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Fixing spam with postageFixing spam with postagePosted Feb 15, 2004 8:07 UTC (Sun) by josh (subscriber, #17465)In reply to: Fixing spam with postage by ekj Parent article: Fixing spam with postage Using a non-trivial calculation is a good idea, but "checksum with these trailing bits" is not a good method, since any such method must be standardized as to how to request the calculation, and once standardized, spammers will be buying "2^20 checksums" CDs for use as lookup tables along with their "1000000 email addresses" CDs. If you scale up the size to where a lookup table doesn't work, non-spammers won't be able to send you an email either. What you need is a problem where any given unit of work is reasonably easy (on the order of a few seconds) to do, there are a huge number of work units so the results cannot be precalculated, and the result of a work unit can be easily verified on the other end.
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