bugtraq - Re: Joint encryption?

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Date: Sun, 20 Feb 2005 13:09:54 +0100 (CET)
From: "Ruud H.G. van Tol" <rvtol@...lution.nl>
To: "John Richard Moser" <nigelenki@...cast.net>
Cc: bugtraq@...urityfocus.com
Subject: Re: Joint encryption?

John wrote:
> The most obvious methods I can think of create explosive data growth
> as M and N increase.  The amount of data needed in any way I can think
> of grows linearly with M and exponentially with N.

The data remains encrypted, until the key is known. So only the key needs to
be distributed. Keywords: Reed-Solomon, FEC, Vandermonde matrices, PAR2.
Extra requirement is, that you don't want 90% of the key known when M=10 and 9
key-secrets are collected, so you need an extra 'layer'.

A change of 1 bit in one 'layer' should change in average 50% of the bits in
the next 'layer', because basically you want each key-bit to remain unknown
(and unguessable) until (at least) M secrets are known.

-- 
Grtz, Ruud