1996-11-26 - Re: IPG Algorith Broken!

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From: paul@fatmans.demon.co.uk
To: Bill Frantz <frantz@netcom.com>
Message Hash: d35155e75553bd0fae22f81093d32ecbfa526db849b2e5b63f6b852004caf279
Message ID: <849030317.93771.0@fatmans.demon.co.uk>
Reply To: N/A
UTC Datetime: 1996-11-26 17:48:41 UTC
Raw Date: Tue, 26 Nov 1996 09:48:41 -0800 (PST)

Raw message

From: paul@fatmans.demon.co.uk
Date: Tue, 26 Nov 1996 09:48:41 -0800 (PST)
To: Bill Frantz <frantz@netcom.com>
Subject: Re: IPG Algorith Broken!
Message-ID: <849030317.93771.0@fatmans.demon.co.uk>
MIME-Version: 1.0
Content-Type: text/plain

 Known-plaintext:   Unbreakable, since the pad is never reused
 Chosen-plaintext:  Unbreakable, ditto
 Adaptive-chosen-plaintext: Unbreakable, ditto

Correct but for a different reason. Re-using the pad does render the 
security useless but the other reason is if we know part of the pad 
AND the ciphertext (and hence the plaintext) or part of the plaintext 
and the ciphertext and therefore the pad, We cannot solve the rest of 
the ciphertext as the pad is true random and the next bits are 
independent of all the previous ones so we cannot predict from what 
we have.

A better definition of unbreakable, IMHO, is that there is no way to 
determine the plaintext given unlimited ciphertext and computational 
resources. Sure, this isn`t a complete definition but at least it 
definites perfect security in an analytic sense.


  Datacomms Technologies web authoring and data security
       Paul Bradley, Paul@fatmans.demon.co.uk
  Paul@crypto.uk.eu.org, Paul@cryptography.uk.eu.org    
      Email for PGP public key, ID: 5BBFAEB1
     "Don`t forget to mount a scratch monkey"