Denys BeauchEmin writes:

>I recommend "Enigma" by Robert Harris.  An excellent novel with a plot
>interwoven with lots of technical details about the goings on at Bletchley
>Park and the process of deciphering Enigma.  Incidentally, you may wish to
>visit http://www.cranfield.ac.uk/ccc/bpark/morebpark.htm
>
>Now some of you may think, what does all this have to do with computers?
> Well, arguably the first computer ever designed and used was the Colossus,
>the first electronic valve computer.  Visit
>http://www.cranfield.ac.uk/ccc/bpark/colossus.htm

It actually has a huge amount to do with computers. Alan Turing's work
was instrumental in creating the machines that cryptanalyzed Enigma, and
much of the work he did on Enigma ultimately became the foundation for
early digital computers. (The best technical biography I've seen of
Turing is no longer in print; it's Andrew Hodges' _Turing: The Enigma_.)

At the other end of the chronological scale, quantum computing is
starting to make surprising progress, both in practical implementations
and in construction of algorithms. It's not at all clear that the
practical problems can be overcome far enough to create usefully large
quantum computers, but if the effort succeeds it will mark a revolution
in computing, starting with cryptography.

All public-key cryptosystems today rely on the difficulty of calculating
discrete logarithms in a finite field -- basically, factoring large
numbers. This problem has been shown to be computationally "hard" in the
technical sense, meaning that the computing time required for a solution
scales exponentially with the size of the problem. (In contrast, a
problem like sorting scales as n^2 in the worst case; this grows much
more slowly than 2^n.) Quantum computers can attack such computationally
"hard" problems very effectively, so a practical quantum computer could
render current public-key cryptosystems ineffective.

-- Bruce


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