A good summary, John.
Thanks.
Receipient rate limiting might take the form of hashcash, although
that seems too easily circumvented so long as the bad guys have
zombies to do their hashing.
This is a quantitative rather than qualitative argument against
hashcash, which is easily answered by increasing the bit count demanded
by the recipient, if it seems it's not having enough effect.
The problem is that if you increase the bit count demanded from the
bad guys, you also increase the bit count demanded from the good guys.
Since the bad guys have more computers at their disposal than the good
guys do, if you demand a big enough hash from the bad guys to deter
them, you're going to lock out the good guys altogether, e.g., demand
a hash from Aunt Sadie that will limit her 486 to one e-mail message a
week.
You might want to demand larger hashes from bad guys from good guys,
but if you could tell which was which, you could reject the bad guys'
mail outright and dispense with the hashes.
Regards,
John Levine, johnl(_at_)taugh(_dot_)com, Taughannock Networks, Trumansburg NY
http://www.taugh.com
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