From: root@extropia.wimsey.com (Anonymous)
Date: Mon, 31 May 93 22:09:02 PDT
To: cypherpunks@toad.com
Subject: No Subject
Message-ID: <199306010527.AA00963@xtropia>
MIME-Version: 1.0
Content-Type: text/plain


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As shown in Karl Barrus's very useful monthly postings, several people are
running remailers that include encryption.  This gives users the ability to
send messages for which the destination is not visible even to someone
monitoring their outgoing messages.  By chaining through two or more
remailers, no one site can see the mapping between source and destination. 

There is a big potential security weakness with most of these systems that
people should be aware of.  In order to run the decryption program
(currently PGP) automatically, the pass phrase must be provided for the
remailer's secret key.  This means that the pass phrase has to exist, in
the clear, in the scripts which implement the remailer. 

Anyone who has root privileges on the machine which is running the remailer
therefore can get access both to the remailer's secret key file, and to the
pass phrase that unlocks it.  Even momentary acquisition of this power is
enough to capture the secret key. 

Unfortunately, many of the encrypted remailers are running on multi-user
systems over which we have only limited control.  I believe that Miron's
"Extropia" remailer is running on his personal system, so he should be
relatively immune to this attack.  But I think the others are all
vulnerable. 

People should be aware of this when using the remailers.  (This limitation
is one reason I made my remailer keys only 512 bits; I felt there was
little point in going to 1024 bits since the security of the remailer key
can be broken so easily.) 

Until more of us are able to acquire personal Unix boxes it might be wise
to include the Extropia remailer as part of a remailing chain for messages
whose security we care about.  Perhaps Karl could add a notation in his
remailer lists about which machines are public and which are private.  

Hal  

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