From: Carl Ellison <cme@TIS.COM>
Date: Mon, 2 Oct 95 14:09:07 PDT
To: Doug.Hughes@eng.auburn.edu
Subject: Re: worldwide announce: New OTP Mail/FTP apps
In-Reply-To: <199510020556.WAA01007@comsec.com>
Message-ID: <9510022103.AA10569@tis.com>
MIME-Version: 1.0
Content-Type: text/plain


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>From: Doug Hughes <Doug.Hughes@eng.auburn.edu>
>Date: Thu, 28 Sep 1995 19:31:00 -0500



>A company in Israel named Elementrix has just announce at Interop an
>entirely new paradigm in secure transactions. They have a secure
>one time pad that allows people to exchange mail and ftp files back
>in forth in complete security without the worries of key management
>or storage or secure random number generation or synchronization.


As far as I could tell from your description, this is an autokey cipher --
not a OTP.  

An autokey cipher starts with a shared secret key and uses previous
plaintext or ciphertext as part of the key.  DES CBC is an autokey cipher.

The original autokey used previous plaintext or ciphertext as the only key.
More modern ones mix in the previous text.

I had a design for one, several years ago, which kept a mapping in memory
and changed the mapping based on incoming plaintext.  Therefore, there is
state information kept at both sides which keeps changing.

One might think that if the attacker never gets in, today's randomness is
just as good as yesterday's.  That might even be true.  However, there are
many openings for finding relationships between yesterday's and today's
ciphertexts.

I look forward to seeing the actual algorithm.

 - Carl

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