[GreenKeys] The Cipher Event at Bletchley Park

[Craig Sawyers]

> The Cipher Event.

Um - guilty as charged.  I restored that Lorenz SZ42 to full functionality
around 5 years ago.  Actually *the* SZ42, since it looks like the only
complete one on the planet.  There is a display exhibit at the National
Crytologic Museum in Maryland, and two part units somewhere in Norway.  But
the Bletchley SZ42 is complete with all bells and whistles, and is now
completely functional.

I'm accompanying it out to Germany, setting it up, and dealing with the
media (and there is a lot of media interest; the SZ42 was used only for
communication from the field commanders to Hitler's Berlin bunker.

Breaking the messages before Colossus produces a result will be an
interesting challenge.  The SZ42 has 10^19 possible initial settings, and a
further randomisation in that the ciphertext is modified by two's
complementing with one of the clear text bits (a so called "limitation" in
WW2 Bletchley-speak).  When Colossus was used originally, it was expected to
produce a first try in around 15 minutes.  This told what the machine
settings were, and these could be set onto a mechanical analogue of the SZ42
to enable the cipher text to be converted to clear text.  Bletchely worked
out what the function of the SZ42 was, and built the analogue machine,
without seeing an SZ42 - the first one that they saw was the one I restored,
after it was captured in 1945.

Should be absolutely fascinating.  Hope the damned thing works OK!  They
were not known for their reliability - communications convoys had two, and
when one played up they could switch in the second one!!

Craig