[4116] in cryptography@c2.net mail archive
Re:
daemon@ATHENA.MIT.EDU (Ben Laurie)
Tue Feb 2 10:43:44 1999
Date: Tue, 02 Feb 1999 10:05:44 +0000
From: Ben Laurie <ben@algroup.co.uk>
To: "Clive D.W. Feather" <clive@davros.org>
Cc: cryptography@c2.net
Clive D.W. Feather wrote:
>
> In article <199901281606.LAA25185@pollen.cs.concordia.ca>, MCKAY john
> <mckay@cs.concordia.ca> writes
> >Another curiosity of the Mark I's instruction set was a sideways
> >add ('population count'), also specified by Turing. I've always
> >assumed that the two instructions could be useful for cryptography -
>
> Think about how the Bombes worked. You injected signal into one line,
> and wanted to know when it didn't come back on all of the other 25. A
> software implementation of this could use a population count to
> advantage.
I don't see how ... this is a known bit pattern, rather than a
particular bit count. A simple XOR and test for zero will do this
efficiently.
Cheers,
Ben.
--
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"My grandfather once told me that there are two kinds of people: those
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