From: "Robert A. Costner" <pooh@efga.org>
Date: Fri, 3 Oct 1997 14:07:24 +0800
To: cypherpunks@cyberpass.net
Subject: Re: Traffic Analysis
In-Reply-To: <199710030423.XAA29605@einstein.ssz.com>
Message-ID: <3.0.3.32.19971003013456.0356271c@mail.atl.bellsouth.net>
MIME-Version: 1.0
Content-Type: text/plain



At 11:23 PM 10/2/97 -0500, Jim Choate wrote:
>Why/how does it decide to throw them away? Does the incoming produce cover
>traffic even if its thrown away? Traffic analysis generaly does not look at
>the contents of the packets, encrypted or not is irrelevant.

Remailers in general will throw away messages at times.  Sometimes on
purpose, sometimes by accident.  This is not replaced by any cover traffic.
 For purposes of argument, we could say that a remailer throws away
messages that violate usage policies.  This accounts for some amount of
traffic, let's just say 10% to name a figure.  Of course this sounds
reprehensible, so you ask what sort of message gets thrown out?  Some
examples might be:

 * 3,000 copies of the same message to the same person
 * Any mail from Sanford Wallace at Cyberpromo.com
 * A 300MB mailbomb

Basically some messages that constitute abuse (without examining actual
content) get tossed.  These are "valid" messages from people which the
remailer might decide to not continue to send.  Much of this mail never
even reaches the remailer code as it gets tossed at an earlier level.
Since about 10% of incoming traffic gets tossed, it would seem that this
would somehow effect traffic analysis.  This traffic is not replaced, and
much of the dropped traffic is not even know to the remailer.  How much
would this actually effect traffic analysis?

As a side point, software problems will at times cause chained messages to
get tossed.  From time to time certain remailers become incompatible with
each other, or user held public keys do not get updated properly.  This
will also cause messages to get tossed.

>By 'nym' you mean each subscribed address or to each address used in the
>outgoing? I would say it is bad to send to subscribers.

Cracker sends messages as "Anonymous" and does not allow replies to be
returned to the sender.  Redneck on the other hand allows each user to pick
a pseudonym and allows relies to be returned to the sender.  This is known
as a "nym".  The whole point of a nym is to be able to receive replies (as
well as establish reputation capital).  People who have nyms on the
remailer want to receive email back to them.  Nyms are managed and
authenticated with PGP.  My question is would it foil traffic analysis if a
number of remailer server generated messages were to go out to the nyms
without ever having matching incoming traffic?

>A commercial remailer should not keep records of its use. However, I suspect
>that eventualy remailers will be required to keep usage records by law.

I'd be willing to be involved in a first amendment challenge against any
such law.  I suspect we would win in the US.  At least we won the last 1st
amendment challenge against remailers.  (ACLU vs Miller)


  -- Robert Costner                  Phone: (770) 512-8746
     Electronic Frontiers Georgia    mailto:pooh@efga.org  
     http://www.efga.org/            run PGP 5.0 for my public key