Camouflage that message !

[Terry Boon]

On Mon, Sep 24, 2001 at 11:32:04PM +0100, George Foot wrote:

> The first step is to prepare a very large file containing a billion or more
> random bytes.  Identical copies of this file can be made available  to
> anybody interested at little cost -- for example by  distributing the file
> on a CD or a DVD disc.  Call this large file a PAD.
> 
> It is a simple matter to select Pointers to indicate a number, for
> example thirteen, different locations in the Pad and from each of these
> locations to derive a string of random bytes which can then  be
> EORed together to form a new string.  This new string becomes the
> camouflage string for a particular message and is unique to that
> message.

This *may* have similarities to a cipher proposed by Maurer, in

  Ueli M. Maurer, "A Provably-Secure Strongly-Randomized Cipher,"
  Advances in Cryptology -- Eurocrypt '90 Proceedings,
  Springer-Verlag, 1990, pp. 361--373

My conjecture is based on remarks in Bruce Schneier's October 1998
review of the TriStrata system
(http://www.counterpane.com/tristrata.html).  Unfortunately, I don't
have access to Maurer's work to check the relationship between the
ciphers myself.

Section 3.3 of that review suggests that TriStrata uses pointers into
a block of random data to generate a keystream.  Schneier remarks that
a similar technique was first used by Maurer.  Since it also appears
to have similarities to this "Camouflage" proposal, Maurer's work and
any comments on it may be of interest.

-- 
Terry Boon, Hertfordshire, UK
terry@counterfactual.org