Fighting Spam May Be Easier Than You Think

Cynthia Dwork

In CRYPTO'92 Dwork and Naor proposed the following simple technique for combatting 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, then the economics of sending spam are radically altered, as a single machine can send only 8,000 messages per day.

The recent proliferation of spam has lead to a renewed interest in these ideas. This talk surveys recent work on both the choice of functions that can be used to yield easily verifiable proofs of computational effort, and architectures for implementing the proof of effort approach. Filtering and/or forcing senders to pay in other currencies, such as human attention and money, will be covered as time permits.

Gates 4B (opposite 490), 9/24/02, 4:30 PM