From: VACCINIA@UNCVX1.OIT.UNC.EDU
Date: Sat, 27 Nov 93 14:49:44 PST
To: cypherpunks@toad.com
Subject: Traffic analysis and file size
Message-ID: <01H5THL70MTE000B3T@UNCVX1.OIT.UNC.EDU>
MIME-Version: 1.0
Content-Type: text/plain


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There has been some list discussion about defeating traffic analysis of 
remailers by altering the incoming and outgoing size of the files. But 
is this not accomplished by merely encrypting with the remailers public key?
Assuming it is an encryption supporting remailer that is. When the file size 
changes as PGP encryption is stripped off it and the files are not sent out 
in the exact same order as they arrive, would it not be very difficult to 
ascertain that file of size X enters a remailer and emerges as size X-y. Or
can one easily deduce y from PGP's parameters? Even if y is easily deduced 
this problem can be overcome.

I have used various layers of compression utilities and encryption to change 
message size so that as the first layer of encryption is stripped off, the 
file is then in a File.zip state. This is then unzipped revealing another
encrypted message with an address header. Upon being sent to the next series 
of remailers this same course of events could then be replicated ad nauseum. 
Combine this strategy with file stuffers and one would likely have a hell of 
a time trying to match incoming/outgoing file sizes and where they originated 
from/are going to. Granted this is a pain, but it would seem that automation 
could easily be implemented.

Scott G. Morham             !The First, 
Vaccinia@uncvx1.oit.unc.edu !           Second
PGP Public Keys by Request  !                  and Third Levels
                            !        of Information Storage and Retrieval
                            !DNA,                       
                            !     Biological Neural Nets,
                            !                             Cyberspace

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