Sure, you probably slather on the sunscreen when you go to the beach, but what does the discerning BitTorrenter use to protect file transfers from the harsh light of day? Northwestern University researchers suggest "SwarmScreen," their new torrenting obfuscation tool. It's not encryption—and that's the point.

Professors Fabi�n Bustamante, Roger Guimer�, and Luis Amaral assembled a team to look at BitTorrent swarms, and their research revealed something curious: "user connection patterns reveal strong communities." That is, most BitTorrent users actually tend to connect to the same sets of peers, a natural affiliation that arises based on shared interest in films, TV shows, music, or all that legal content The Pirate Bay says it hosts.

Encrypting the transfers would obscure the contents of the files being traded, but it would still reveal the identities of swarm members. As Northwestern describes it, this means that "the patterns of connections—not the data itself—is sufficient to create a powerful threat to user privacy." (In a similar way, deep packet inspection gear can often identity data types, such as P2P traffic, simply by analyzing data "flows," not by peeking into packets or relying on header information.)

Because people tend to group themselves in communities, third parties can "enable a guilt-by-association attack, where an entire community of users can be classified by monitoring one of its members." The research team shows that someone watching BitTorrent can correctly slot a particular user into a "community" with 86 percent accuracy simply by monitoring 1 percent of the network.

Thus, SwarmScreen. The Vuze/Azureus open-source plugin starts a host of random torrents (comprising between 25 percent and 50 percent of a user's BitTorrent activity) to provide "plausible deniability" to BitTorrent users. The random torrents create enough noise in the data that it becomes impossible to sort users into communities.

The recording industry, no doubt gnashing its teeth at such research, will be even less pleased to note that it was all funded by Uncle Sam through a pair of National Science Foundation grants.

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