TURING's attack against the cycles in the graph also works for non-involutory
rotor machines. Then the graph model is a directed graph and the attacker has
to find directed cycles. These are quite rare, therefore the attack loses most
of its power.
Exercise. Find the directed cycles in the example graphs.
The TURING-WELCHMAN bombe used the involutary characters of the complete Enigma
substitution as well as of the plugboard. The inventors of both of these
»features« apparently didn't see the weaknesses.
Nevertheless the addition of the plugboard made the machine much stronger.
The isomorph attack worked by paper and pencil. Attacking the Wehrmacht Enigma
only worked with the help of heavy machinery.
![[JoGu]](../../JGU.gif)