Re: Is encrypting twice much more secure?

Peter Fairbrother wrote:

I don't know about screwing up the implementation, which could do
horrible things - but yes, there is established theory that multiple
encryption with statistically independent keys is at least as secure as
the first encryption, see:

M. Maurer and J. L. Massey, Cascade ciphers: The importance of being
first, Journal of Cryptology, vol. 6, no. 1, pp. 55–61, 1993.

www.isiweb.ee.ethz.ch/archive/massey_pub/pdf/BI434.pdf

so if one pass is secure enough you're okay.

(I have a tiny doubt about their result, which I've been working on for
some years now - but in practice it won't mean much even if it pans out)

Wouldn't an 'definition' of 'statistically independent keys' (not very
simple to verify absolutely in practice, I surmise) by itself
('logically') imply that the 2nd cipher couldn't weaken the work of the
1st cipher? (For in the other case one could say then that the keys
aren't 'independent' after all.)

When your work bears fruit, please let us know as soon as possible, for
that would be very interesting and valuable.

M. K. Shen
.

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