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1993-07-13 - Re: xor data hiding?

Header Data

From: Douglas Sinclair <dsinclai@acs.ucalgary.ca>
To: mdiehl@triton.unm.edu (J. Michael Diehl)
Message Hash: 96d71b1a3198905021c0af916861e1c40d1baf48f090be51d0cd2246a3276591
Message ID: <9307131439.AA46888@acs1.acs.ucalgary.ca>
Reply To: <9307130230.AA20305@triton.unm.edu>
UTC Datetime: 1993-07-13 14:41:33 UTC
Raw Date: Tue, 13 Jul 93 07:41:33 PDT

Raw message

From: Douglas Sinclair <dsinclai@acs.ucalgary.ca>
Date: Tue, 13 Jul 93 07:41:33 PDT
To: mdiehl@triton.unm.edu (J. Michael Diehl)
Subject: Re: xor data hiding?
In-Reply-To: <9307130230.AA20305@triton.unm.edu>
Message-ID: <9307131439.AA46888@acs1.acs.ucalgary.ca>
MIME-Version: 1.0
Content-Type: text/plain


What you are talking about sounds like the original Vernam cipher that Dave
Kahn talks about in _CodeBreakers_.  There, he was using a teletype with two 
XORing tapes.  One tape was 1000 characters long, the other was 999.  Thus,
999000 characters would have to go past before the system repeated.  HOWEVER,
once it does repeat, all security is compromized.  Even before that time,
I believe there are subtle attacks you can use based on the repetition of the 
keys.  So, this is not a secure cipher method.  I would personally 
suggest tacking an 128 bit IDEA key onto 4dos.com instead.  Or use
DES even.

BTW: Though you could come up with a 30Kb+ string which when XORed would
give you any plaintext, you could not come up with a few small strings
which when used over each other would give you that.  There just isn't enough
information to make that possible.
-- 
PGP 2.3 Key by finger

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