From: cjl <cjl@welchlink.welch.jhu.edu>
Date: Wed, 3 Aug 94 13:28:16 PDT
To: Cypherpunks mailing list <cypherpunks@toad.com>
Subject: Remailer traffic analysis foiling
Message-ID: <Pine.3.89.9408031548.A5899-0100000@welchlink.welch.jhu.edu>
MIME-Version: 1.0
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Remailer hackers,

I've been thinking about the problem of traffic analysis of anonymous 
remailers and I have a question to pose to those of you whose thoughts on 
this topic are "more frequent or fully-formed".  

Would there be any advantage to giving remailers a MIRV capability?  

The idea goes like this:

The message arrives, the PGP wrapper is removed, the message is scanned 
for some specific token imbedded in the text (ala Matt Ghio's Cutmarks 
function).  That token is a divider between two outbound messages.  
These messages are sent along their respective ways.  The result is 
something like a 10K message coming in, and a 7K and a 3K message leaving.
If one of these goes to the bit bucket, it is like having added padding 
stripped off.  Alternately they each could be part of the real message, 
previously split and then sent via different paths to reduce chances of 
complete message interception.

I guess the issues involved are:

1)  How difficult would this be to code?  [Yeah, yeah "Cypherpunks write 
    code"(TM), but some of us write genetic code, not computer code :-)]

2)  What is the credible threat of traffic analysis?
	a)  Does multiplication of messages and their routing schemes create 
            problems of scale for these alleged eavesdropers?
        b)  Do you assume that if it's not a compromised server, that 
	    what goes on inside the machine is hidden? 

Now before the Zippos start flicking, I've followed the the latency vs. 
reordering argument, and accept that latency *may* acheive reordering, but 
not necessarily.  In this system though, different latencies after the 
split would seem to acheive something because without reliable size in/out 
information it would be harder to correlate message in with messages out.

Comments (incendiary or or otherwise) requested.
 
C. J. Leonard                     (    /      "DNA is groovy"
                                   \ /                - Watson & Crick
<cjl@welchlink.welch.jhu.edu>      / \     <--  major groove
                                  (    \
Finger for public key               \   )
Strong-arm for secret key             /    <--  minor groove
Thumb-screws for pass-phrase        /   )