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Why Tor Users Should Be Cautious About P2P Privacy 122

An anonymous reader writes "I went across your post a few days ago saying that a machine connected to the Internet was all one needed to spy on most BitTorrent users of the Internet. I followed the link to find out that those researchers from INRIA claimed their attacks also worked for BitTorrent users on Tor. I didn't believe it at first, but then today I found this link on the Tor Project. It seems their attacks don't only link your real IP to your BitTorrent files on Tor but also to the web pages that you're browsing! Tell me it's a joke." No joke, but according to Jacob Appelbaum (a Tor developer), the security flaw is more nuanced — and the fault of software outside of Tor. Read on for his explanation of how the privacy benefits of Tor can be easily lost.
Appelbaum writes "This isn't a failing of Tor, it's a failing of BitTorrent application designers and a privacy failure of their users too. The BitTorrent clients don't appear to double check the information that's ripe for tampering. When combined with common BitTorrent applications that aren't designed for privacy, it's possible to cause a BitTorrent client to leak information about their actual source IP. The BitTorrent protocol is difficult to anonymize with a simple proxy. Ironically, one of the best points of the paper is that those BitTorrent clients also harm the anonymity of the users' web browsing. The user's browsing will often leave the same Tor Exit Node as their BitTorrent traffic; the user is using the same circuit for browsing as they are for BitTorrent. If the user isn't practicing safe browsing techniques, they're probably going to reveal some more of their traffic to the authors of the paper. This is just like the normal internet too. If you browse unsafely, people can observe you or tamper with the data in transit. So in conclusion, this paper isn't about busting anonymity networks as much as it is about busting BitTorrent client privacy." Additionally, he says, "Tor can't keep you anonymous if you don't actually use Tor for your connections. ... The real key is that if they had done transparent proxying (that failed closed) and they had a privacy-aware BT client, the user would probably be fine. Please don't use BitTorrent and Tor together."
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Why Tor Users Should Be Cautious About P2P Privacy

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  • by Anonymous Coward on Friday April 30, 2010 @08:35PM (#32052132)

    Pardon my ignorance, but using Tor for P2P stuff is at best abusive, at worst highly destructive. Tor wasn't designed for high bandwidth applications. It was designed for Web browsing and ensuring that packets from an exit node would be very hard to trace back to the sender as the first priority.

    Of course, even with the best anonymization methods, if someone has cookies, Flash shared objects, or shared objects stored by add-ons that positively identifies their Web browser, their browsing history can be linked together, and some sort of profile be built.

    Tor is half the battle. The second half is making sure your Web browser is anonymous. I prefer running it in a VM which rolls itself back, and has as little customization as possible, so it fits in with the millions of other people running IE with standard XP installs.

  • by santax ( 1541065 ) on Friday April 30, 2010 @08:52PM (#32052262)
    Not everyone uses torrents to download movies... I can even imagine someone trying to watch a recorded news-show or documentary that could get him in trouble... in that case I would say, use of TOR is fine. But in the case of just downloading your average movie, you are right, don't use TOR for that! But there are lots of cases where I feel the use of TOR for torrents is allowed.
  • Using Tor securely (Score:5, Insightful)

    by Dr. Sp0ng ( 24354 ) <.mspong. .at.> on Friday April 30, 2010 @09:08PM (#32052370) Homepage
    There's really only one way to do it - run it on a freshly-installed (probably virtual) machine (so there's no personal data on the system) with a non-public IP address, and then firewall it off so it cannot make any non-Tor network connections. Then apps can leak all the data they want, but they have no useful info to leak.
  • by Anonymous Coward on Friday April 30, 2010 @09:34PM (#32052542)

    uh tor is free so hard for them to invest. you are welcome to donate your bandwidth

  • by Anonymous Coward on Friday April 30, 2010 @09:47PM (#32052636)

    Surrender and go Amish!

  • by Dr. Sp0ng ( 24354 ) <.mspong. .at.> on Friday April 30, 2010 @10:45PM (#32053024) Homepage

    Find Dr. Sp0ng, arrest him, and lock him up.

    Good thing I'm only College-Dropout Sp0ng. They'll never find me.

  • by laird ( 2705 ) <> on Saturday May 01, 2010 @01:55AM (#32054156) Journal

    In case anyone is thinking that this is somehow a 'security flaw' in BitTorrent, we should be clear that privacy is not a design goal of BitTorrent; BitTorrent was designed to provide extremely reliable, efficient file delivery. So while BitTorrent has many strengths (efficiency, etc.) there is a tradeoff between its goals and the goals of a network such as Tor. Specifically, in order to maximize efficiency, BitTorrent distributes your IP address quite openly, has consistent and obvious torrent IDs, etc., which make it efficient and reliable, but pretty much the OPPOSITE of concealing what you are doing from your ISP and the rest of the p2p network. Anyone who was surprised that it's easy to monitor BitTorrent traffic hasn't read the protocol spec - it is EXTREMELY easy to monitor activity in BitTorrent networks, because BitTorrent intentionally distributes everyone's IP addresses, transfer activity, etc., in order to allow the protocol to operate efficiently. So if you want to monitor BitTorrent, you just find tracker addresses and torrent IDs (which are in the .torrent files) and ask the trackers and for the addresses of all of the peers in each torrent, and get back a nice list of peers.

    There are other p2p networks that do attempt to conceal what you are doing in the network, but the cost of that is that they generally are inefficient (wasting tons of CPU and bandwidth) and thus perform badly, making them unpopular with people who want to rapidly download files.

    And I will second the note that running BitTorrent through Tor is a terrible idea. You end up with the worst of both networks - terrible performance and not much security. Worse, doing so damages the rest of the Tor network, interfering with people who are using Tor for what it is designed for.

  • by GlobalColding ( 1239712 ) on Saturday May 01, 2010 @02:24AM (#32054262) Journal
    ... Offer the illusion of privacy.
  • Tor is hopeless (Score:2, Insightful)

    by Animats ( 122034 ) on Saturday May 01, 2010 @02:50AM (#32054340) Homepage

    Tor, as a means of obtaining "privacy", is hopeless. If you use a web browser, the browser headers, cookies, single-pixel GIFs, and Java applets still tend to give out identity information. A sizable fraction of TOR exit points are exploits of one kind or another. Give it up.

  • by santax ( 1541065 ) on Saturday May 01, 2010 @03:53AM (#32054540)
    Yes and when you're in China I am sure the local library will be quite happy to lend you that copy of the dvd on Tankman, just as long as you can show your ID ;)
  • by Anonymous Coward on Saturday May 01, 2010 @08:15AM (#32055330)

    FFS... use Freenet for that, not Tor!

    Tor is preferable if you need low latency; Freenet is preferable for transferring large amounts of data (due to its cache nature).

  • by Bigjeff5 ( 1143585 ) on Saturday May 01, 2010 @11:48AM (#32056454)

    He did not say "Circulate video through bittorrent/tor simply because it's a documentary" or anything like that. It's easy to misread him, but he went out of his way to say he wasn't supporting that.

    You're completely missing why it's a dick move to download torrents on TOR. The AC said exactly why in his post, and everybody has subsequently ignored it.

    Downloading torrents eats away at Tor's bandwidth in large chunks. Tor is a free service, but they have to pay for bandwidth. One person downloading torrents uses the same bandwidth as 100 people or more actively browsing the web. Most people don't actively browse either, they sit on a site and dick around for a while, so it's very possible someone with a high bandwidth connection downloading torrents could use the same bandwidth as several hundred people browsing. This is the same complaint cable companies make, and it's legitimate, but we pay a lot for the service so we tell them to piss off and upgrade their network. Tor is totally different, you are abusing someone's network who is letting you use it for free.

    Ergo, downloading torrents on Tor is a real dick move.

  • by Anonymous Coward on Saturday May 01, 2010 @05:16PM (#32059058)

    Yeah, but Freenet fills a large local cache with child porn, no ifs, ands, or buts about it. Get accused of something, get your HD seized, and good luck explaining to a 60-year-old judge or jury members who likely can't configure their own e-mail clients that you didn't *really* download that stuff.

    TOR carries plenty of nasty material, but it isn't cached locally in such quantities. A cache-heavy tool connected to unknown users intrinsically has some nasty drawbacks.

"My sense of purpose is gone! I have no idea who I AM!" "Oh, my God... You've.. You've turned him into a DEMOCRAT!" -- Doonesbury