A proper law

[Ian G Batten]

On Thu, 06 Mar 2003, David Hansen wrote:
> were doing just that. Eventually the Poles told the British (and the 
> French) how to do it

By the way, this is only sort-of true.  The Poles gave Turing et al the
Qwertzu (the wiring of the input rotor), although it's hard to see that
this would have been an obstacle once serious resource was devoted to
the problem, and the capture of any one machine would have revealed it
once and for all as being A->A, B->B, etc.  The bomba and the female
system were critical because they established continuity of break, and
allowed the French and British to understand the structure of the
messages and the message nets for when the going got rough.

However, the Poles' work only broke Enigma up to a point; what they
broke was the indicator system.  They were able to exploit the
properties of the system such that if you _knew_ that the first six
characters were three characters repeated twice, you could massively
reduce the size of the search space you had to attack.  Once the
indicator system changed with the introduction of the Grundstellung and
the indictator group only being sent once, the Poles' work was far less
useful on an ongoing basis.  Yes, the break that had been established up
to that point was critical, and things like the Herrivel tip only worked
because of the knowledge the Poles had given of the machine (knowledge
gained from examination of real Enigmas).  But the Poles' real gift had
been the self-belief that Enigma could be read.  Quite senior people
said ``we don't intend for the Germans to read our stuff, and I doubt
our chaps will read theirs''.

That from the time from the change in the indicator system through to
the Bombes coming on line (note that the Turing/Welchman/et-al bombes
bore little relation to the Polish bomba, and attacked messages rather
than indicators) the break was maintained is probably down to the poles.
After that, it's down to the Bombe and particularly the diagonal board,
and that was Turing, Welchman et al all the way.

ian