From: Hal <hfinney@shell.portal.com>
Date: Fri, 5 Aug 94 22:11:28 PDT
To: cypherpunks@toad.com
Subject: Re: Remailer ideas
In-Reply-To: <9408051709.AA14763@ah.com>
Message-ID: <199408060511.WAA24892@jobe.shell.portal.com>
MIME-Version: 1.0
Content-Type: text/plain


hughes@ah.com (Eric Hughes) writes:

>Further, in email, there's currently no notion of a connection.  Email
>message are much more like datagrams than bit streams.  In order to do
>reliable delivery, there would have to be persistent state information
>on each side of the communication.  If I send a message for the first
>time to a party and there's no reply, I cannot conclude whether the
>message was not delivered or whether the message was delivered and not
>answered.

>Connection-oriented email would be much more complicated than the
>current systems.  It is, perhaps, time for email to become more
>complex.  

I would really like to see some kind of system for reliable email.  I'm
surprised that it doesn't exist yet.  How many times have we said,
"You didn't get my email?  I'll resend it."  What are computers for, after
all?  Automating repetitive tasks, classically.  This is a perfect appli-
cation.  A copy of outgoing email could be kept, acknowledgements received
on receipt, and the email deleted or re-transmitted as needed.  Serial
numbers would distinguish retransmissions so that redundant resendings
(where the packets "crossed in the mail", so to speak) would be dropped.
All this was designed in an afternoon in Xmodem.  It's conceptually easy.
The hard part is getting a standard and getting people to build it into
their Mail User Agents.

Then, once we had this, we could do another layer for crypto protocols.
Lots of protocols go in stages.  A sends X to B, receives f(X), sends
g(Y,f(X)), etc.  To do this in email would be impossibly cumbersome now,
but the kind of mechanism used for reliable email could be extended to
support these kinds of "stateful" protocols.

As one obvious need for reliable email, consider the transmission of
Chaum-style digital cash.  You don't want to erase your copy until you
are sure the other guy has received it, otherwise your money is permanently
gone (just like when you send cash in postal mail and it is stolen).  But
keeping track of which cash you have sent to which people, who has gotten
theirs, which needs to be re-sent, etc., is painful.  A simple reliable
email method would solve a big part of this problem.

Hal