Linear combinations are not just for obfuscation any more

Network coding applied to P2P content distribution, as seen in Microsoft’s Avalanche research paper, is motivated by network performance improvement: it makes good use of available network throughput by filling the pipes with data that is useful to others, while avoiding the difficult problem of selecting what your downstream peers will need. Nodes send linear combinations of everything they’ve got, and receivers can reconstruct what they need from that.

There are interesting implications for content filterers. Previously one could argue that transmitting combined blocks (e.g. XOR a file with the U.S. Declaration of Independence, the Constitution, and today’s Dilbert) is purely an obfuscation technique for easily evading content recognizers. Now those techniques will be a basic component of efficiently using available bandwidth, with a side effect of making content recognition and filtering more dynamic and more difficult.

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