From: Robert Hettinga <rah@shipwright.com>
Date: Sat, 5 Jul 1997 02:01:12 +0800
To: cypherpunks@toad.com
Subject: e$: $MTP?
Message-ID: <v03020916afe2dea80083@[139.167.130.247]>
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Date:  Fri, 4 Jul 1997 09:21:12 -0400
From: Robert Hettinga <rah@shipwright.com>
To: Multiple recipients of <e$@thumper.vmeng.com>
Subject:  e$: $MTP?

They've been talking on cypherpunks about various ideas for authenticating
the sender of mail, and it brings up something I've been increasing my
agit-prop efforts on lately.

Unfortunately, the ultimate way for any e-mail authentication scheme to
work is for the *whole* message to be signed, headers and all, and then for
the sending SMTP server to sign the message passes it on, headers and all,
and so forth. The consequences of this approach, in terms of machine
resources, not to mention privacy (plus or minus how close you can get to
perfect pseudonymity), will probably be excessive.

The solution, here, I think, is economic, since this is, at root, an
economic problem. It's also one we've talked about here at length on e$.
That solution is postage.

If you use some kind of hash-collision microcoin protocol like
Rivest/Shamir's MicroMint, or the "hash-cash" stuff people have been
talking about on cypherpunks, you end up with a completely off-line,
extremely small value digital cash system which could be used to pay for
stuff like e-mail postage. The only thing you need to do is to encrypt the
payment to the $MTP (:-)) machine, which then sends your mail. The only
overhead is in handling the money, and, since it's handled offline anyway,
the overhead is going to be much less than authenticating signatures either
with an internal table, or, worse, in an on-line scheme of some kind.

However you do the protocol, you probably want to run it on a sender-pays
basis, as that's where all the economic incentive to spam comes from.
Actually, now that I think about it, a truly sender-pays system would mean
that receiver-collects, and so the *receiving* $MTP machine would be the
one which should actually get the money. This is not too far from the idea
of getting paid to read mail, which has also been discussed on cypherpunks
before. The receiving $MTP machine could even raise or lower its postage
price depending on the load at the time, thus auctioning its processing
resources to the highest bidder. People like e-mail spammers, needing to
send messages to you very cheaply would have to wait until the price comes
down. Some of them could wait a very long time. :-).

Frankly, I see no other solution to this problem in the long run except for
postage, which means it's probably time to start figuring out, in earnest,
how to make it all work. Whoever becomes the lowest cost producer of this
kind of software stands to make a whole *bunch* of money.

Cheers,
Bob Hettinga



-----------------
Robert Hettinga (rah@shipwright.com), Philodox
e$, 44 Farquhar Street, Boston, MA 02131 USA
"... however it may deserve respect for its usefulness and antiquity,
[predicting the end of the world] has not been found agreeable to
experience." -- Edward Gibbon, 'Decline and Fall of the Roman Empire'
The e$ Home Page: http://www.shipwright.com/


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-----------------
Robert Hettinga (rah@shipwright.com), Philodox
e$, 44 Farquhar Street, Boston, MA 02131 USA
"... however it may deserve respect for its usefulness and antiquity,
[predicting the end of the world] has not been found agreeable to
experience." -- Edward Gibbon, 'Decline and Fall of the Roman Empire'
The e$ Home Page: http://www.shipwright.com/