[GreenKeys] Enigma machines

[Craig Sawyers]

>     The reason it only has three rotors is that if they added
> more, the
> key forces required would be hopelessly high.  There was a 4-rotor
> Enigma variant, but that never caught on.  Machines with more
> rotors were built, but they were motor-driven, not manual, and
> the WWII-vintage ones were bigger than a Teletype model 15.

No, not really.  Three rotors was felt to be secure enough for the first few
years of the War, and required the combined ingenuity of the Polish and then
the British at Bletchley Park to regularly break the codes.  The so-called
Bombe was basically racks of motor driven three-wheel enigmas running in
parallel. Patch wiring and initial setting was made according to a "crib"
that was worked out by hand by cryptographers.

The four-wheel enigma was introduced by the Germans in early 1942 to
increase coding security.  This gave Bletchley a major problem, giving a
break black-out of several months.  The Bombe was hastily redesigned to add
a fourth high-speed rotor (to give the same speed of break as the
three-wheel, the fourth rotor had to go 26 times the speed of the third).
The breakthrough came when U559 was forced to the surface after prolonged
depth charging - four British seamen went aboard and managed to recover two
crucial code books before the U-boat sunk and drowned two of the seamen.
That gave much more information to Bletchey who, with the modified Bombe
succeeded in regularly breaking the 4-wheel.

Whether or not it was hard to use is beside the point - it became a standard
Enigma Machine variant in wide use in the later years of the war.

For a good grounding on all this stuff, have a look at Tony Sale's website
http://www.codesandciphers.org.uk/ .  Tony was responsible for the rebuild
of Colossus.  Post WW2 Tony was an MI5 operative, through the height of the
cold war; he has some fascinating reminiscences!

Craig