From: Anonymous User <nobody@c2.org>someone@someplace.not.far.from.you
Date: Sat, 15 Jun 1996 17:03:55 +0800
To: cypherpunks@toad.com
Subject: Hackerpunks and C2
Message-ID: <199606150405.VAA08966@infinity.c2.org>
MIME-Version: 1.0
Content-Type: text/plain


Ecafe Mixmaster Remailer wrote:
> The proposal for a Hackerpunks nym based mailing list is interesting,
> however, there are some concerns regarding the susceptibility of the list
> to traffic analysis.

I think that the belief of the owner of hackerpunks that s/he won't
be discovered is somewhat naive. Even though your traffic analysis
ideas are right (see below), the most likely way to discover the owner is
his/her unintentional screwup. I just feel like monitoring traffic of 
all internet is too expensive.

Still, the secrecy of the location of the hackerpunks-owner is not such
an important thing (as long as the list is not located in some police
state not honoring free speech). The knowledge of said localtion is 
not even really important since the contents of this list may be
montored anyway by simply subscribing to the list.

> The solution to the two dilemmas seems to be to ask that the C2 re-mailing
> code be modified so as ensure that each messages is padded to a fixed size
> before encrypting and being sent through the reply block. On the other
> hand, this would give away information that anyone receiving messages of
> this fixed length was likely the owner of some C2 nym.

[maybe I saw it on this list] How about this: that every remailer adds
a cookie of size X where

      S == size( message )
      X == 20KB - S + rand( 40KB ) if S < 20KB
      X == 40KB - S + rand( 80KB ) if 20KB <= S < 40KB
      X == 80KB - S + rand( 160KB ) if 40KB <= S < 80KB

and so on. This way, only 2-3 bits of information about size will
be available to traffic analyzers, instead of about 10-12. For the
most typical situation of messages being about 5KB in size, there
is no information leaking.

Of course, if an incoming message contained a cookie, it should be 
dropped by the remailer to be replaced by the new one on the next hop.

Same cookie feature could be added to premail.

Have fun.