[Cryptography] how to detect breakage -- lures etc.??

[Ray Dillinger]

If we're going to bring up rotor machines though, I've got a thought. 
Remember the flat rotors that were made for the bombes?  They had all
their contacts on one side, just because that made it convenient to set
up the machine.  You could pop them in and out independently, without
tearing down a stack and the machine around it, and setting it up
again.  

Why weren't the rotor machines made that way in the first place?
meaning, rotors making contact with contacts on the body of the
machines instead of with each other?

In the first place it allows more flexibility with wiring - outputs
from one wheel could be split between inputs of multiple different
other wheels, or light-board lights illuminated on signals drawn from
more than one wheel, or "extra" outputs of larger rotors beyond the
number needed for the lightboard could be connected back to the "extra"
inputs of the same rotors that take the input from the keyboard on
their other terminals, etc....  As long as each rotor has a definite
input-to-output direction and the wiring respects that parity, it's
guaranteed that all the inputs wind up at the outputs eventually
because there's no place else to go, no way for two signals going the
same input-to-output direction to get connected with each other, and no
way for a signal to get into an infinite loop, because if there's no
way out of a loop then ipso facto there's no way in.  

The kind of wiring you could use with "open face" rotors could be far,
far more difficult to analyze than the "stacked rotor" variety of
machines ever made them. Especially because.... 

In the second place it allows rotors of different sizes, so if you use
six or eight rotors of different sizes with a very large least common
multiple, you don't ever have to NOT MOVE any of them.  They will cycle
into all their permutations, with uniform distributions among those
permutations, just by not having the same period. And you'll have a
very long key stream, and your opponent won't ever get a chance to see
what any proper subset of those rotors do.  And mechanically, it's
brutally simple to just move every rotor one space, every time. That
can easily be made robust, reliable, compact, and lightweight, rather
than intricate, fiddly, and prone to failure. 

So....  why did the stacked-rotor variety ever dominate over the flat-
rotor variety?

				Bear