On Memory-Bound Functions for Fighting Spam

      Cynthia Dwork             Andrew Goldberg                 Moni Naor


Consider the following simple technique for combatting junk mail (spam):
    If I don't know you, and you want your e-mail to appear in my inbox,
    then you must attach to your message an easily verified  "
proof of computational effort"
    just for me and just for this message.

If the proof of effort requires, say, 10 seconds to compute on a typical  machine, then the economics of sending spam are radically altered. This Pricing via Processing approach  was originally in 1992 by  Dwork and Naor (see here).   They proposed specific CPU-bound functions for this purpose. Abadi, Burrows, Manasse, and Wobber (NDSS 2003) suggested that, since memory access speeds vary across machines much less than do CPU speeds, memory-bound functions may behave more equitably than CPU-bound functions. We further investigate this intriguing proposal. Specifically, we:

Paper: Postscript , gzipped Postscript.

Recent talk on the subject: ppt

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