From: thug@phantom.com (Murdering Thug)
Date: Tue, 26 Jan 93 12:46:59 PST
To: cypherpunks@toad.com
Subject: Re: Computerized OTP (a clarification)
In-Reply-To: <9301261828.AA25565@netcom3.netcom.com>
Message-ID: <m0nGx7v-000jpDC@phantom.com>
MIME-Version: 1.0
Content-Type: text/plain


tcmay@netcom.com writes:

> Sure, one-time pads are information-theoretically secure.
> 
> The problem is the key distribution problem, as well as the storage of
> one-time pads. For example, for the couple of hundred folks on this
> list to communicate securely will other members, each would have to
> meet in person or deliver by trusted courier a one-time pad to _each_
> of the others! A very tough logistical problem, fraught with potential
> weaknesses, and much easier to spoof or break than, for example,
> factoring very large numbers.
> 
> This is the problem, the key distribution problem, that public key
> methods solve.
> 

I never recommended the digital OTP as a replacement for public key
cryptography. Clearly the logistics of using OTPs on a large scale
are clearly dismal.  While public key solutions like PGP are good
for mass communication systems, they are not secure as far as I am
concerned.  I am sure the NSA has plenty of tricks up their sleeve
for dealing with PGP & RSA.

OTP is an excellent solution for small groups (5 people or less) who
MUST have completely secure communications.  It would be quite easy
for a small group like this to physically meet once a year and
exchange their fresh 250mb pads (stored on magnetic reel tape which
is incrementaly shreaded & burned on the way out of a OTP decoding
machine).  In fact only one trusted individual is needed to operate an
OTP pad generating machine to create the fresh pad tapes from RF noise
and only once a year. This could be the ring leader of the group and tape
distributor. 

A 250mb pad is enough for each individual to send 250,000 one kilobyte
messages to his conspirators, surely enough pad material to require physical
pad exchange only once a year, perhaps even less frequently. 

A terrorist group or drug ring could use OTPs quite easily
from a logistical and key distribution point of view and never
have to worry about their messages (e-mail or telex) being
decrypted by any agency on the face of the earth.  The costs of such
a method are minimal for a group of 5 terrorists, a 5-node system like
this could be built and set up for around $5000.

Of course an OTP scheme must insure physical security as well.
Used up key stream tape must be incrementally shredded and burned 
beyond recovery. And plaintext messages should be displayed to CRT,
never be stored. After each message is read or sent, it is destroyed by
being overwritten in RAM by nulls. The screen should either by an LCD
display or a Tempest proof CRT. Unused pad tape must be quickly removable
so that it can be dropped into a near by barrel of sulfuric acid should
the law bust through your door.  This would prevent the capture of the
unused pad tape and prevent the law from spoofing your conspirators by
sending and decoding messages as you. A ventilation system must be
put in place to suck out the fumes from the barrel of acid out of the
room. A wireless alarm system must be in place to allow the detection
of a law enforcement assault and allow the quick acid bath destruction of
unused pad material.  Note, this scheme comes directly from my mind
as I speak and does not fly out of anything.  It could be refined into a
very secure and inexpensive set up.  

A well implemented OTP scheme makes the interception
of plaintext impossible and the capture of messages by physical raids
also impossible.  This is what I believe to be the only provably secure
communication method.  If I was a drug king pin, this is what I would use. 


Thug