Mark Menasse has been working on micropayment schemes for a long time now.
He was working on Millicent a while back. Adam Back, the hashcash guy is
also at Microsoft research.
Micropayment schemes do have potential, provided you do not try to actually
transfer or collect the cash and you do not make it your only defense.
If you are C|Net or the like sending out millions of emails a day there is
no micropayment scheme that is going to cost you anything short of millions.
In contrast you can join even the most expensive trusted/bondage sender
accreditation programs for 50 grand or so. A digital certificate with some
sort of authentication to back it up costs $300 to $1000 depending on
application, I don't think that accreditation schemes run in bulk should be
much more expensive.
The economics are more favorable for the small sender. If there is going to
be a meaningful authentication process then there will be a cost. If the
certificate is cheap and easily replaced then it is unlikely to be a
deterent. Trusted sender programs, especially voluntary non profit ones are
currently orders of magnitude more expensive than certificates.
The bottom line is that there is a good chance that a micropayment scheme
that traded some sort of finite or cost bounded resource for the right to
send email can provide value here.
One approach is to use CPU cycles. Another is the velocity indicator
attribute I proposed for a hardware signing device [obs disclosure, there is
a pending patent application]. CPU cycles has the advantage of being easy to
deploy but has the disadvantage of facing Moore's law. The velocity
indicator requires a hardware device but there is no reason these should
cost more than $20. The problem is that they also cannot really cost less,
unless that is the technology is bundled in with some other device (cable
modem, processor, motherboard) in which case the technology becomes a
negligible increase in the cost of item but it is still uneconomic for a
spammer to buy hundreds of PCs just to exhaust the velocity indicator
capacity on each one...
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