming side (i.e., the one which determines at which rate it is allowed to read from incoming TCP connections) in particular often runs into non-negligible negative fill levels. As a consequence of this behavior, sometimes slightly more data is read than it would be admissible upon strict interpretation of the token bucket concept. However, the token bucket for limiting the outgoing rate does not take on negative fill levels equally often. Consequently, it regularly happens that somewhat more data are read on the incoming side than the outgoing token bucket allows to be written during the same cycle, even if their configured data rates are the same. The respective cells will thus not be allowed to leave the onion router immediately. They will thus necessarily be queued for at least as long as it takes until the token bucket on the outgoing side is refilled again. The refill interval currently is, as mentioned before, one second -- so, these cells are delayed for a very substantial time. In summary, one could say that the two buckets, on the incoming and outgoing side, work like a double door system and frequently lock cells for a full token bucket refill interval length. General Design: In order to overcome the described problem, we propose the following changes related to the token bucket algorithm. We observe that the token bucket on the outgoing connections with its current design is contra productive in the sense of queuing times. We therefore propose modifications to the token bucket algorithm that will eliminate the "double door effect" discussed above. Let us start from Tor's current approach: Thus, we have a regular token bucket on the reading side with a certain rate and a certain burst size. Let x denote the current amount of tokens in the bucket. On the outgoing side we need something appropriate that monitors and constrains the outgoing rate, but at the same time avoids holding back cells (cf. double door effects) whenever possible. Here we propose something that adopts the role of a token bucket, but realizes this functionality in a slightly different way. We call it a "credit bucket". Like a token bucket, the credit bucket also has a current fill level, denoted by y. However, the credit bucket is refilled in a different way. To understand how it works, let us look at the possible operations: As said, x is the fill level of a regular token bucket on the incoming side and thus gets incremented periodically according to the configured rate. No changes here. If x<=0, we are obviously not allowed to read. If x>0, we are allowed to read up to x bytes of incoming data. If k bytes are read (k<=x), then we update x and y as follows: x = x - k (1) y = y + k (2) (1) is the standard token bucket operation on the incoming side. Whenever data is admitted in, though, an additional operation is performed: (2) allocates the same number of bytes on the outgoing side, which will later on allow the same number of bytes to leave the onion router without any delays. If y + x > -M, we are allowed to write up to y + x + M bytes on the outgoing side, where M is a positive constant. M specifies a burst size for the outgoing side. M should be higher than the number of tokens that get refilled during a refill interval, we would suggest to have M in the order of a few seconds "worth" of data. Now if k bytes are written on the outgoing side, we proceed as follows: If k <= y then y = y - k In this case we use "saved" credits, previously allocated on the incoming side when incoming data has been processed. If k > y then y = 0 and x = x - (k-y) We generated additional traffic in the onion router, so that more data is to be sent than has been read (the credit is not sufficient). We therefore "steal" tokens from the token buffer on the incoming side to compensate for the additionally generated data. This will result in correspondingly less data being read on the incoming side subsequently. As a result of such an operation, the token bucket fill level x on the incoming side may become negative (but it can never fall below -M). If y + x <= -M then outgoing data will be held back. This may lead to double-door effects, but only in extreme cases where the outgoing traffic largely exceeds the incoming traffic, so that the outgoing bursts size M is exceeded. Aside from short-term bursts of configurable size (as with every token bucket), this procedure guarantees that the configured rate may never be exceeded (on the application layer, that is; as with the current implementation, an attacker may easily cause the onion router to arbitrarily exceed the limits on the lower layers). Over time, we never send more data than the configured rate: every sent byte needs a corresponding token on the incoming side; this token must either have been consumed by an incoming byte before (it then became a "credit"), or it is "stolen" from the incoming bucket to compensate for data generated within the onion router. Specific Design Changes: In the following we briefly point out the specific changes that need to be done in Tor's source code. By doing so one can see how non intrusive our modifications are. First we need to address the bucket increment and decrement operations. According to the described logic above, this should be done in the methods connection_bucket_refill and connection_buckets_decrement respectively. In particular allocating, saving and "stealing" of tokens need to be considered here. Second the rate limiting, i.e. the amount we are allowed to write (connection_bucket_write_limit) needs to be adapted in lines of the credit bucket logic. Meaning in order to avoid the here identified unnecessary queuing of cells, we need to consider the new burst parameter M. Here we also need to take non rate limited connections such as from the localhost into account. The rate limiting on the reading side remains the same. At last we need to find good values/ ratios for the parameter M such that the trade off between avoiding "double door effects" and maintaining strict rate limits work as expected. As future work and after insights about the performance gain of the here described proposal we need to find a way to implement this both using bufferevent rate limiting with libevent 2.3.x and Tor's rate limiting code. Conclusion: This proposal can be implemented with moderate effort and requires changes only at the points where currently the token bucket operations are performed. We feel that this is not the be-all and end-all solution, because it again introduces a feedback loop between the incoming and the outgoing side. We therefore still hope that we will be able to come to a both simpler and more effective design in the future. However, we believe that what we proposed here is a good compromise between avoiding double-door effects to the furthest possible extent, strictly enforcing an application-layer data rate, and keeping the extent of changes to the code small. Feedback is highly appreciated. References: [1] Karsten Loesing. Analysis of Circuit Queues in Tor. August 25, 2009. [2] https://trac.torproject.org/projects/tor/wiki/sponsors/SponsorD/June2011

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Reg : using the keep alive messages
by Sambuddho Chakravarty 28 Jun '11

28 Jun '11

Hi All I read in the Tor design spec that Tor control protocol supports keepalive messages which could be used for link padding . I wonder if anyone has ever explored using them... Thanks Sambuddho

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TOR control protocol timeout
by Sean Robinson 26 Jun '11

26 Jun '11

Is there a defined timeout for the TOR control protocol? How long should a control port client wait around for socket data when reading? Or writing? The only references to timeouts that I find in control-spec.txt are about circuit and stream timeouts reported back through the control port. -- Sean Robinson WiFi Radar - http://wifi-radar.berlios.de Python WiFi - http://pythonwifi.wikispot.org pymnl - http://pymnl.wikispot.org

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Tor AF independence patch - first big step to Tor IPv6
by Jeroen Massar 21 Jun '11

21 Jun '11

Hi, As this is World IPv6 day, let me present the first big step to Tor IPv6: the Address Family independence Patch ;) https://unfix.org/projects/ipv6/tor/tor-af-independent.diff it is diff against a recent git checkout and should apply more or less cleanly. Why AF independence[1,2] and not "IPv6 patch", well, for a program to be able to support IPv6 it should first not care about IP in the first place. With Tor that is a tricky thing as it actually needs to know about IP for quite a few places. As such this patch primary function is to make most functions use toraddr_t, that way both IPv6 and IPv4 are supported. Note that a lot of functionality for supporting IPv6 (or any other IP protocol in the longer term) is already present in current versions of Tor (even unittests are present already!). Note also that this is not a 'true' AF indepencence patch as in that case we would have to swap toraddr_t with a sockaddr_storage structure, which, when recompiled, would be true AF independent. In the case though that ever a new IP-alike protocol arises and then we still use BSD style sockets, this patch should make it easy to use that new address family too, but don't hold your breath ;) The problem with that though is that at this stage that means that everywhere IPv6 can be stuck just like IPv4 while these should be separate. And to make it a bit worse, one should actually have them also properly in the packets being sent between nodes and there is no separation between exit policies etc. There is thus a lot to discuss on this subject, and one of the first things that really need to be done is ORMultiPort (proposal 118) to be able to separate IPv4 and IPv6 ports. A question there also becomes, do we want to show a Tor node as separate IPv4 and IPv6 routers, or are they to be seen as one, if it is one, we require the above ORMultiport, so that we can have multiple IP addresses and ports on a single node. As such, I suggest we have a big discussion on the flaws of my patch and how to resolve some of the remaining problems and then start moving work to the ORMultPort patch so that we can start enabling IPv6 everywhere, as then we are getting quite close. And maybe, it could be useful to have a special branch on torproject's git server for this, as it is quite a bit of patch ;) Greets, Jeroen (fuzzel on #tor-dev) [1] = http://www.kame.net/newsletter/19980604/ [2] = http://gsyc.escet.urjc.es/~eva/IPv6-web/ipv6.html

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