Re: [Wikimedia-l] Disinformation regarding perfect forward secrecy for HTTPS
On Fri, Aug 2, 2013 at 7:23 PM, Anthony wikim...@inbox.org wrote: On Fri, Aug 2, 2013 at 10:07 PM, Anthony wikim...@inbox.org wrote: Anthony wrote: How much padding is already inherent in HTTPS? None, which is why Ryan's Google Maps fingerprinting example works. Citation needed. Also please address https://en.wikipedia.org/wiki/Block_cipher_modes_of_operation#Padding It seems that the ciphers which run in CBC mode, at least, are padded. Wikipedia currently seems to be set to use RC4 128. I'm not sure what, if any, padding is used by that cipher. But presumably Wikipedia will switch to a better cipher if Wikimedia cares about security. We're currently have RC4 and AES ciphers in our list, but have RC4 listed first and have a server preference list to combat BEAST. TLS 1.1/1.2 are enabled and I'll be adding the GCM ciphers to the beginning of the list either during Wikimania or as soon as I get back. - Ryan ___ Wikimedia-l mailing list Wikimedia-l@lists.wikimedia.org Unsubscribe: https://lists.wikimedia.org/mailman/listinfo/wikimedia-l, mailto:wikimedia-l-requ...@lists.wikimedia.org?subject=unsubscribe
Re: [Wikimedia-l] Disinformation regarding perfect forward secrecy for HTTPS
On Sat, Aug 3, 2013 at 4:19 AM, Ryan Lane rl...@wikimedia.org wrote: On Fri, Aug 2, 2013 at 7:23 PM, Anthony wikim...@inbox.org wrote: It seems that the ciphers which run in CBC mode, at least, are padded. Wikipedia currently seems to be set to use RC4 128. I'm not sure what, if any, padding is used by that cipher. But presumably Wikipedia will switch to a better cipher if Wikimedia cares about security. We're currently have RC4 and AES ciphers in our list, but have RC4 listed first and have a server preference list to combat BEAST. TLS 1.1/1.2 are enabled and I'll be adding the GCM ciphers to the beginning of the list either during Wikimania or as soon as I get back. Rereading that it looks like I might have implied that Wikimedia didn't care about security. That was absolutely not my intended implication. Sorry about that. ___ Wikimedia-l mailing list Wikimedia-l@lists.wikimedia.org Unsubscribe: https://lists.wikimedia.org/mailman/listinfo/wikimedia-l, mailto:wikimedia-l-requ...@lists.wikimedia.org?subject=unsubscribe
Re: [Wikimedia-l] Disinformation regarding perfect forward secrecy for HTTPS
On Sat, Aug 3, 2013 at 4:19 AM, Ryan Lane rl...@wikimedia.org wrote: We're currently have RC4 and AES ciphers in our list, but have RC4 listed first and have a server preference list to combat BEAST. TLS 1.1/1.2 are enabled and I'll be adding the GCM ciphers to the beginning of the list either during Wikimania or as soon as I get back If possible, could a quick announcement be made (either here or on wikitech or on bug 52496), when we start supporting GCM? Much appreciated. *-- * *Tyler Romeo* Stevens Institute of Technology, Class of 2016 Major in Computer Science www.whizkidztech.com | tylerro...@gmail.com ___ Wikimedia-l mailing list Wikimedia-l@lists.wikimedia.org Unsubscribe: https://lists.wikimedia.org/mailman/listinfo/wikimedia-l, mailto:wikimedia-l-requ...@lists.wikimedia.org?subject=unsubscribe
Re: [Wikimedia-l] Disinformation regarding perfect forward secrecy for HTTPS
On Aug 1, 2013, at 10:07 PM, Ryan Lane rl...@wikimedia.org wrote: Also, our resources are delivered from a number of urls (upload, bits, text) making it easier to identify resources. Even with padding you can take the relative size of resources being delivered, and the order of those sizes and get a pretty good idea of the article being viewed. If there's enough data you may be able to identify multiple articles and see if the subsequent article is a link from the previous article, making guesses more accurate. It only takes a single accurate guess for an edit to identify an editor and see their entire edit history. Proper support of pipelining in browsers or multiplexing in protocols like SPDY would help this situation. There's probably a number of things we can do to improve the situation without pipelining or newer protocols, and we'll likely put some effort into this front. I think this takes priority over PFS as PFS isn't helpful if decryption isn't necessary to track browsing habits. This needs some proper crypto expert vetting, but... It would be trivial (both in effort and impact on customer bandwidth) to pad everything to a 1k boundary on https transmission once we get there. A variable length non-significant header field can be used. Forcing such size counts into very large bins will degrade fingerprinting significantly. It would also not be much more effort or customer impact to pad to the next larger 1k size for a random large fraction of transmissions. One could imagine a user setting where one could opt in or out of that, for example, and perhaps a set of relative inflation scheme sizes one could choose from (10% inflated, 25% inflated, 50%, 50% plus 10% get 1-5 more k of padding, ...). Even the slightest of these options (under https everywhere) starts to give plausible deniability to someone's browsing; the greater ones would make fingerprinting quite painful, though running a statistical exercise of such options to see how hard it would make it seems useful to understand the effects... The question is, what is the point of this? Provide very strong user obfuscation? Provide at least minimal individual evidentiary obfuscation from the level of what a US court (for example) might consider scientifically reliable, to block use of that history in trials (even if educated guesses still might be made by law enforcement as to the articles)? Countermeasures are responses to attain specific goals. What are the goals people care about for such a program, and what are the Foundation willing to consider worth supporting with bandwidth $$ or programmer time? How do we come up with a list of possible goals and prioritize amongst them in both a technical and policy/goals sense? I believe that PFS will come out higher here as it's cost is really only CPU crunchies and already existent software settings to choose from, and its benefits to long term total obscurability are significant if done right. No quantity of countermeasures beat inside info, and out-of-band compromise of our main keys ends up being attractive enough as the only logical attack once we start down this road at all past HTTPS-everywhere. One time key compromise is far more likely than realtime compromise of PFS keys as they rotate, though even that is possible given sufficiently motivated successful stealthy subversion. The credible ability to in the end be confident that's not happening is arguably the long term ceiling for how high we can realistically go with countermeasures, and contains operational security and intrusion detection features as its primary limits rather than in-band behavior. At some point the ops team would need a security team, an IDS team, and a counterintelligence team to watch the other teams, and I don't know if the Foundation cares that much or would find operating that way to be a more comfortable moral and practical stance... George William Herbert Sent from my iPhone ___ Wikimedia-l mailing list Wikimedia-l@lists.wikimedia.org Unsubscribe: https://lists.wikimedia.org/mailman/listinfo/wikimedia-l, mailto:wikimedia-l-requ...@lists.wikimedia.org?subject=unsubscribe
Re: [Wikimedia-l] Disinformation regarding perfect forward secrecy for HTTPS
George William Herbert wrote: ... It would also not be much more effort or customer impact to pad to the next larger 1k size for a random large fraction of transmissions. Padding each transmission with a random number of bytes, up to say 50 or 100, might provide a greater defense against fingerprinting while saving massive amounts of bandwidth. ... At some point the ops team would need a security team, an IDS team, and a counterintelligence team to watch the other teams, and I don't know if the Foundation cares that much or would find operating that way to be a more comfortable moral and practical stance... I'm absolutely sure that they do care enough to get it right, but I think that approach might be overkill. Just one or two cryptology experts to make the transition to HTTPS, PFS, and whatever padding is prudent would really help. I also hope that, if there is an effort to spread disinformation about the value of such techniques, that the Foundation might consider joining with e.g. the EFF to help fight it. I think it's likely that a single cryptology consultant would probably be able to make great progress in both. Getting cryptography right isn't so much as a time-intensive task as it is sensitive to experience and training. Setting up and monitoring with ongoing auditing can often be automated, but does require the continued attention of at least one highly skilled expert, and preferably more than one in case the first one gets hit by a bus. ___ Wikimedia-l mailing list Wikimedia-l@lists.wikimedia.org Unsubscribe: https://lists.wikimedia.org/mailman/listinfo/wikimedia-l, mailto:wikimedia-l-requ...@lists.wikimedia.org?subject=unsubscribe
Re: [Wikimedia-l] Disinformation regarding perfect forward secrecy for HTTPS
On Fri, Aug 2, 2013 at 1:32 PM, James Salsman jsals...@gmail.com wrote: George William Herbert wrote: ... It would also not be much more effort or customer impact to pad to the next larger 1k size for a random large fraction of transmissions. Padding each transmission with a random number of bytes, up to say 50 or 100, might provide a greater defense against fingerprinting while saving massive amounts of bandwidth. Or it might provide virtually no defense and not save any bandwidth. ___ Wikimedia-l mailing list Wikimedia-l@lists.wikimedia.org Unsubscribe: https://lists.wikimedia.org/mailman/listinfo/wikimedia-l, mailto:wikimedia-l-requ...@lists.wikimedia.org?subject=unsubscribe
Re: [Wikimedia-l] Disinformation regarding perfect forward secrecy for HTTPS
On 08/02/2013 01:32 PM, James Salsman wrote: Padding each transmission with a random number of bytes, up to say 50 or 100, might provide a greater defense against fingerprinting while saving massive amounts of bandwidth. It would slightly change the algorithm used to make the fingerprint, not make it any significantly higher, and you'd want to have some fuzz in the match process anyways since you wouldn't necessarily want to have to fiddle with your database at every edit. The combination of at least this size with at least that many secondary documents of at least those sizes in that order is probably sufficient to narrow the match to a very tiny minority of articles. You'd also need to randomize delays, shuffle load order, load blinds, etc. A minor random increase of size in document wouldn't even slow down the process. -- Marc ___ Wikimedia-l mailing list Wikimedia-l@lists.wikimedia.org Unsubscribe: https://lists.wikimedia.org/mailman/listinfo/wikimedia-l, mailto:wikimedia-l-requ...@lists.wikimedia.org?subject=unsubscribe
Re: [Wikimedia-l] Disinformation regarding perfect forward secrecy for HTTPS
How much padding is already inherent in HTTPS? Does the protocol pad to the size of the blocks in the block cipher? Seems to me that any amount of padding is going to give little bang for the buck, at least without using some sort of pipelining. You could probably do quite a bit if you redesigned Mediawiki from scratch using all those newfangled asynchronous javascript techniques, but that's not exactly an easy task. :) On Fri, Aug 2, 2013 at 3:45 PM, Marc A. Pelletier m...@uberbox.org wrote: On 08/02/2013 01:32 PM, James Salsman wrote: Padding each transmission with a random number of bytes, up to say 50 or 100, might provide a greater defense against fingerprinting while saving massive amounts of bandwidth. It would slightly change the algorithm used to make the fingerprint, not make it any significantly higher, and you'd want to have some fuzz in the match process anyways since you wouldn't necessarily want to have to fiddle with your database at every edit. The combination of at least this size with at least that many secondary documents of at least those sizes in that order is probably sufficient to narrow the match to a very tiny minority of articles. You'd also need to randomize delays, shuffle load order, load blinds, etc. A minor random increase of size in document wouldn't even slow down the process. -- Marc ___ Wikimedia-l mailing list Wikimedia-l@lists.wikimedia.org Unsubscribe: https://lists.wikimedia.org/mailman/listinfo/wikimedia-l, mailto:wikimedia-l-requ...@lists.wikimedia.org?subject=unsubscribe ___ Wikimedia-l mailing list Wikimedia-l@lists.wikimedia.org Unsubscribe: https://lists.wikimedia.org/mailman/listinfo/wikimedia-l, mailto:wikimedia-l-requ...@lists.wikimedia.org?subject=unsubscribe
Re: [Wikimedia-l] Disinformation regarding perfect forward secrecy for HTTPS
Marc A. Pelletier wrote: ... A minor random increase of size in document wouldn't even slow down [fingerprinting.] That's absolutely false. The last time I measured the sizes of all 9,625 vital articles, there was only one at the median length of 30,356 bytes but four articles up to 50 bytes larger. Scale that up to 4,300,000 articles, and are you suggesting anyone is seriously going to try fingerprinting secondary characteristics for buckets of 560 articles? It would not only slow them down, it would make their false positive rate useless. This is why we need cryptography experts instead of laypeople making probabilistic inferences on Boolean predicates. Marc, I note that you have recommending not keeping the Perl CPAN modules up to date on Wikimedia Labs: http://www.mediawiki.org/w/index.php?title=Wikimedia_Labs/Tool_Labs/Needed_Toolserver_featuresdiff=678902oldid=678746 saying that out of date packages are the best tested when in fact almost all CPAN packages have their own unit tests. That sort of reasoning is certain to allow known security vulnerabilities to persist when they could easily be avoided. Anthony wrote: How much padding is already inherent in HTTPS? None, which is why Ryan's Google Maps fingerprinting example works. ... Seems to me that any amount of padding is going to give little bang for the buck Again, can we please procure expert opinions instead of relying on the existing pool of volunteer and staff opinions, especially when there is so much FUD prevalent discouraging the kinds of encryption which would most likely strengthen privacy? ___ Wikimedia-l mailing list Wikimedia-l@lists.wikimedia.org Unsubscribe: https://lists.wikimedia.org/mailman/listinfo/wikimedia-l, mailto:wikimedia-l-requ...@lists.wikimedia.org?subject=unsubscribe
Re: [Wikimedia-l] Disinformation regarding perfect forward secrecy for HTTPS
On 08/02/2013 05:06 PM, James Salsman wrote: Marc, I note that you have recommending not keeping the Perl CPAN modules up to date on Wikimedia Labs: http://www.mediawiki.org/w/index.php?title=Wikimedia_Labs/Tool_Labs/Needed_Toolserver_featuresdiff=678902oldid=678746 saying that out of date packages are the best tested when in fact almost all CPAN packages have their own unit tests. That sort of reasoning is certain to allow known security vulnerabilities to persist when they could easily be avoided. Besides being from a few months ago, and unrelated to this conversation, I think that's a mis-characterization of what he said. He said in general he would lean towards keeping the distribution's versions since those are the better tested ones, but noted it should be looked at on a package-by-package basis, and that there may well be good reasons to bump up to a more recent version (a security vulnerability that the distro isn't fixing rapidly enough would be such a reason). It seems from the context better tested meant something like people are using this in practice in real environments, not only automated testing. Matt Flaschen ___ Wikimedia-l mailing list Wikimedia-l@lists.wikimedia.org Unsubscribe: https://lists.wikimedia.org/mailman/listinfo/wikimedia-l, mailto:wikimedia-l-requ...@lists.wikimedia.org?subject=unsubscribe
Re: [Wikimedia-l] Disinformation regarding perfect forward secrecy for HTTPS
On 08/02/2013 05:50 PM, Matthew Flaschen wrote: It seems from the context better tested meant something like people are using this in practice in real environments, not only automated testing. And, indeed, given the constraints and objectives of the Tool Labs (i.e.: no secrecy, all open source and data, high reliability), the more important concern is tested to be robust; I'd deviate from distribution packaging in the case where a security issue could lead to escalation, but concerns about data leaks are not an issue. And whilst I am not a cryptography expert (depending, I suppose, how to define expert) I happen to be very well versed in security protocol design and zero-information analysis (but lack the math acument for cryptography proper so I have to trust the Blums and Shamirs of this world at their word). For what concerns us here in traffic analysis, TLS is almost entirely worthless *on its own*. It is a necessary step, and has a great number of /other/ benefits that justify its deployment without having anything to do with the NSA's snooping. I was not making an argument against it. What I /am/ saying, OTOH, is that random padding without (at least) pipelining and placards *is* worthless to protect against traffic analysis since any reliable method to do it would be necessarily robust against deviation in size. Given that it has a cost to implement and maintain, and consumes resources, it would be counterproductive to do that. It would give false reassurance of higher security without actually bringing any security benefit. I.e.: theatre. -- Marc ___ Wikimedia-l mailing list Wikimedia-l@lists.wikimedia.org Unsubscribe: https://lists.wikimedia.org/mailman/listinfo/wikimedia-l, mailto:wikimedia-l-requ...@lists.wikimedia.org?subject=unsubscribe
Re: [Wikimedia-l] Disinformation regarding perfect forward secrecy for HTTPS
... random padding without (at least) pipelining and placards *is* worthless to protect against traffic analysis No, that is not true, and http://www.ieee-security.org/TC/SP2012/papers/4681a332.pdf explains why. Padding makes it difficult but not impossible to distinguish between two HTTPS destinations. 4,300,000 destinations is right out. since any reliable method to do it would be necessarily robust against deviation in size That's like saying any reliable method to solve satisfiability in polynomial time would be necessarily robust against variations in the number of terms per expression. It's not even wrong. When is the Foundation going to obtain the expertise to protect readers living under regimes which completely forbid HTTPS access to Wikipedia, like China? I suppose I better put that bug about steganography for the surveillance triggers from TOM-Skype in bugzilla. I wish that could have happened before everyone goes to Hong Kong. ___ Wikimedia-l mailing list Wikimedia-l@lists.wikimedia.org Unsubscribe: https://lists.wikimedia.org/mailman/listinfo/wikimedia-l, mailto:wikimedia-l-requ...@lists.wikimedia.org?subject=unsubscribe
Re: [Wikimedia-l] Disinformation regarding perfect forward secrecy for HTTPS
On 08/02/2013 08:15 PM, James Salsman wrote: No, that is not true, and http://www.ieee-security.org/TC/SP2012/papers/4681a332.pdf explains why. Padding makes it difficult but not impossible to distinguish between two HTTPS destinations. 4,300,000 destinations is right out. ... have you actually /read/ that paper? Not only does it discuss how naive countermeasures like you suggest aren't even able to protect against identification at that coarse level, they are presuming much *less* available data to make a determination than what is readily available from visiting /one/ article (let alone what extra information you can extract from one or two consecutive articles because of the correlation provided by the links). Traffic analysis is a hard attack to protect against, and just throwing random guesses at what makes it harder is not useful (and yes, padding is just a random guess that is /well known/ in the litterature to not help against TA despite its benefits in certain kinds of known plaintext and feedback ciphers). I recommend you read ''Secure Transaction Protocol Analysis: Models and Applications'', by Chen et al (ISBN 9783540850731). It's already a little out of date and a bit superficial, but will give you a good basic working knowledge of the problem set and some viable approaches to the subject. -- Marc ___ Wikimedia-l mailing list Wikimedia-l@lists.wikimedia.org Unsubscribe: https://lists.wikimedia.org/mailman/listinfo/wikimedia-l, mailto:wikimedia-l-requ...@lists.wikimedia.org?subject=unsubscribe
Re: [Wikimedia-l] Disinformation regarding perfect forward secrecy for HTTPS
Marc A. Pelletier wrote: ... http://www.ieee-security.org/TC/SP2012/papers/4681a332.pdf ... have you actually /read/ that paper? Of course I have. Have you read the conclusions at the bottom right of page 344? What kind of an adversary trying to infer our readers' article selections is going to be able to use accuracy 10% better than a coin flip? The National Pointless Trial Attorney's Employment Security Agency? ___ Wikimedia-l mailing list Wikimedia-l@lists.wikimedia.org Unsubscribe: https://lists.wikimedia.org/mailman/listinfo/wikimedia-l, mailto:wikimedia-l-requ...@lists.wikimedia.org?subject=unsubscribe
Re: [Wikimedia-l] Disinformation regarding perfect forward secrecy for HTTPS
Anthony wrote: How much padding is already inherent in HTTPS? None, which is why Ryan's Google Maps fingerprinting example works. Citation needed. ... Seems to me that any amount of padding is going to give little bang for the buck Again, can we please procure expert opinions instead of relying on the existing pool of volunteer and staff opinions, especially when there is so much FUD prevalent discouraging the kinds of encryption which would most likely strengthen privacy? Feel free. But don't talk about what is most likely if you're not interested in being told that you're wrong. ___ Wikimedia-l mailing list Wikimedia-l@lists.wikimedia.org Unsubscribe: https://lists.wikimedia.org/mailman/listinfo/wikimedia-l, mailto:wikimedia-l-requ...@lists.wikimedia.org?subject=unsubscribe
Re: [Wikimedia-l] Disinformation regarding perfect forward secrecy for HTTPS
On Fri, Aug 2, 2013 at 10:07 PM, Anthony wikim...@inbox.org wrote: Anthony wrote: How much padding is already inherent in HTTPS? None, which is why Ryan's Google Maps fingerprinting example works. Citation needed. Also please address https://en.wikipedia.org/wiki/Block_cipher_modes_of_operation#Padding It seems that the ciphers which run in CBC mode, at least, are padded. Wikipedia currently seems to be set to use RC4 128. I'm not sure what, if any, padding is used by that cipher. But presumably Wikipedia will switch to a better cipher if Wikimedia cares about security. ___ Wikimedia-l mailing list Wikimedia-l@lists.wikimedia.org Unsubscribe: https://lists.wikimedia.org/mailman/listinfo/wikimedia-l, mailto:wikimedia-l-requ...@lists.wikimedia.org?subject=unsubscribe
Re: [Wikimedia-l] Disinformation regarding perfect forward secrecy for HTTPS
please address https://en.wikipedia.org/wiki/Block_cipher_modes_of_operation#Padding Sure. As soon as someone creates http://en.wikipedia.org/wiki/Sunset_Shimmerso I can use an appropriate example. ___ Wikimedia-l mailing list Wikimedia-l@lists.wikimedia.org Unsubscribe: https://lists.wikimedia.org/mailman/listinfo/wikimedia-l, mailto:wikimedia-l-requ...@lists.wikimedia.org?subject=unsubscribe
Re: [Wikimedia-l] Disinformation regarding perfect forward secrecy for HTTPS
Anthony, padding in this context means adding null or random bytes to the end of encrypted TCP streams in order to obscure their true length. The process of adding padding is entirely independent of the choice of underlying cipher. In this case, however, we have been discussing perfect forward secrecy, which is dependent on the particular cypher. ECDHE-RSA-RC4-SHA is an example of a PFS cipher and TLS key exchange protocol choice widely supported by Apache supporting PFS. The English Wikipedia articles on these subjects are all mostly start-class, so please try Google, Google Scholar, and WP:RX for more information. ___ Wikimedia-l mailing list Wikimedia-l@lists.wikimedia.org Unsubscribe: https://lists.wikimedia.org/mailman/listinfo/wikimedia-l, mailto:wikimedia-l-requ...@lists.wikimedia.org?subject=unsubscribe
Re: [Wikimedia-l] Disinformation regarding perfect forward secrecy for HTTPS
On Fri, Aug 2, 2013 at 11:09 PM, James Salsman jsals...@gmail.com wrote: Anthony, padding in this context means adding null or random bytes to the end of encrypted TCP streams in order to obscure their true length. The process of adding padding is entirely independent of the choice of underlying cipher. My point is that if the stream is encrypted using a block cipher (at least, in CBC mode), then it's already padded to the block size of the cipher. That's the more complete answer to my question of How much padding is already inherent in HTTPS? HTTPS itself does not have any inherent padding, but when used with certain block ciphers, it does. By the way, for most hours it's around 2.1-2.3 million, not 4.3 million. Wikimedia has been kind enough to give us a list of which pages are viewed each hour of the day, along with the size of each page: http://dumps.wikimedia.org/other/pagecounts-raw/ In this case, however, we have been discussing perfect forward secrecy, which is dependent on the particular cypher. ECDHE-RSA-RC4-SHA is an example of a PFS cipher and TLS key exchange protocol choice widely supported by Apache supporting PFS. PFS is the method of key exchange. You can use it with various different ciphers. From what I'm reading it can be used with AES and CBC, which would be a block cipher which pads to 128 or 256 bytes. ___ Wikimedia-l mailing list Wikimedia-l@lists.wikimedia.org Unsubscribe: https://lists.wikimedia.org/mailman/listinfo/wikimedia-l, mailto:wikimedia-l-requ...@lists.wikimedia.org?subject=unsubscribe
Re: [Wikimedia-l] Disinformation regarding perfect forward secrecy for HTTPS
On Fri, Aug 2, 2013 at 11:33 PM, Anthony wikim...@inbox.org wrote: AES and CBC, which would be a block cipher which pads to 128 or 256 bytes. I mean bits, of course. ___ Wikimedia-l mailing list Wikimedia-l@lists.wikimedia.org Unsubscribe: https://lists.wikimedia.org/mailman/listinfo/wikimedia-l, mailto:wikimedia-l-requ...@lists.wikimedia.org?subject=unsubscribe
[Wikimedia-l] Disinformation regarding perfect forward secrecy for HTTPS
With the NSA revelations over the past months, there has been some very questionable information starting to circulate suggesting that trying to implement perfect forward secrecy for https web traffic isn't worth the effort. I am not sure of the provenance of these reports, and I would like to see a much more thorough debate on their accuracy or lack thereof. Here is an example: http://tonyarcieri.com/imperfect-forward-secrecy-the-coming-cryptocalypse As my IETF RFC coauthor Harald Alvestrand told me: The stuff about 'have to transmit the session key I the clear' is completely bogus, of course. That's what Diffie-Hellman is all about. Ryan Lane tweeted yesterday: It's possible to determine what you've been viewing even with PFS. And no, padding won't help. And he wrote on today's Foundation blog post, Enabling perfect forward secrecy is only useful if we also eliminate the threat of traffic analysis of HTTPS, which can be used to detect a user’s browsing activity, even when using HTTP, citing http://blog.ioactive.com/2012/02/ssl-traffic-analysis-on-google-maps.html It is not at all clear to me that discussion pertains to PFS or Wikimedia traffic in any way. I strongly suggest that the Foundation contract with well-known independent reputable cryptography experts to resolve these questions. Tracking and correcting misinformed advice, perhaps in cooperation with the EFF, is just as important. ___ Wikimedia-l mailing list Wikimedia-l@lists.wikimedia.org Unsubscribe: https://lists.wikimedia.org/mailman/listinfo/wikimedia-l, mailto:wikimedia-l-requ...@lists.wikimedia.org?subject=unsubscribe
Re: [Wikimedia-l] Disinformation regarding perfect forward secrecy for HTTPS
On Thu, Aug 1, 2013 at 1:33 PM, James Salsman jsals...@gmail.com wrote: With the NSA revelations over the past months, there has been some very questionable information starting to circulate suggesting that trying to implement perfect forward secrecy for https web traffic isn't worth the effort. I am not sure of the provenance of these reports, and I would like to see a much more thorough debate on their accuracy or lack thereof. Here is an example: http://tonyarcieri.com/imperfect-forward-secrecy-the-coming-cryptocalypse As my IETF RFC coauthor Harald Alvestrand told me: The stuff about 'have to transmit the session key I the clear' is completely bogus, of course. That's what Diffie-Hellman is all about. Ryan Lane tweeted yesterday: It's possible to determine what you've been viewing even with PFS. And no, padding won't help. And he wrote on today's Foundation blog post, Enabling perfect forward secrecy is only useful if we also eliminate the threat of traffic analysis of HTTPS, which can be used to detect a user’s browsing activity, even when using HTTP, citing http://blog.ioactive.com/2012/02/ssl-traffic-analysis-on-google-maps.html It is not at all clear to me that discussion pertains to PFS or Wikimedia traffic in any way. I strongly suggest that the Foundation contract with well-known independent reputable cryptography experts to resolve these questions. Tracking and correcting misinformed advice, perhaps in cooperation with the EFF, is just as important. Well, my post was reviewed by quite a number of tech staff and no one rebutted my claim. Assuming traffic analysis can be used to determine your browsing habits as they are occurring (which is likely not terribly hard for Wikipedia) then there's no point in forward secrecy because there's no point in decrypting the traffic. It would protect passwords, but people should be changing their passwords occasionally anyway, right? Using traffic analysis it's also likely possible to correlate edits with users as well, based on timings of requests and the public data available for revisions. I'm not saying that PFS is worthless, but I am saying that implementing PFS without first solving the issue of timing and traffic analysis vulnerabilities is a waste of our server's resources. - Ryan ___ Wikimedia-l mailing list Wikimedia-l@lists.wikimedia.org Unsubscribe: https://lists.wikimedia.org/mailman/listinfo/wikimedia-l, mailto:wikimedia-l-requ...@lists.wikimedia.org?subject=unsubscribe
Re: [Wikimedia-l] Disinformation regarding perfect forward secrecy for HTTPS
Ryan Lane wrote: ... Assuming traffic analysis can be used to determine your browsing habits as they are occurring (which is likely not terribly hard for Wikipedia) The Google Maps example you linked to works by building a huge database of the exact byte sizes of satellite image tiles. Are you suggesting that we could fingerprint articles by their sizes and/or the sizes of the images they load? But if so, in your tweet you said padding wouldn't help. But padding would completely obliterate that size information, wouldn't it? ___ Wikimedia-l mailing list Wikimedia-l@lists.wikimedia.org Unsubscribe: https://lists.wikimedia.org/mailman/listinfo/wikimedia-l, mailto:wikimedia-l-requ...@lists.wikimedia.org?subject=unsubscribe
Re: [Wikimedia-l] Disinformation regarding perfect forward secrecy for HTTPS
On Thursday, August 1, 2013, James Salsman wrote: Ryan Lane wrote: ... Assuming traffic analysis can be used to determine your browsing habits as they are occurring (which is likely not terribly hard for Wikipedia) The Google Maps example you linked to works by building a huge database of the exact byte sizes of satellite image tiles. Are you suggesting that we could fingerprint articles by their sizes and/or the sizes of the images they load? Of course. They can easily crawl us, and we provide everything for download. Unlike sites like facebook or google, our content is delivered exactly the same to nearly every user. But if so, in your tweet you said padding wouldn't help. But padding would completely obliterate that size information, wouldn't it? Only Opera has pipelining enabled, so resource requests are serial. Also, our resources are delivered from a number of urls (upload, bits, text) making it easier to identify resources. Even with padding you can take the relative size of resources being delivered, and the order of those sizes and get a pretty good idea of the article being viewed. If there's enough data you may be able to identify multiple articles and see if the subsequent article is a link from the previous article, making guesses more accurate. It only takes a single accurate guess for an edit to identify an editor and see their entire edit history. Proper support of pipelining in browsers or multiplexing in protocols like SPDY would help this situation. There's probably a number of things we can do to improve the situation without pipelining or newer protocols, and we'll likely put some effort into this front. I think this takes priority over PFS as PFS isn't helpful if decryption isn't necessary to track browsing habits. Of course the highest priority is simply to enable HTTPS by default, as it forces the use of traffic analysis or decryption, which is likely a high enough bar to hinder tracking efforts for a while. - Ryan ___ Wikimedia-l mailing list Wikimedia-l@lists.wikimedia.org Unsubscribe: https://lists.wikimedia.org/mailman/listinfo/wikimedia-l, mailto:wikimedia-l-requ...@lists.wikimedia.org?subject=unsubscribe
