The symmetric ciphers

Mark H. Wood mwood at IUPUI.Edu
Thu Oct 31 15:00:36 CET 2013

On Wed, Oct 30, 2013 at 11:33:18PM +0100, Philipp Klaus Krause wrote:
> Hash: SHA1
> Is there a known good way to combine multiple symmetric ciphers into
> something that is at least as strong as the weakest of them?

I sincerely doubt that there is, in the general case.  That's the
point: you have to analyze each combination as if it were a new,
untried cipher.  It seems useless to ask whether one can benefit from
composing multiple unspecified symmetric ciphers; much more useful to
ask whether e.g. AES+BLOWFISH is at least as strong as, or stronger
than, either AES or BLOWFISH alone.  Then ask the same question for
each composition you think promising.

You will wind up doing quite a LOT of math.  You could probably get a
book out of it, if you do a thorough job.

Mark H. Wood, Lead System Programmer   mwood at IUPUI.Edu
Machines should not be friendly.  Machines should be obedient.
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