February 28, 2024

How BitTorrent Changes the P2P Fight

The big copyright owners have gotten pretty sophisticated about monitoring P2P applications to gather evidence for lawsuits. But now P2P traffic seems to be shifting to the BitTorrent system, which works differently from other P2P systems. This will affect the copyright owners’ monitoring strategy in some interesting ways.

Most P2P systems allow users to choose between being only a receiver of files, and being both a receiver and a provider. (The default is typically to do both.) BitTorrent, by contrast, tries to enforce a kind of reciprocity between its participants, so that you have to provide parts of a file in order to receive other parts. If this works as designed, there is no way to be a passive, receive-only participant in the BitTorrent system. And that fact has important implications.

Copyright owners typically monitor a standard P2P system by joining the system as a receiver. That allows them to see who is providing which files, without requiring them to provide copyrighted files to anybody. If BitTorrent’s reciprocity scheme works, then the copyright owners will have to participate in the P2P distribution of their own copyrighted files in order to monitor who is providing those files. That’s a step they might not be willing to take.

On the other hand, BitTorrent reciprocity will require that ordinary users who want to receive files will have to contribute to the distribution of those files. They won’t have the option of being silent receivers, as they can be on standard P2P systems. Every user will be exposed to detection by the big copyright owners.

This will foil one of the more subtle features of the copyright owners’ P2P strategy. Their decision to monitor and sue the providers of files, but to leave receivers alone, created an incentive for P2P users to shift to receive-only mode. The idea was that if enough users did this, a larger number of receivers would contend for the services of a smaller number of providers, reducing the overall effectiveness of the P2P system. This plan has a certain elegance, but there’s not much evidence it has worked.

These changes are all interesting, but they will happen only so long as the BitTorrent reciprocity mechanism works – only so long as BitTorrent users are actually forced to provide parts of files in order to receive what they want. People who are threatened by these changes – a category that would seem to include the big copyright owners as well as many users of BitTorrent – will have a growing incentive to defeat the reciprocity system so that they can passively monitor BitTorrent, or passively receive files.

My guess is that somebody will figure out how to be a passive BitTorrent user, albeit with lower performance than active providers get. The knowledge of how to do this may change BitTorrent in important ways. If I were a big copyright owner, I might even consider developing releasing a BitTorrent-leech application.

(For more thoughts on copyright owners and BitTorrent, see Cuong Nguyen’s post on CopyFutures.)


  1. David Carroll says

    BitTorrent isn’t quite like a “true” p2p filesharing system. For a file to be made available via BitTorrent, one special computer somewhere is running something called a “tracker“. Everybody who wants to download the file has to connect to the tracker process, which shares out the workload of downloading & uploading chunks of the file. Downloaders discover the tracker by acquiring small “.torrent” files (via web pages or newsgroups or whatever) which include the tracker’s URL or IP address, as well as some hash information about the file.

    It seems to me that copyright owners could easily bring action against the people who set up the tracker. And as soon as it is shut down the torrent swarm will collapse, and a new tracker and “.torrent” files would need to be set up by somebody else. So from a legal point of view BitTorrent distribution looks as easy to interdict as http or ftp distribution.

  2. BitTorrent was not actually designed to forbid people to download without uploading. For one thing, if it were designed that way, it would be very difficulty for anyone to download from a complete downloader (who doesn’t need any parts of the file and therefore can’t be benefitted by anyone offering pieces.

    BitTorrent is designed so that you can maximize your download rate by uploading, but not so that you have to upload in order to get a nonzero download rate. Since BitTorrent follows a tit-for-tat strategy, other clients start out by co-operating even if you start out by defecting. That means you can get a download from them even if you play “all D” (only defect).

    Indeed, after your download is complete, if you permit your client to continue to upload (which is the default behavior), it will provide essentially gratuitous uploads — other clients do not have to do anything at all in order to be permitted to download from you. (I don’t know what algorithm BitTorrent uses in order to decide who gets what kind of download bitrate from you at that point; it might just be random or round-robin. But a “leech” would certainly be able to download the entire file from you at that point without even uploading anything.)

    Bram’s BitTorrent FAQ explains this in the following way:

    You could hack the source to not upload, but then your download rate would suck. BitTorrent downloaders engage in tit-for-tat with their peers, so leeches have very little success downloading.

    Note that he says “would suck” rather than “would be zero” and “have very little success” rather than “have no success”; BitTorrent’s tit-for-tat strategy is an attempt to encourage co-operation rather than to require it.

    While I’m on the subject of the Prisoner’s Dilemma and filesharing, it’s worth mentioning a different point of view on what constitutes co-operation and defection in the file-sharing world. I wonder if DeLong and Singleton are familiar with the design of BitTorrent.

    In terms of suing people for infringing uses of BitTorrent, it’s interesting to consider how disaggregated the functions are in BitTorrent publishing, and hence which particular functions are potentially infringing. I would love to see some copyright lawyers debate that.

  3. on linked blog, I found this story more interesting. it looks like someone found out how to combine p2p with webcast – ie. does not sell or rent music, but perform in public – so under a different licensing regime; and there seems to be a business plan that compensates authors and composers. now how about taping/time or space shifting a show?

  4. on linked blog, I found this story more interesting. it looks like someone found out how to combine p2p with webcast – ie. does not sell or rent music, but perform in public – so under a different licensing regime; and there seems to be a business plan that compensates authors and composers. now how about taping/time or space shifting a show?

  5. http://mute-net.sourceforge.net/ (MUTE) is designed with anonymity and encryption in mind from the start, and makes Big Brother (be it called MPAA, RIAA, CIA, etc.) tracking attempts on p2p transfers much harder to accomplish successfully. Bittorrent is great, but users need to stay smart if they’re doing something that is considered illegal depending in which place or time they live.

  6. Unfortunately, the previous commenters are correct. BitTorrent is certainly not anonymous (as Bram has repeatedly said) and it’s straight forward to find a list of users in a torrent without uploading anything (otherwise, how would you get the first block?)

    Also, if you were suggesting that this may provide a form of legal defense (“I was allow to download this file! Look, the copyright holder was uploading it to me!”) then I really don’t think that that’s going to work either. Few (I don’t know the exact number) of the RIAA case ever reached trial. Its not worth anyone’s while to try to fight them.


  7. Actually, with the way bittorrent works copyright owners would only have to connect to the so-called tracker. The tracker keeps track of which clients are connected and trying to download the file. Each time a new client connects that client gets a list of 20 random IPs from all the clients connected to the tracker. For most trackers, it is possible to ask the tracker how many clients are connected at any time. So a copyright owner only has to connect to the tracker repeatedly until it has a complete or almost complete list of IPs downloading or uploading that file.

    Presumably, they could figure out who is uploading and who is downloading by monitoring the actual bittorrent clients, or actually asking them for parts of the file to see which clients are uploading and which are downloading.

    With bittorrent, copyright owners do not have to transfer or recieve any parts of the file to get a lot of information.

  8. There already are bittorrent clients which permit “leeching”… g3torrent, torrentstorm, bitspirit… as well, I’ve heard that competent coders can build versions of the open source bittorrent clients with no upload capability via spoofing other clients (in some fashion). (I haven’t seen a good newsy or comp. sci. interest piece on BitTorrent leaching that I can point you too… someone else chime-in!)