From: jerry@terminus.dell.com (Jeremy Porter)
Date: Sat, 22 Jan 94 22:46:28 PST
To: jim@toad.com
Subject: Re: Remailers: The Next Generation
In-Reply-To: <2hq9sv$cdq@uudell.us.dell.com>
Message-ID: <9401230638.AA05002@terminus.us.dell.com>
MIME-Version: 1.0
Content-Type: text/plain


In article <2hq9sv$cdq@uudell.us.dell.com> you write:
>From: jim@bilbo.toad.com (Jim Miller)
>Message-Id: <9401212232.AA06926@bilbo.suite.com>
>Date: Fri, 21 Jan 94 16:32:13 -0600
>To: cypherpunks@toad.com
>Subject: Re: Remailers: The Next Generation
>
>Since the remailer system works better (harder to track messages) as  
>message traffic increases, then perhaps the remailers should circulate  
>bogus messages around the mix in order to sustain a minimum level of  
>traffic.  As more real messages enter the system, the remailers would  
>decrease the number of bogus messages they issue.
>
>How would a remailer tell the difference between a real message and a  
>bogus message from another remailer?  It wouldn't, but that's ok.  All a  
>given remailer cares about is the number of messages coming in versus the  
>number messages that constitute a "good" level of traffic.  If a remailer  
>isn't seeing enough traffic, it would issue some bogus messages that would  
>pass through a random set of remailers and eventually come back to itself.

Hm... actually what one could do is set up a remail/DC-Net combination,
maybe this has already been suggested in a different form, but first
you set up your anon-net, as a virtual ring topology between your remailing
sites.  Alice wants to send an annonymous message to Bob, such that
Bob can reply back without revealing Alice's email address.  First off,
Alice public key encrypts a message to remailer site "Zeta".  This
message contains an encrypted message block to remailer "Iota".  This
message block contains a reply header to remailer "Epsilon".  Zeta receives
a message encypted to it.  It decrypts the messages picks a new remailer,
at some random distance (n/2 + R) hops away.  In this case remailer "Gamma".
Zeta encrypts the message to "Gamma" and inserts it into the
anon-net ring.  When Gamma receives the message, it takes it, decrypts it,
puts the plain message(still encypted by Alice to "Iota") back in.  Iota
gets the message, re-addresses it to yet another remailer chosen at random,
"Delta".  Iota actually builds the final outgoing mail message and that
is what is encrypted to "Delta".  Delta takes the message and mails it
to Bob.  (Alice of course first encrypted the message with Bob's public
key).  Bob can of course reply to the message by prepending the "Epsilon"
message block to his reply, and using encrypting remailing to some remailer,
"Sigma", Bob can reply to Alice's message, protecting Alice's identity
in several different ways.
	Because of the remailer ring using a random number of hops, i.e.
the distance (N/2 + R, where R is between N/2 - 1 and 1), message
latency is random.  Because each message is ecrypted to the upstream
neighbor, direct monitoring is foiled.  By using a fixed size message,
say ~100K, and each site padding any data to the fixed size and including
that in the encrypted data sent to the upstream site, an outside
agency can't monitor packet size to determine anything.  No even
if a spy is in the net, say a remailer at "nsa.gov" any messages passing
through are protected by the difficulty of the encryption.  The site
will know which remailer sites on the ring are being sent to, but
because the the random remailer step in the middle it can't even tell if
the message is incoming or outgoing.  Two sites i.e. "fbi.gov" and nsa.gov,
could work together, but still not getting useful information
most of the time.  Thus, as long as the entrance port to the ring
is not a spy no one knows you are sending anonymous mail.  And assuming
the exit port is not a spy no one knows Bob is receiving aonymous mail.
	Just by putting a few of these ring nodes in places like 
Finland, or even on commerical backbone sites(Alternet, Sprintlink, etc)
makes government monitoring more difficult(or even non government 
monitoring).
	I think this can actually be improved on by hiding the internal
ring identities, but my  brain is not working as well as I would like
and I can't find any detailed info on the "dining sterlight net".
	Actually I think something like this might work well at the
socket level to give a higher bandwidth to directly connected sites,
using mail and mail agents to simulate a token ring network, is not
the most efficient usage of bandwidth, particularly with things like
message length restrictions.
	I've been wanting to set up and play with remailer's but,
my unix host doesn't want to allow |'s in .forward's or the sendmail
aliases.  (I'm assuming this is a feature due to the sendmail bug from
several months ago, I haven't had time to learn sendmail or ask
our resident sendmail expert how to fix it).  


-- 
 Jeremy Porter  -----------------  Systems Enginneering ----
 Dell Computer Corp. --- jerry@terminus.us.dell.com --------
 ------------------------------------------------------------
  Support your Second Amendment rights to encryption technology.