Christin, Weigend, and Chuang have an interesting new paper on corruption of files in P2P networks. Some files are corrupted accidentally (they call this “pollution”), and some might be corrupted deliberately (“poisoning”) by copyright owners or their agents. The paper measures the availability of popular, infringing files on the eDonkey, Overnet, Gnutella, and FastTrack networks, and simulates the effect of different pollution strategies that might be used.
The paper studied a few popular files for which corruption efforts were not occurring (or at least not succeeding). Polluted versions of these files are found, especially on FastTrack, but these aren’t a barrier to user access because non-corrupted files tend to have more replicas available than polluted files do, and the systems return files with more replicas first.
They move on to simulate the effect of various pollution strategies. They conclude that a sufficiently sophisticated pollution strategy, which injects different decoy versions of a file at different times, and injects many replicas of the same decoy at the same time, would significantly reduce user access to targeted files.
Some P2P programs use simple reputation systems to try to distinguish corrupted files from non-corrupted ones; the paper argues that these will be ineffective against their best pollution strategy. But they also note that better reputation systems could can detect their sophisticated poisoning strategy.
They don’t say anything more about the arms race between reputation technologies and pollution technologies. My guess is that in the long run reputation systems will win, and poisoning strategies will lose their viability. In the meantime, though, it looks like copyright owners have much to gain from poisoning.
[UPDATE (6:45 PM): I changed the second paragraph to eliminate an error that was caused by my misreading of the paper. Originally I said, incorrectly, that the study found little if any evidence of pollution for the files they studied. In fact, they chose those files because they were not subject to pollution. Thanks to Cypherpunk, Joe Hall, and Nicolas Christin for pointing out my error.]