From: wcs@anchor.ho.att.com (bill.stewart@pleasantonca.ncr.com +1-510-484-6204)
Date: Tue, 15 Feb 94 21:29:57 PST
To: boone@psc.edu
Subject: Re:  SCHEME for FULL-SPEC RETURN PATH
Message-ID: <9402160511.AA10151@anchor.ho.att.com>
MIME-Version: 1.0
Content-Type: text/plain


Sorry, either I mixed it up with regular cypherpunks mail or didn't 
realize you were expecting a response.  To summarize your method,
messages going from the original sender to the recipient have headers like

To: recipient
X-Anon-Sender-Path: 
X-Anon-Reply-Path:

where the X-A-*-P: headers have the form
	remaileruser+stuff@remailersite
and "stuff" is similar-sorm stuff encrypted with a remailer's public key.
When going from the sender to the recipient, remailers take their
names off the X-A-S-P line, decrypt the stuff, and encrypt themselves
onto the X-A-R-P line, which the recipient can use to reply.

My two main problems with it are
1) It leaves the recipient's address visible the whole way.
Not only is this a security risk, but the recipient may not have made
it known, since the recipient may have set up some messy remailer-chain
using different syntax to get replies.

2) The syntax may be symmetrical, but it's ugly :-)
It would be cleaner to package it into the To: field if you can, though
the user+stuff@somewhere format seems to be an Andrewism, and the
Internet standard @somewhere.com:user@domain or user%foo@bar.com
forms only carry machine names, not machine and user names.
Because you're not using the standard mailer syntax,
it means that you have to build a chain of only your flavor of remailers
to get a reply to work, though I suppose almost any method has that problem.
But you run the risk of a normal machine or smart-mailer along the way
just seeing the To: recipient@machine.com and sending it directly
instead of sending it to your remailer-user.  Better to keep roughly
your same syntax, except have the To: line be only the next hop,
and the recipient's real address be hidden inside the X-A-S-P pile.
That's also more symmetric, letting you take a reply from this sort
of system and reply back to it again.

		Bill